[flang][OpenMP] Upstream do concurrent loop-nest detection.
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This PR starts the effort to upstream AMD's internal implementation of `do concurrent` to OpenMP mapping. This replaces llvm#77285 since we extended this WIP quite a bit on our fork over the past year. An important part of this PR is a document that describes the current status downstream, the upstreaming status, and next steps to make this pass much more useful. In addition to this document, this PR also contains the skeleton of the pass (no useful transformations are done yet) and some testing for the added command line options.
Upstreams the next part of `do concurrent` to OpenMP mapping pass (from AMD's ROCm implementation). See llvm#126026 for more context. This PR add loop nest detection logic. This enables us to discover muli-range `do concurrent` loops and then map them as "collapsed" loop nests to OpenMP.
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@llvm/pr-subscribers-clang-driver @llvm/pr-subscribers-flang-driver Author: Kareem Ergawy (ergawy) ChangesUpstreams the next part of This PR add loop nest detection logic. This enables us to discover This is a follow up for #126026, only the latest commit is relevant. Patch is 39.64 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/127478.diff 19 Files Affected:
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 5ad187926e710..0cd3dfd3fb29d 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -6927,6 +6927,10 @@ defm loop_versioning : BoolOptionWithoutMarshalling<"f", "version-loops-for-stri
def fhermetic_module_files : Flag<["-"], "fhermetic-module-files">, Group<f_Group>,
HelpText<"Emit hermetic module files (no nested USE association)">;
+
+def fdo_concurrent_to_openmp_EQ : Joined<["-"], "fdo-concurrent-to-openmp=">,
+ HelpText<"Try to map `do concurrent` loops to OpenMP [none|host|device]">,
+ Values<"none, host, device">;
} // let Visibility = [FC1Option, FlangOption]
def J : JoinedOrSeparate<["-"], "J">,
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index 9ad795edd724d..cb0b00a2fd699 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -153,7 +153,8 @@ void Flang::addCodegenOptions(const ArgList &Args,
CmdArgs.push_back("-fversion-loops-for-stride");
Args.addAllArgs(CmdArgs,
- {options::OPT_flang_experimental_hlfir,
+ {options::OPT_fdo_concurrent_to_openmp_EQ,
+ options::OPT_flang_experimental_hlfir,
options::OPT_flang_deprecated_no_hlfir,
options::OPT_fno_ppc_native_vec_elem_order,
options::OPT_fppc_native_vec_elem_order,
diff --git a/flang/docs/DoConcurrentConversionToOpenMP.md b/flang/docs/DoConcurrentConversionToOpenMP.md
new file mode 100644
index 0000000000000..de2525dd8b57d
--- /dev/null
+++ b/flang/docs/DoConcurrentConversionToOpenMP.md
@@ -0,0 +1,229 @@
+<!--===- docs/DoConcurrentMappingToOpenMP.md
+
+ Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ See https://llvm.org/LICENSE.txt for license information.
+ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+-->
+
+# `DO CONCURRENT` mapping to OpenMP
+
+```{contents}
+---
+local:
+---
+```
+
+This document seeks to describe the effort to parallelize `do concurrent` loops
+by mapping them to OpenMP worksharing constructs. The goals of this document
+are:
+* Describing how to instruct `flang` to map `DO CONCURRENT` loops to OpenMP
+ constructs.
+* Tracking the current status of such mapping.
+* Describing the limitations of the current implementation.
+* Describing next steps.
+* Tracking the current upstreaming status (from the AMD ROCm fork).
+
+## Usage
+
+In order to enable `do concurrent` to OpenMP mapping, `flang` adds a new
+compiler flag: `-fdo-concurrent-to-openmp`. This flag has 3 possible values:
+1. `host`: this maps `do concurrent` loops to run in parallel on the host CPU.
+ This maps such loops to the equivalent of `omp parallel do`.
+2. `device`: this maps `do concurrent` loops to run in parallel on a target device.
+ This maps such loops to the equivalent of
+ `omp target teams distribute parallel do`.
+3. `none`: this disables `do concurrent` mapping altogether. In that case, such
+ loops are emitted as sequential loops.
+
+The `-fdo-concurrent-to-openmp` compiler switch is currently available only when
+OpenMP is also enabled. So you need to provide the following options to flang in
+order to enable it:
+```
+flang ... -fopenmp -fdo-concurrent-to-openmp=[host|device|none] ...
+```
+For mapping to device, the target device architecture must be specified as well.
+See `-fopenmp-targets` and `--offload-arch` for more info.
+
+## Current status
+
+Under the hood, `do concurrent` mapping is implemented in the
+`DoConcurrentConversionPass`. This is still an experimental pass which means
+that:
+* It has been tested in a very limited way so far.
+* It has been tested mostly on simple synthetic inputs.
+
+### Loop nest detection
+
+On the `FIR` dialect level, the following loop:
+```fortran
+ do concurrent(i=1:n, j=1:m, k=1:o)
+ a(i,j,k) = i + j + k
+ end do
+```
+is modelled as a nest of `fir.do_loop` ops such that an outer loop's region
+contains **only** the following:
+ 1. The operations needed to assign/update the outer loop's induction variable.
+ 1. The inner loop itself.
+
+So the MLIR structure for the above example looks similar to the following:
+```
+ fir.do_loop %i_idx = %34 to %36 step %c1 unordered {
+ %i_idx_2 = fir.convert %i_idx : (index) -> i32
+ fir.store %i_idx_2 to %i_iv#1 : !fir.ref<i32>
+
+ fir.do_loop %j_idx = %37 to %39 step %c1_3 unordered {
+ %j_idx_2 = fir.convert %j_idx : (index) -> i32
+ fir.store %j_idx_2 to %j_iv#1 : !fir.ref<i32>
+
+ fir.do_loop %k_idx = %40 to %42 step %c1_5 unordered {
+ %k_idx_2 = fir.convert %k_idx : (index) -> i32
+ fir.store %k_idx_2 to %k_iv#1 : !fir.ref<i32>
+
+ ... loop nest body goes here ...
