Changeset 59056 in webkit for trunk/JavaScriptCore/jit/JITPropertyAccess32_64.cpp

Timestamp:

May 9, 2010, 4:42:22 AM (15 years ago)

Author:

[email protected]

Message:

2010-05-09 Oliver Hunt <​[email protected]>

Reviewed by Maciej Stachowiak.

Improve string indexing performance
​https://bugs.webkit.org/show_bug.cgi?id=38814

Add an assembly stub to do indexed loads from strings much
more cheaply than the current stub dispatch logic. We can
do this because we are able to make guarantees about the
register contents when entering the stub so the call overhead
is negligible.

• jit/JIT.h:
• jit/JITInlineMethods.h:
• jit/JITOpcodes.cpp:
• jit/JITPropertyAccess.cpp: (JSC::JIT::stringGetByValStubGenerator): (JSC::JIT::emitSlow_op_get_by_val):

Moved from JITOpcodes.cpp to keep the slowcase next to
the normal case codegen as we do for everything else.

• jit/JITPropertyAccess32_64.cpp: (JSC::JIT::stringGetByValStubGenerator): (JSC::JIT::emitSlow_op_get_by_val):
• jit/JSInterfaceJIT.h: (JSC::JSInterfaceJIT::emitFastArithImmToInt):

File:

• trunk/JavaScriptCore/jit/JITPropertyAccess32_64.cpp (modified) (2 diffs)

trunk/JavaScriptCore/jit/JITPropertyAccess32_64.cpp

@@ -270 +270 @@
 #endif
 
+PassRefPtr<NativeExecutable> JIT::stringGetByValStubGenerator(JSGlobalData* globalData, ExecutablePool* pool)
+{
+    JSInterfaceJIT jit;
+    JumpList failures;
+    failures.append(jit.branchPtr(NotEqual, Address(regT0), ImmPtr(globalData->jsStringVPtr)));
+    failures.append(jit.branchTest32(NonZero, Address(regT0, OBJECT_OFFSETOF(JSString, m_fiberCount))));
+    
+    // Load string length to regT1, and start the process of loading the data pointer into regT0
+    jit.load32(Address(regT0, ThunkHelpers::jsStringLengthOffset()), regT1);
+    jit.loadPtr(Address(regT0, ThunkHelpers::jsStringValueOffset()), regT0);
+    jit.loadPtr(Address(regT0, ThunkHelpers::stringImplDataOffset()), regT0);
+    
+    // Do an unsigned compare to simultaneously filter negative indices as well as indices that are too large
+    failures.append(jit.branch32(AboveOrEqual, regT2, regT1));
+    
+    // Load the character
+    jit.load16(BaseIndex(regT0, regT2, TimesTwo, 0), regT0);
+    
+    failures.append(jit.branch32(AboveOrEqual, regT0, Imm32(0x100)));
+    jit.move(ImmPtr(globalData->smallStrings.singleCharacterStrings()), regT1);
+    jit.loadPtr(BaseIndex(regT1, regT0, ScalePtr, 0), regT0);
+    jit.move(Imm32(JSValue::CellTag), regT1); // We null check regT0 on return so this is safe
+    jit.ret();
+
+    failures.link(&jit);
+    jit.move(Imm32(0), regT0);
+    jit.ret();
+    
+    LinkBuffer patchBuffer(&jit, pool);
+    return adoptRef(new NativeExecutable(patchBuffer.finalizeCode()));
+}
+
 void JIT::emit_op_get_by_val(Instruction* currentInstruction)
 {
@@ -301 +333 @@
     linkSlowCase(iter); // property int32 check
     linkSlowCaseIfNotJSCell(iter, base); // base cell check
+
+    Jump nonCell = jump();
     linkSlowCase(iter); // base array check
+    Jump notString = branchPtr(NotEqual, Address(regT0), ImmPtr(m_globalData->jsStringVPtr));
+    emitNakedCall(m_globalData->getThunk(stringGetByValStubGenerator)->generatedJITCode().addressForCall());
+    Jump failed = branchTestPtr(Zero, regT0);
+    emitStore(dst, regT1, regT0);
+    emitJumpSlowToHot(jump(), OPCODE_LENGTH(op_get_by_val));
+    failed.link(this);
+    notString.link(this);
+    nonCell.link(this);
+
     linkSlowCase(iter); // vector length check
     linkSlowCase(iter); // empty value