Changeset 35703 in webkit for trunk/JavaScriptCore/VM/CodeGenerator.cpp

Timestamp:

Aug 12, 2008, 8:17:19 PM (17 years ago)

Author:

[email protected]

Message:

Add peephole optimisation to 'op_not... jfalse...' (eg. if(!...) )

Reviewed by Geoff Garen

This is a very slight win in sunspider, and a fairly substantial win
in hot code that does if(!...), etc.

File:

• trunk/JavaScriptCore/VM/CodeGenerator.cpp (modified) (2 diffs)

trunk/JavaScriptCore/VM/CodeGenerator.cpp

@@ -434 +434 @@
 }
 
+void CodeGenerator::retrieveLastUnaryOp(int& dstIndex, int& srcIndex)
+{
+    ASSERT(instructions().size() >= 3);
+    size_t size = instructions().size();
+    dstIndex = instructions().at(size - 2).u.operand;
+    srcIndex = instructions().at(size - 1).u.operand;
+}
+
 void ALWAYS_INLINE CodeGenerator::rewindBinaryOp()
 {
     ASSERT(instructions().size() >= 4);
     instructions().shrink(instructions().size() - 4);
+}
+
+void ALWAYS_INLINE CodeGenerator::rewindUnaryOp()
+{
+    ASSERT(instructions().size() >= 3);
+    instructions().shrink(instructions().size() - 3);
 }
 
@@ -491 +505 @@
             return target;
         }
+    } else if (m_lastOpcodeID == op_not) {
+        int dstIndex;
+        int srcIndex;
+
+        retrieveLastUnaryOp(dstIndex, srcIndex);
+
+        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
+            rewindUnaryOp();
+            emitOpcode(target->isForwardLabel() ? op_jtrue : op_loop_if_true);
+            instructions().append(srcIndex);
+            instructions().append(target->offsetFrom(instructions().size()));
+            return target;
+        }        
     }