+ }
+ }
+ }
+```
+This applies to multi-range loops in general; they are represented in the IR as
+a nest of `fir.do_loop` ops with the above nesting structure.
+
+Therefore, the pass detects such "perfectly" nested loop ops to identify multi-range
+loops and map them as "collapsed" loops in OpenMP.
+
+#### Further info regarding loop nest detection
+
+Loop nest detection is currently limited to the scenario described in the previous
+section. However, this is quite limited and can be extended in the future to cover
+more cases. For example, for the following loop nest, even though, both loops are
+perfectly nested; at the moment, only the outer loop is parallelized:
+```fortran
+do concurrent(i=1:n)
+ do concurrent(j=1:m)
+ a(i,j) = i * j
+ end do
+end do
+```
+
+Similarly, for the following loop nest, even though the intervening statement `x = 41`
+does not have any memory effects that would affect parallelization, this nest is
+not parallelized as well (only the outer loop is).
+
+```fortran
+do concurrent(i=1:n)
+ x = 41
+ do concurrent(j=1:m)
+ a(i,j) = i * j
+ end do
+end do
+```
+
+The above also has the consequence that the `j` variable will **not** be
+privatized in the OpenMP parallel/target region. In other words, it will be
+treated as if it was a `shared` variable. For more details about privatization,
+see the "Data environment" section below.
+
+See `flang/test/Transforms/DoConcurrent/loop_nest_test.f90` for more examples
+of what is and is not detected as a perfect loop nest.
+
+<!--
+More details about current status will be added along with relevant parts of the
+implementation in later upstreaming patches.
+-->
+
+## Next steps
+
+This section describes some of the open questions/issues that are not tackled yet
+even in the downstream implementation.
+
+### Delayed privatization
+
+So far, we emit the privatization logic for IVs inline in the parallel/target
+region. This is enough for our purposes right now since we don't
+localize/privatize any sophisticated types of variables yet. Once we have need
+for more advanced localization through `do concurrent`'s locality specifiers
+(see below), delayed privatization will enable us to have a much cleaner IR.
+Once delayed privatization's implementation upstream is supported for the
+required constructs by the pass, we will move to it rather than inlined/early
+privatization.
+
+### Locality specifiers for `do concurrent`
+
+Locality specifiers will enable the user to control the data environment of the
+loop nest in a more fine-grained way. Implementing these specifiers on the
+`FIR` dialect level is needed in order to support this in the
+`DoConcurrentConversionPass`.
+
+Such specifiers will also unlock a potential solution to the
+non-perfectly-nested loops' IVs issue described above. In particular, for a
+non-perfectly nested loop, one middle-ground proposal/solution would be to:
+* Emit the loop's IV as shared/mapped just like we do currently.
+* Emit a warning that the IV of the loop is emitted as shared/mapped.
+* Given support for `LOCAL`, we can recommend the user to explicitly
+ localize/privatize the loop's IV if they choose to.
+
+#### Sharing TableGen clause records from the OpenMP dialect
+
+At the moment, the FIR dialect does not have a way to model locality specifiers
+on the IR level. Instead, something similar to early/eager privatization in OpenMP
+is done for the locality specifiers in `fir.do_loop` ops. Having locality specifier
+modelled in a way similar to delayed privatization (i.e. the `omp.private` op) and
+reductions (i.e. the `omp.declare_reduction` op) can make mapping `do concurrent`
+to OpenMP (and other parallel programming models) much easier.
+
+Therefore, one way to approach this problem is to extract the TableGen records
+for relevant OpenMP clauses in a shared dialect for "data environment management"
+and use these shared records for OpenMP, `do concurrent`, and possibly OpenACC
+as well.
+
+#### Supporting reductions
+
+Similar to locality specifiers, mapping reductions from `do concurrent` to OpenMP
+is also still an open TODO. We can potentially extend the MLIR infrastructure
+proposed in the previous section to share reduction records among the different
+relevant dialects as well.
+
+### More advanced detection of loop nests
+
+As pointed out earlier, any intervening code between the headers of 2 nested
+`do concurrent` loops prevents us from detecting this as a loop nest. In some
+cases this is overly conservative. Therefore, a more flexible detection logic
+of loop nests needs to be implemented.
+
+### Data-dependence analysis
+
+Right now, we map loop nests without analysing whether such mapping is safe to
+do or not. We probably need to at least warn the user of unsafe loop nests due
+to loop-carried dependencies.
+
+### Non-rectangular loop nests
+
+So far, we did not need to use the pass for non-rectangular loop nests. For
+example:
+```fortran
+do concurrent(i=1:n)
+ do concurrent(j=i:n)
+ ...
+ end do
+end do
+```
+We defer this to the (hopefully) near future when we get the conversion in a
+good share for the samples/projects at hand.
+
+### Generalizing the pass to other parallel programming models
+
+Once we have a stable and capable `do concurrent` to OpenMP mapping, we can take
+this in a more generalized direction and allow the pass to target other models;
+e.g. OpenACC. This goal should be kept in mind from the get-go even while only
+targeting OpenMP.
+
+
+## Upstreaming status
+
+- [x] Command line options for `flang` and `bbc`.
+- [x] Conversion pass skeleton (no transormations happen yet).
+- [x] Status description and tracking document (this document).
+- [x] Loop nest detection to identify multi-range loops.
+- [ ] Basic host/CPU mapping support.
+- [ ] Basic device/GPU mapping support.
