Changeset 262562 in webkit for trunk/Source/JavaScriptCore/ftl/FTLOSRExitCompiler.cpp

Timestamp:

Jun 4, 2020, 12:54:17 PM (5 years ago)

Author:

[email protected]

Message:

Reduce DFGDoesGCCheck to only storing a uint32_t.
​https://bugs.webkit.org/show_bug.cgi?id=212734

Reviewed by Saam Barati and Caio Lima.

This patch changes the encoding of DoesGCCheck so that it will fit better in a
uint32_t. This has the following benefits:

1. speed improvement for debug builds because it now takes less instructions (especially in JITted code) to store to DoesGCCheck::m_value.
2. enables this check for 32-bit platforms as well.

Fun fact: we currently have 373 DFG::NodeTypes. Hence, 9 bits for nodeOp.

The new encoding provides 21 bis for the nodeIndex. This gives us up to 2097152
node indexes. In my experience, I've never seen more than 3 decimal digits for
the nodeIndex so far. If we ever find that we need more than 21 bits of nodeIndex,
we have 2 options to deal with it:

1. We can just ignore the high bits. After all, it is the nodeOp that is the most interesting piece of data we need to debug doesGC issues.

2. We can make DoesGCCheck use uint64_t for storage. This encoding automatically scales to 64-bit, while still allowing the more efficient form of storing a 32-bit immediate to be used for the common cases.

This patch also makes ENABLE_DFG_DOES_GC_VALIDATION dependent on ENABLE(DFG_JIT).
DoesGC is only relevant for the DFG and FTL JITs.

• dfg/DFGDoesGCCheck.cpp:

(JSC::DFG::DoesGCCheck::verifyCanGC):

• dfg/DFGDoesGCCheck.h:

(JSC::DFG::DoesGCCheck::encode):
(JSC::DFG::DoesGCCheck::expectDoesGC const):
(JSC::DFG::DoesGCCheck::isSpecial const):
(JSC::DFG::DoesGCCheck::special):
(JSC::DFG::DoesGCCheck::nodeOp):
(JSC::DFG::DoesGCCheck::nodeIndex):
(JSC::DFG::DoesGCCheck::expectDoesGC): Deleted.
(JSC::DFG::DoesGCCheck::isSpecial): Deleted.
(JSC::DFG::DoesGCCheck::specialIndex): Deleted.
(JSC::DFG::DoesGCCheck::bits): Deleted.

• dfg/DFGNodeType.h:
• dfg/DFGOSRExit.cpp:

(JSC::DFG::OSRExit::compileExit):

• dfg/DFGSpeculativeJIT32_64.cpp:

(JSC::DFG::SpeculativeJIT::compile):

• dfg/DFGSpeculativeJIT64.cpp:

(JSC::DFG::SpeculativeJIT::compile):

• ftl/FTLLowerDFGToB3.cpp:

(JSC::FTL::DFG::LowerDFGToB3::compileNode):

• ftl/FTLOSRExitCompiler.cpp:

(JSC::FTL::compileStub):

• heap/Heap.h:

File:

• trunk/Source/JavaScriptCore/ftl/FTLOSRExitCompiler.cpp (modified) (1 diff)

trunk/Source/JavaScriptCore/ftl/FTLOSRExitCompiler.cpp

@@ -216 +216 @@
         // we exit from this site, but all subsequent exits will take this compiled
         // ramp without calling compileFTLOSRExit() first.
-        jit.store64(CCallHelpers::TrustedImm64(DoesGCCheck::encode(true, DoesGCCheck::Special::FTLOSRExit)), vm.heap.addressOfDoesGC());
+        jit.store32(CCallHelpers::TrustedImm32(DoesGCCheck::encode(true, DoesGCCheck::Special::FTLOSRExit)), vm.heap.addressOfDoesGC());
     }