Changeset 38377 in webkit

Timestamp:

Nov 13, 2008 2:27:59 PM (15 years ago)

Author:

cwzwarich@webkit.org

Message:

2008-11-13 Cameron Zwarich <​zwarich@apple.com>

Reviewed by Darin Adler.

Bug 22238: Avoid unnecessary reads of temporaries when the target machine register is not eax
<​https://bugs.webkit.org/show_bug.cgi?id=22238>

Enable the optimization of not reading a value back from memory that we
just wrote when the target machine register is not eax. In order to do
this, the code generation for op_put_global_var must be changed to
read its argument into a register before overwriting eax.

This is a 0.5% speedup on SunSpider and shows no change on the V8
benchmark suite when run in either harness.

• VM/CTI.cpp: (JSC::CTI::emitGetArg): (JSC::CTI::privateCompileMainPass):

Location:

trunk/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• VM/CTI.cpp (modified) (3 diffs)

trunk/JavaScriptCore/ChangeLog

@@ +1 @@
+2008-11-13  Cameron Zwarich  <zwarich@apple.com>
+
+        Reviewed by Darin Adler.
+
+        Bug 22238: Avoid unnecessary reads of temporaries when the target machine register is not eax
+        <https://bugs.webkit.org/show_bug.cgi?id=22238>
+
+        Enable the optimization of not reading a value back from memory that we
+        just wrote when the target machine register is not eax. In order to do
+        this, the code generation for op_put_global_var must be changed to
+        read its argument into a register before overwriting eax.
+
+        This is a 0.5% speedup on SunSpider and shows no change on the V8
+        benchmark suite when run in either harness.
+
+        * VM/CTI.cpp:
+        (JSC::CTI::emitGetArg):
+        (JSC::CTI::privateCompileMainPass):
+
 2008-11-13  Cameron Zwarich  <zwarich@apple.com>
 

trunk/JavaScriptCore/VM/CTI.cpp

@@ -190 +190 @@
     }
 
-    if (src == m_lastResultBytecodeRegister && dst == X86::eax && m_codeBlock->isTemporaryRegisterIndex(src)) {
+    if (src == m_lastResultBytecodeRegister && m_codeBlock->isTemporaryRegisterIndex(src)) {
         bool atJumpTarget = false;
         while (m_jumpTargetsPosition < m_codeBlock->jumpTargets.size() && m_codeBlock->jumpTargets[m_jumpTargetsPosition] <= currentInstructionIndex) {
@@ -200 +200 @@
         if (!atJumpTarget) {
             // The argument we want is already stored in eax
+            if (dst != X86::eax)
+                m_jit.movl_rr(X86::eax, dst);
             killLastResultRegister();
             return;
@@ -1386 +1388 @@
         }
         case op_put_global_var: {
+            emitGetArg(instruction[i + 3].u.operand, X86::edx, i);
             JSVariableObject* globalObject = static_cast<JSVariableObject*>(instruction[i + 1].u.jsCell);
             m_jit.movl_i32r(asInteger(globalObject), X86::eax);
-            emitGetArg(instruction[i + 3].u.operand, X86::edx, i);
             emitPutVariableObjectRegister(X86::edx, X86::eax, instruction[i + 2].u.operand);
             i += 4;