+- [ ] More advanced host and device support (expaned to multiple items as needed).
diff --git a/flang/docs/index.md b/flang/docs/index.md
index c35f634746e68..913e53d4cfed9 100644
--- a/flang/docs/index.md
+++ b/flang/docs/index.md
@@ -50,6 +50,7 @@ on how to get in touch with us and to learn more about the current status.
DebugGeneration
Directives
DoConcurrent
+ DoConcurrentConversionToOpenMP
Extensions
F202X
FIRArrayOperations
diff --git a/flang/include/flang/Frontend/CodeGenOptions.def b/flang/include/flang/Frontend/CodeGenOptions.def
index deb8d1aede518..13cda965600b5 100644
--- a/flang/include/flang/Frontend/CodeGenOptions.def
+++ b/flang/include/flang/Frontend/CodeGenOptions.def
@@ -41,5 +41,7 @@ ENUM_CODEGENOPT(DebugInfo, llvm::codegenoptions::DebugInfoKind, 4, llvm::codeg
ENUM_CODEGENOPT(VecLib, llvm::driver::VectorLibrary, 3, llvm::driver::VectorLibrary::NoLibrary) ///< Vector functions library to use
ENUM_CODEGENOPT(FramePointer, llvm::FramePointerKind, 2, llvm::FramePointerKind::None) ///< Enable the usage of frame pointers
+ENUM_CODEGENOPT(DoConcurrentMapping, DoConcurrentMappingKind, 2, DoConcurrentMappingKind::DCMK_None) ///< Map `do concurrent` to OpenMP
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
diff --git a/flang/include/flang/Frontend/CodeGenOptions.h b/flang/include/flang/Frontend/CodeGenOptions.h
index f19943335737b..23d99e1f0897a 100644
--- a/flang/include/flang/Frontend/CodeGenOptions.h
+++ b/flang/include/flang/Frontend/CodeGenOptions.h
@@ -15,6 +15,7 @@
#ifndef FORTRAN_FRONTEND_CODEGENOPTIONS_H
#define FORTRAN_FRONTEND_CODEGENOPTIONS_H
+#include "flang/Optimizer/OpenMP/Utils.h"
#include "llvm/Frontend/Debug/Options.h"
#include "llvm/Frontend/Driver/CodeGenOptions.h"
#include "llvm/Support/CodeGen.h"
@@ -143,6 +144,10 @@ class CodeGenOptions : public CodeGenOptionsBase {
/// (-mlarge-data-threshold).
uint64_t LargeDataThreshold;
+ /// Optionally map `do concurrent` loops to OpenMP. This is only valid of
+ /// OpenMP is enabled.
+ using DoConcurrentMappingKind = flangomp::DoConcurrentMappingKind;
+
// Define accessors/mutators for code generation options of enumeration type.
#define CODEGENOPT(Name, Bits, Default)
#define ENUM_CODEGENOPT(Name, Type, Bits, Default) \
diff --git a/flang/include/flang/Optimizer/OpenMP/Passes.h b/flang/include/flang/Optimizer/OpenMP/Passes.h
index feb395f1a12db..c67bddbcd2704 100644
--- a/flang/include/flang/Optimizer/OpenMP/Passes.h
+++ b/flang/include/flang/Optimizer/OpenMP/Passes.h
@@ -13,6 +13,7 @@
#ifndef FORTRAN_OPTIMIZER_OPENMP_PASSES_H
#define FORTRAN_OPTIMIZER_OPENMP_PASSES_H
+#include "flang/Optimizer/OpenMP/Utils.h"
#include "mlir/Dialect/Func/IR/FuncOps.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/Pass/Pass.h"
@@ -30,6 +31,7 @@ namespace flangomp {
/// divided into units of work.
bool shouldUseWorkshareLowering(mlir::Operation *op);
+std::unique_ptr<mlir::Pass> createDoConcurrentConversionPass(bool mapToDevice);
} // namespace flangomp
#endif // FORTRAN_OPTIMIZER_OPENMP_PASSES_H
diff --git a/flang/include/flang/Optimizer/OpenMP/Passes.td b/flang/include/flang/Optimizer/OpenMP/Passes.td
index 3add0c560f88d..fcc7a4ca31fef 100644
--- a/flang/include/flang/Optimizer/OpenMP/Passes.td
+++ b/flang/include/flang/Optimizer/OpenMP/Passes.td
@@ -50,6 +50,36 @@ def FunctionFilteringPass : Pass<"omp-function-filtering"> {
];
}
+def DoConcurrentConversionPass : Pass<"omp-do-concurrent-conversion", "mlir::func::FuncOp"> {
+ let summary = "Map `DO CONCURRENT` loops to OpenMP worksharing loops.";
+
+ let description = [{ This is an experimental pass to map `DO CONCURRENT` loops
+ to their correspnding equivalent OpenMP worksharing constructs.
+
+ For now the following is supported:
+ - Mapping simple loops to `parallel do`.
+
+ Still TODO:
+ - More extensive testing.
