[stubs] Suppress shift by zero.

LOG=N
BUG=

Review-Url: https://codereview.chromium.org/2157363003
Cr-Commit-Position: refs/heads/master@{#37886}

src/code-stub-assembler.cc

@@ -1770,7 +1770,7 @@ Node* CodeStubAssembler::StringFromCharCode(Node* code) {
 Node* CodeStubAssembler::BitFieldDecode(Node* word32, uint32_t shift,
                                         uint32_t mask) {
   return Word32Shr(Word32And(word32, Int32Constant(mask)),
-                   Int32Constant(shift));
+                   static_cast<int>(shift));
 }
 
 void CodeStubAssembler::SetCounter(StatsCounter* counter, int value) {

src/compiler/code-assembler.cc

@@ -209,11 +209,18 @@ CODE_ASSEMBLER_BINARY_OP_LIST(DEFINE_CODE_ASSEMBLER_BINARY_OP)
 #undef DEFINE_CODE_ASSEMBLER_BINARY_OP
 
 Node* CodeAssembler::WordShl(Node* value, int shift) {
-  return raw_assembler_->WordShl(value, IntPtrConstant(shift));
+  return (shift != 0) ? raw_assembler_->WordShl(value, IntPtrConstant(shift))
+                      : value;
 }
 
 Node* CodeAssembler::WordShr(Node* value, int shift) {
-  return raw_assembler_->WordShr(value, IntPtrConstant(shift));
+  return (shift != 0) ? raw_assembler_->WordShr(value, IntPtrConstant(shift))
+                      : value;
+}
+
+Node* CodeAssembler::Word32Shr(Node* value, int shift) {
+  return (shift != 0) ? raw_assembler_->Word32Shr(value, IntPtrConstant(shift))
+                      : value;
 }
 
 Node* CodeAssembler::ChangeUint32ToWord(Node* value) {

src/compiler/code-assembler.h

@@ -285,6 +285,7 @@ class CodeAssembler {
 
   Node* WordShl(Node* value, int shift);
   Node* WordShr(Node* value, int shift);
+  Node* Word32Shr(Node* value, int shift);
 
 // Unary
 #define DECLARE_CODE_ASSEMBLER_UNARY_OP(name) Node* name(Node* a);