MIPS: Improve code generation for bounds checks.

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index a5fed5fa682d11929f9ba5d846cfad72602aafeb..0bfe7d2e269c6508f01bee9c8b8133c7b8601b57 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -1782,9 +1782,16 @@ LInstruction* LChunkBuilder::DoSeqStringSetChar(HSeqStringSetChar* instr) {
 
 
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
-  LOperand* value = UseRegisterOrConstantAtStart(instr->index());
-  LOperand* length = UseRegister(instr->length());
-  return AssignEnvironment(new(zone()) LBoundsCheck(value, length));
+  if (!FLAG_debug_code && instr->skip_check()) return NULL;
+  LOperand* index = UseRegisterOrConstantAtStart(instr->index());
+  LOperand* length = !index->IsConstantOperand()
+  ? UseRegisterOrConstantAtStart(instr->length())
+  : UseRegisterAtStart(instr->length());
+  LInstruction* result = new(zone()) LBoundsCheck(index, length);
+  if (!FLAG_debug_code || !instr->skip_check()) {
+    result = AssignEnvironment(result);
+  }
+  return result;
 }