+ }];
+
+ let dependentDialects = ["mlir::omp::OpenMPDialect"];
+
+ let options = [
+ Option<"mapTo", "map-to",
+ "flangomp::DoConcurrentMappingKind",
+ /*default=*/"flangomp::DoConcurrentMappingKind::DCMK_None",
+ "Try to map `do concurrent` loops to OpenMP [none|host|device]",
+ [{::llvm::cl::values(
+ clEnumValN(flangomp::DoConcurrentMappingKind::DCMK_None,
+ "none", "Do not lower `do concurrent` to OpenMP"),
+ clEnumValN(flangomp::DoConcurrentMappingKind::DCMK_Host,
+ "host", "Lower to run in parallel on the CPU"),
+ clEnumValN(flangomp::DoConcurrentMappingKind::DCMK_Device,
+ "device", "Lower to run in parallel on the GPU")
+ )}]>,
+ ];
+}
// Needs to be scheduled on Module as we create functions in it
def LowerWorkshare : Pass<"lower-workshare", "::mlir::ModuleOp"> {
diff --git a/flang/include/flang/Optimizer/OpenMP/Utils.h b/flang/include/flang/Optimizer/OpenMP/Utils.h
new file mode 100644
index 0000000000000..636c768b016b7
--- /dev/null
+++ b/flang/include/flang/Optimizer/OpenMP/Utils.h
@@ -0,0 +1,26 @@
+//===-- Optimizer/OpenMP/Utils.h --------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_OPTIMIZER_OPENMP_UTILS_H
+#define FORTRAN_OPTIMIZER_OPENMP_UTILS_H
+
+namespace flangomp {
+
+enum class DoConcurrentMappingKind {
+ DCMK_None, ///< Do not lower `do concurrent` to OpenMP.
+ DCMK_Host, ///< Lower to run in parallel on the CPU.
+ DCMK_Device ///< Lower to run in parallel on the GPU.
+};
+
+} // namespace flangomp
+
+#endif // FORTRAN_OPTIMIZER_OPENMP_UTILS_H
diff --git a/flang/include/flang/Optimizer/Passes/Pipelines.h b/flang/include/flang/Optimizer/Passes/Pipelines.h
index ef5d44ded706c..a3f59ee8dd013 100644
--- a/flang/include/flang/Optimizer/Passes/Pipelines.h
+++ b/flang/include/flang/Optimizer/Passes/Pipelines.h
@@ -128,6 +128,17 @@ void createHLFIRToFIRPassPipeline(
mlir::PassManager &pm, bool enableOpenMP,
llvm::OptimizationLevel optLevel = defaultOptLevel);
+struct OpenMPFIRPassPipelineOpts {
+ /// Whether code is being generated for a target device rather than the host
+ /// device
+ bool isTargetDevice;
+
+ /// Controls how to map `do concurrent` loops; to device, host, or none at
+ /// all.
+ Fortran::frontend::CodeGenOptions::DoConcurrentMappingKind
+ doConcurrentMappingKind;
+};
+
/// Create a pass pipeline for handling certain OpenMP transformations needed
/// prior to FIR lowering.
///
@@ -135,9 +146,10 @@ void createHLFIRToFIRPassPipeline(
/// that the FIR is correct with respect to OpenMP operations/attributes.
///
/// \param pm - MLIR pass manager that will hold the pipeline definition.
-/// \param isTargetDevice - Whether code is being generated for a target device
-/// rather than the host device.
-void createOpenMPFIRPassPipeline(mlir::PassManager &pm, bool isTargetDevice);
+/// \param opts - options to control OpenMP code-gen; see struct docs for more
+/// details.
+void createOpenMPFIRPassPipeline(mlir::PassManager &pm,
+ OpenMPFIRPassPipelineOpts opts);
#if !defined(FLANG_EXCLUDE_CODEGEN)
void createDebugPasses(mlir::PassManager &pm,
diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index f3d9432c62d3b..809e423f5aae9 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -157,6 +157,32 @@ static bool parseDebugArgs(Fortran::frontend::CodeGenOptions &opts,
return true;
}
+static void parseDoConcurrentMapping(Fortran::frontend::CodeGenOptions &opts,
+ llvm::opt::ArgList &args,
+ clang::DiagnosticsEngine &diags) {
+ llvm::opt::Arg *arg =
+ args.getLastArg(clang::driver::options::OPT_fdo_concurrent_to_openmp_EQ);
+ if (!arg)
+ return;
+
+ using DoConcurrentMappingKind =
+ Fortran::frontend::CodeGenOptions::DoConcurrentMappingKind;
+ std::optional<DoConcurrentMappingKind> val =
+ llvm::StringSwitch<std::optional<DoConcurrentMappingKind>>(
+ arg->getValue())
+ .Case("none", DoConcurrentMappingKind::DCMK_None)
+ .Case("host", DoConcurrentMappingKind::DCMK_Host)
+ .Case("device", DoConcurrentMappingKind::DCMK_Device)
+ .Default(std::nullopt);
+
+ if (!val.has_value()) {
+ diags.Report(clang::diag::err_drv_invalid_value)
+ << arg->getAsString(args) << arg->getValue();
+ }
+
+ opts.setDoConcurrentMapping(val.value());
+}
+
static bool parseVectorLibArg(Fortran::frontend::CodeGenOptions &opts,
llvm::opt::ArgList &args,
clang::DiagnosticsEngine &diags) {
@@ -426,6 +452,8 @@ static void parseCodeGenArgs(Fortran::frontend::CodeGenOptions &opts,
clang::driver::options::OPT_funderscoring, false)) {
opts.Underscoring = 0;
}
+
+ parseDoConcurrentMapping(opts, args, diags);
}
/// Parses all target input arguments and populates the target
diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
index 763c810ace0eb..ccc8c7d96135f 100644
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cp...
