Improve code generation for bounds checks.

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index cb15e0d82f4872f7b3bbc1608cf5d49c90126f22..f61fd9aae22293f46ccc5c70986531b3bc24a34e 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -1865,9 +1865,16 @@ LInstruction* LChunkBuilder::DoSeqStringSetChar(HSeqStringSetChar* instr) {
 
 
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
-  return AssignEnvironment(new(zone()) LBoundsCheck(
-      UseRegisterOrConstantAtStart(instr->index()),
-      UseAtStart(instr->length())));
+  if (!FLAG_debug_code && instr->skip_check()) return NULL;
+  LOperand* index = UseRegisterOrConstantAtStart(instr->index());
+  LOperand* length = !index->IsConstantOperand()
+      ? UseOrConstantAtStart(instr->length())
+      : UseAtStart(instr->length());
+  LInstruction* result = new(zone()) LBoundsCheck(index, length);
+  if (!FLAG_debug_code || !instr->skip_check()) {
+    result = AssignEnvironment(result);
+  }
+  return result;
 }