[truncated]
|
|
@llvm/pr-subscribers-flang-fir-hlfir Author: Kareem Ergawy (ergawy) ChangesUpstreams the next part of This PR add loop nest detection logic. This enables us to discover This is a follow up for #126026, only the latest commit is relevant. Patch is 39.64 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/127478.diff 19 Files Affected:
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 5ad187926e710..0cd3dfd3fb29d 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -6927,6 +6927,10 @@ defm loop_versioning : BoolOptionWithoutMarshalling<"f", "version-loops-for-stri
def fhermetic_module_files : Flag<["-"], "fhermetic-module-files">, Group<f_Group>,
HelpText<"Emit hermetic module files (no nested USE association)">;
+
+def fdo_concurrent_to_openmp_EQ : Joined<["-"], "fdo-concurrent-to-openmp=">,
+ HelpText<"Try to map `do concurrent` loops to OpenMP [none|host|device]">,
+ Values<"none, host, device">;
} // let Visibility = [FC1Option, FlangOption]
def J : JoinedOrSeparate<["-"], "J">,
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index 9ad795edd724d..cb0b00a2fd699 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -153,7 +153,8 @@ void Flang::addCodegenOptions(const ArgList &Args,
CmdArgs.push_back("-fversion-loops-for-stride");
Args.addAllArgs(CmdArgs,
- {options::OPT_flang_experimental_hlfir,
+ {options::OPT_fdo_concurrent_to_openmp_EQ,
+ options::OPT_flang_experimental_hlfir,
options::OPT_flang_deprecated_no_hlfir,
options::OPT_fno_ppc_native_vec_elem_order,
options::OPT_fppc_native_vec_elem_order,
diff --git a/flang/docs/DoConcurrentConversionToOpenMP.md b/flang/docs/DoConcurrentConversionToOpenMP.md
new file mode 100644
index 0000000000000..de2525dd8b57d
--- /dev/null
+++ b/flang/docs/DoConcurrentConversionToOpenMP.md
@@ -0,0 +1,229 @@
+<!--===- docs/DoConcurrentMappingToOpenMP.md
+
+ Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ See https://llvm.org/LICENSE.txt for license information.
+ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+-->
+
+# `DO CONCURRENT` mapping to OpenMP
+
+```{contents}
+---
+local:
+---
+```
+
+This document seeks to describe the effort to parallelize `do concurrent` loops
+by mapping them to OpenMP worksharing constructs. The goals of this document
+are:
+* Describing how to instruct `flang` to map `DO CONCURRENT` loops to OpenMP
+ constructs.
+* Tracking the current status of such mapping.
+* Describing the limitations of the current implementation.
+* Describing next steps.
+* Tracking the current upstreaming status (from the AMD ROCm fork).
+
+## Usage
+
+In order to enable `do concurrent` to OpenMP mapping, `flang` adds a new
+compiler flag: `-fdo-concurrent-to-openmp`. This flag has 3 possible values:
+1. `host`: this maps `do concurrent` loops to run in parallel on the host CPU.
+ This maps such loops to the equivalent of `omp parallel do`.
+2. `device`: this maps `do concurrent` loops to run in parallel on a target device.
+ This maps such loops to the equivalent of
+ `omp target teams distribute parallel do`.
+3. `none`: this disables `do concurrent` mapping altogether. In that case, such
+ loops are emitted as sequential loops.
+
+The `-fdo-concurrent-to-openmp` compiler switch is currently available only when
+OpenMP is also enabled. So you need to provide the following options to flang in
+order to enable it:
+```
+flang ... -fopenmp -fdo-concurrent-to-openmp=[host|device|none] ...
+```
+For mapping to device, the target device architecture must be specified as well.
+See `-fopenmp-targets` and `--offload-arch` for more info.
+
+## Current status
+
+Under the hood, `do concurrent` mapping is implemented in the
+`DoConcurrentConversionPass`. This is still an experimental pass which means
+that:
+* It has been tested in a very limited way so far.
+* It has been tested mostly on simple synthetic inputs.
+
+### Loop nest detection
+
+On the `FIR` dialect level, the following loop:
+```fortran
+ do concurrent(i=1:n, j=1:m, k=1:o)
+ a(i,j,k) = i + j + k
+ end do
+```
+is modelled as a nest of `fir.do_loop` ops such that an outer loop's region
+contains **only** the following:
+ 1. The operations needed to assign/update the outer loop's induction variable.
+ 1. The inner loop itself.
+
+So the MLIR structure for the above example looks similar to the following:
+```
+ fir.do_loop %i_idx = %34 to %36 step %c1 unordered {
+ %i_idx_2 = fir.convert %i_idx : (index) -> i32
+ fir.store %i_idx_2 to %i_iv#1 : !fir.ref<i32>
+
+ fir.do_loop %j_idx = %37 to %39 step %c1_3 unordered {
+ %j_idx_2 = fir.convert %j_idx : (index) -> i32
+ fir.store %j_idx_2 to %j_iv#1 : !fir.ref<i32>
+
+ fir.do_loop %k_idx = %40 to %42 step %c1_5 unordered {
+ %k_idx_2 = fir.convert %k_idx : (index) -> i32
+ fir.store %k_idx_2 to %k_iv#1 : !fir.ref<i32>
+
+ ... loop nest body goes here ...
+ }
+ }
+ }
+```
+This applies to multi-range loops in general; they are represented in the IR as
+a nest of `fir.do_loop` ops with the above nesting structure.
+
+Therefore, the pass detects such "perfectly" nested loop ops to identify multi-range
+loops and map them as "collapsed" loops in OpenMP.
+
+#### Further info regarding loop nest detection
+
+Loop nest detection is currently limited to the scenario described in the previous
+section. However, this is quite limited and can be extended in the future to cover
+more cases. For example, for the following loop nest, even though, both loops are
+perfectly nested; at the moment, only the outer loop is parallelized:
+```fortran
+do concurrent(i=1:n)
+ do concurrent(j=1:m)
+ a(i,j) = i * j
+ end do
+end do
+```
+
+Similarly, for the following loop nest, even though the intervening statement `x = 41`
+does not have any memory effects that would affect parallelization, this nest is
+not parallelized as well (only the outer loop is).
+
+```fortran
+do concurrent(i=1:n)
+ x = 41
+ do concurrent(j=1:m)
+ a(i,j) = i * j
+ end do
+end do
+```
+
+The above also has the consequence that the `j` variable will **not** be
+privatized in the OpenMP parallel/target region. In other words, it will be
+treated as if it was a `shared` variable. For more details about privatization,
+see the "Data environment" section below.
+
+See `flang/test/Transforms/DoConcurrent/loop_nest_test.f90` for more examples
+of what is and is not detected as a perfect loop nest.
+
+<!--
+More details about current status will be added along with relevant parts of the
+implementation in later upstreaming patches.
+-->
+
+## Next steps
+
+This section describes some of the open questions/issues that are not tackled yet
+even in the downstream implementation.
+
+### Delayed privatization
+
+So far, we emit the privatization logic for IVs inline in the parallel/target
+region. This is enough for our purposes right now since we don't
+localize/privatize any sophisticated types of variables yet. Once we have need
+for more advanced localization through `do concurrent`'s locality specifiers
+(see below), delayed privatization will enable us to have a much cleaner IR.
+Once delayed privatization's implementation upstream is supported for the
+required constructs by the pass, we will move to it rather than inlined/early
+privatization.
+
+### Locality specifiers for `do concurrent`
+
+Locality specifiers will enable the user to control the data environment of the
+loop nest in a more fine-grained way. Implementing these specifiers on the
+`FIR` dialect level is needed in order to support this in the
+`DoConcurrentConversionPass`.
+
+Such specifiers will also unlock a potential solution to the
+non-perfectly-nested loops' IVs issue described above. In particular, for a
+non-perfectly nested loop, one middle-ground proposal/solution would be to:
+* Emit the loop's IV as shared/mapped just like we do currently.
+* Emit a warning that the IV of the loop is emitted as shared/mapped.
+* Given support for `LOCAL`, we can recommend the user to explicitly
+ localize/privatize the loop's IV if they choose to.
+
+#### Sharing TableGen clause records from the OpenMP dialect
+
+At the moment, the FIR dialect does not have a way to model locality specifiers
+on the IR level. Instead, something similar to early/eager privatization in OpenMP
+is done for the locality specifiers in `fir.do_loop` ops. Having locality specifier
+modelled in a way similar to delayed privatization (i.e. the `omp.private` op) and
+reductions (i.e. the `omp.declare_reduction` op) can make mapping `do concurrent`
+to OpenMP (and other parallel programming models) much easier.
+
+Therefore, one way to approach this problem is to extract the TableGen records
+for relevant OpenMP clauses in a shared dialect for "data environment management"
+and use these shared records for OpenMP, `do concurrent`, and possibly OpenACC
+as well.
+
+#### Supporting reductions
+
+Similar to locality specifiers, mapping reductions from `do concurrent` to OpenMP
+is also still an open TODO. We can potentially extend the MLIR infrastructure
+proposed in the previous section to share reduction records among the different
+relevant dialects as well.
+
+### More advanced detection of loop nests
+
+As pointed out earlier, any intervening code between the headers of 2 nested
+`do concurrent` loops prevents us from detecting this as a loop nest. In some
+cases this is overly conservative. Therefore, a more flexible detection logic
+of loop nests needs to be implemented.
+
+### Data-dependence analysis
+
+Right now, we map loop nests without analysing whether such mapping is safe to
+do or not. We probably need to at least warn the user of unsafe loop nests due
+to loop-carried dependencies.
+
+### Non-rectangular loop nests
+
+So far, we did not need to use the pass for non-rectangular loop nests. For
+example:
+```fortran
+do concurrent(i=1:n)
+ do concurrent(j=i:n)
+ ...
+ end do
+end do
+```
+We defer this to the (hopefully) near future when we get the conversion in a
+good share for the samples/projects at hand.
+
+### Generalizing the pass to other parallel programming models
+
+Once we have a stable and capable `do concurrent` to OpenMP mapping, we can take
+this in a more generalized direction and allow the pass to target other models;
+e.g. OpenACC. This goal should be kept in mind from the get-go even while only
+targeting OpenMP.
+
+
+## Upstreaming status
+
+- [x] Command line options for `flang` and `bbc`.
+- [x] Conversion pass skeleton (no transormations happen yet).
+- [x] Status description and tracking document (this document).
+- [x] Loop nest detection to identify multi-range loops.
+- [ ] Basic host/CPU mapping support.
+- [ ] Basic device/GPU mapping support.
+- [ ] More advanced host and device support (expaned to multiple items as needed).
diff --git a/flang/docs/index.md b/flang/docs/index.md
index c35f634746e68..913e53d4cfed9 100644
--- a/flang/docs/index.md
+++ b/flang/docs/index.md
@@ -50,6 +50,7 @@ on how to get in touch with us and to learn more about the current status.
DebugGeneration
Directives
DoConcurrent
+ DoConcurrentConversionToOpenMP
Extensions
F202X
FIRArrayOperations
diff --git a/flang/include/flang/Frontend/CodeGenOptions.def b/flang/include/flang/Frontend/CodeGenOptions.def
index deb8d1aede518..13cda965600b5 100644
--- a/flang/include/flang/Frontend/CodeGenOptions.def
+++ b/flang/include/flang/Frontend/CodeGenOptions.def
@@ -41,5 +41,7 @@ ENUM_CODEGENOPT(DebugInfo, llvm::codegenoptions::DebugInfoKind, 4, llvm::codeg
ENUM_CODEGENOPT(VecLib, llvm::driver::VectorLibrary, 3, llvm::driver::VectorLibrary::NoLibrary) ///< Vector functions library to use
ENUM_CODEGENOPT(FramePointer, llvm::FramePointerKind, 2, llvm::FramePointerKind::None) ///< Enable the usage of frame pointers
+ENUM_CODEGENOPT(DoConcurrentMapping, DoConcurrentMappingKind, 2, DoConcurrentMappingKind::DCMK_None) ///< Map `do concurrent` to OpenMP
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
diff --git a/flang/include/flang/Frontend/CodeGenOptions.h b/flang/include/flang/Frontend/CodeGenOptions.h
index f19943335737b..23d99e1f0897a 100644
--- a/flang/include/flang/Frontend/CodeGenOptions.h
+++ b/flang/include/flang/Frontend/CodeGenOptions.h
@@ -15,6 +15,7 @@
#ifndef FORTRAN_FRONTEND_CODEGENOPTIONS_H
#define FORTRAN_FRONTEND_CODEGENOPTIONS_H
+#include "flang/Optimizer/OpenMP/Utils.h"
#include "llvm/Frontend/Debug/Options.h"
#include "llvm/Frontend/Driver/CodeGenOptions.h"
#include "llvm/Support/CodeGen.h"
@@ -143,6 +144,10 @@ class CodeGenOptions : public CodeGenOptionsBase {
/// (-mlarge-data-threshold).
uint64_t LargeDataThreshold;
+ /// Optionally map `do concurrent` loops to OpenMP. This is only valid of
+ /// OpenMP is enabled.
+ using DoConcurrentMappingKind = flangomp::DoConcurrentMappingKind;
+
// Define accessors/mutators for code generation options of enumeration type.
#define CODEGENOPT(Name, Bits, Default)
#define ENUM_CODEGENOPT(Name, Type, Bits, Default) \
diff --git a/flang/include/flang/Optimizer/OpenMP/Passes.h b/flang/include/flang/Optimizer/OpenMP/Passes.h
index feb395f1a12db..c67bddbcd2704 100644
--- a/flang/include/flang/Optimizer/OpenMP/Passes.h
+++ b/flang/include/flang/Optimizer/OpenMP/Passes.h
@@ -13,6 +13,7 @@
#ifndef FORTRAN_OPTIMIZER_OPENMP_PASSES_H
#define FORTRAN_OPTIMIZER_OPENMP_PASSES_H
+#include "flang/Optimizer/OpenMP/Utils.h"
#include "mlir/Dialect/Func/IR/FuncOps.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/Pass/Pass.h"
@@ -30,6 +31,7 @@ namespace flangomp {
/// divided into units of work.
bool shouldUseWorkshareLowering(mlir::Operation *op);
+std::unique_ptr<mlir::Pass> createDoConcurrentConversionPass(bool mapToDevice);
} // namespace flangomp
#endif // FORTRAN_OPTIMIZER_OPENMP_PASSES_H
diff --git a/flang/include/flang/Optimizer/OpenMP/Passes.td b/flang/include/flang/Optimizer/OpenMP/Passes.td
index 3add0c560f88d..fcc7a4ca31fef 100644
--- a/flang/include/flang/Optimizer/OpenMP/Passes.td
+++ b/flang/include/flang/Optimizer/OpenMP/Passes.td
@@ -50,6 +50,36 @@ def FunctionFilteringPass : Pass<"omp-function-filtering"> {
];
}
+def DoConcurrentConversionPass : Pass<"omp-do-concurrent-conversion", "mlir::func::FuncOp"> {
+ let summary = "Map `DO CONCURRENT` loops to OpenMP worksharing loops.";
+
+ let description = [{ This is an experimental pass to map `DO CONCURRENT` loops
+ to their correspnding equivalent OpenMP worksharing constructs.
+
+ For now the following is supported:
+ - Mapping simple loops to `parallel do`.
+
+ Still TODO:
+ - More extensive testing.
+ }];
+
+ let dependentDialects = ["mlir::omp::OpenMPDialect"];
+
+ let options = [
+ Option<"mapTo", "map-to",
+ "flangomp::DoConcurrentMappingKind",
+ /*default=*/"flangomp::DoConcurrentMappingKind::DCMK_None",
+ "Try to map `do concurrent` loops to OpenMP [none|host|device]",
+ [{::llvm::cl::values(
+ clEnumValN(flangomp::DoConcurrentMappingKind::DCMK_None,
+ "none", "Do not lower `do concurrent` to OpenMP"),
+ clEnumValN(flangomp::DoConcurrentMappingKind::DCMK_Host,
+ "host", "Lower to run in parallel on the CPU"),
+ clEnumValN(flangomp::DoConcurrentMappingKind::DCMK_Device,
+ "device", "Lower to run in parallel on the GPU")
+ )}]>,
+ ];
+}
// Needs to be scheduled on Module as we create functions in it
def LowerWorkshare : Pass<"lower-workshare", "::mlir::ModuleOp"> {
diff --git a/flang/include/flang/Optimizer/OpenMP/Utils.h b/flang/include/flang/Optimizer/OpenMP/Utils.h
new file mode 100644
index 0000000000000..636c768b016b7
--- /dev/null
+++ b/flang/include/flang/Optimizer/OpenMP/Utils.h
@@ -0,0 +1,26 @@
+//===-- Optimizer/OpenMP/Utils.h --------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_OPTIMIZER_OPENMP_UTILS_H
+#define FORTRAN_OPTIMIZER_OPENMP_UTILS_H
+
+namespace flangomp {
+
+enum class DoConcurrentMappingKind {
+ DCMK_None, ///< Do not lower `do concurrent` to OpenMP.
+ DCMK_Host, ///< Lower to run in parallel on the CPU.
+ DCMK_Device ///< Lower to run in parallel on the GPU.
+};
+
+} // namespace flangomp
+
+#endif // FORTRAN_OPTIMIZER_OPENMP_UTILS_H
diff --git a/flang/include/flang/Optimizer/Passes/Pipelines.h b/flang/include/flang/Optimizer/Passes/Pipelines.h
index ef5d44ded706c..a3f59ee8dd013 100644
--- a/flang/include/flang/Optimizer/Passes/Pipelines.h
+++ b/flang/include/flang/Optimizer/Passes/Pipelines.h
@@ -128,6 +128,17 @@ void createHLFIRToFIRPassPipeline(
mlir::PassManager &pm, bool enableOpenMP,
llvm::OptimizationLevel optLevel = defaultOptLevel);
+struct OpenMPFIRPassPipelineOpts {
+ /// Whether code is being generated for a target device rather than the host
+ /// device
+ bool isTargetDevice;
+
+ /// Controls how to map `do concurrent` loops; to device, host, or none at
+ /// all.
+ Fortran::frontend::CodeGenOptions::DoConcurrentMappingKind
+ doConcurrentMappingKind;
+};
+
/// Create a pass pipeline for handling certain OpenMP transformations needed
/// prior to FIR lowering.
///
@@ -135,9 +146,10 @@ void createHLFIRToFIRPassPipeline(
/// that the FIR is correct with respect to OpenMP operations/attributes.
///
/// \param pm - MLIR pass manager that will hold the pipeline definition.
-/// \param isTargetDevice - Whether code is being generated for a target device
-/// rather than the host device.
-void createOpenMPFIRPassPipeline(mlir::PassManager &pm, bool isTargetDevice);
+/// \param opts - options to control OpenMP code-gen; see struct docs for more
+/// details.
+void createOpenMPFIRPassPipeline(mlir::PassManager &pm,
+ OpenMPFIRPassPipelineOpts opts);
#if !defined(FLANG_EXCLUDE_CODEGEN)
void createDebugPasses(mlir::PassManager &pm,
diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index f3d9432c62d3b..809e423f5aae9 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -157,6 +157,32 @@ static bool parseDebugArgs(Fortran::frontend::CodeGenOptions &opts,
return true;
}
+static void parseDoConcurrentMapping(Fortran::frontend::CodeGenOptions &opts,
+ llvm::opt::ArgList &args,
+ clang::DiagnosticsEngine &diags) {
+ llvm::opt::Arg *arg =
+ args.getLastArg(clang::driver::options::OPT_fdo_concurrent_to_openmp_EQ);
+ if (!arg)
+ return;
+
+ using DoConcurrentMappingKind =
+ Fortran::frontend::CodeGenOptions::DoConcurrentMappingKind;
+ std::optional<DoConcurrentMappingKind> val =
+ llvm::StringSwitch<std::optional<DoConcurrentMappingKind>>(
+ arg->getValue())
+ .Case("none", DoConcurrentMappingKind::DCMK_None)
+ .Case("host", DoConcurrentMappingKind::DCMK_Host)
+ .Case("device", DoConcurrentMappingKind::DCMK_Device)
+ .Default(std::nullopt);
+
+ if (!val.has_value()) {
+ diags.Report(clang::diag::err_drv_invalid_value)
+ << arg->getAsString(args) << arg->getValue();
+ }
+
+ opts.setDoConcurrentMapping(val.value());
+}
+
static bool parseVectorLibArg(Fortran::frontend::CodeGenOptions &opts,
llvm::opt::ArgList &args,
clang::DiagnosticsEngine &diags) {
@@ -426,6 +452,8 @@ static void parseCodeGenArgs(Fortran::frontend::CodeGenOptions &opts,
clang::driver::options::OPT_funderscoring, false)) {
opts.Underscoring = 0;
}
+
+ parseDoConcurrentMapping(opts, args, diags);
}
/// Parses all target input arguments and populates the target
diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
index 763c810ace0eb..ccc8c7d96135f 100644
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cp...
[truncated]
|
This was referenced Feb 17, 2025
|
Abandoned in favor of #127595. |
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Mar 27, 2025
…27595) Upstreams the next part of do concurrent to OpenMP mapping pass (from AMD's ROCm implementation). See llvm#126026 for more context. This PR add loop nest detection logic. This enables us to discover muli-range do concurrent loops and then map them as "collapsed" loop nests to OpenMP. This is a follow up for llvm#126026, only the latest commit is relevant. This is a replacement for llvm#127478 using a `/user/<username>/<branchname>` branch. PR stack: - llvm#126026 - llvm#127595 (this PR) - llvm#127633 - llvm#127634 - llvm#127635
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Apr 2, 2025
Upstreams the next part of do concurrent to OpenMP mapping pass (from AMD's ROCm implementation). See #126026 for more context. This PR add loop nest detection logic. This enables us to discover muli-range do concurrent loops and then map them as "collapsed" loop nests to OpenMP. This is a follow up for #126026, only the latest commit is relevant. This is a replacement for #127478 using a `/user/<username>/<branchname>` branch. PR stack: - #126026 - #127595 (this PR) - #127633 - #127634 - #127635
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…on. (#127595) Upstreams the next part of do concurrent to OpenMP mapping pass (from AMD's ROCm implementation). See llvm/llvm-project#126026 for more context. This PR add loop nest detection logic. This enables us to discover muli-range do concurrent loops and then map them as "collapsed" loop nests to OpenMP. This is a follow up for llvm/llvm-project#126026, only the latest commit is relevant. This is a replacement for llvm/llvm-project#127478 using a `/user/<username>/<branchname>` branch. PR stack: - llvm/llvm-project#126026 - llvm/llvm-project#127595 (this PR) - llvm/llvm-project#127633 - llvm/llvm-project#127634 - llvm/llvm-project#127635
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Upstreams the next part of
do concurrentto OpenMP mapping pass (fromAMD's ROCm implementation). See #126026 for more context.
This PR add loop nest detection logic. This enables us to discover
muli-range
do concurrentloops and then map them as "collapsed" loopnests to OpenMP.
This is a follow up for #126026, only the latest commit is relevant.