[csa] Add IsIntPtrOrSmiConstantZero to detect and optimize constant zero values

Review-Url: https://codereview.chromium.org/2658253002
Cr-Commit-Position: refs/heads/master@{#42766}

src/code-stub-assembler.cc

@@ -171,6 +171,16 @@ Node* CodeStubAssembler::IntPtrOrSmiConstant(int value, ParameterMode mode) {
   }
 }
 
+bool CodeStubAssembler::IsIntPtrOrSmiConstantZero(Node* test) {
+  int32_t constant_test;
+  Smi* smi_test;
+  if ((ToInt32Constant(test, constant_test) && constant_test == 0) ||
+      (ToSmiConstant(test, smi_test) && smi_test->value() == 0)) {
+    return true;
+  }
+  return false;
+}
+
 Node* CodeStubAssembler::IntPtrRoundUpToPowerOfTwo32(Node* value) {
   Comment("IntPtrRoundUpToPowerOfTwo32");
   CSA_ASSERT(this, UintPtrLessThanOrEqual(value, IntPtrConstant(0x80000000u)));
@@ -2062,8 +2072,7 @@ Node* CodeStubAssembler::AllocateJSArray(ElementsKind kind, Node* array_map,
                                          Node* allocation_site,
                                          ParameterMode capacity_mode) {
   Node *array = nullptr, *elements = nullptr;
-  int32_t constant_capacity;
-  if (ToInt32Constant(capacity, constant_capacity) && constant_capacity == 0) {
+  if (IsIntPtrOrSmiConstantZero(capacity)) {
     // Array is empty. Use the shared empty fixed array instead of allocating a
     // new one.
     array = AllocateUninitializedJSArrayWithoutElements(kind, array_map, length,

src/code-stub-assembler.h

@@ -140,6 +140,8 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
 
   Node* IntPtrOrSmiConstant(int value, ParameterMode mode);
 
+  bool IsIntPtrOrSmiConstantZero(Node* test);
+
   // Round the 32bits payload of the provided word up to the next power of two.
   Node* IntPtrRoundUpToPowerOfTwo32(Node* value);
   // Select the maximum of the two provided IntPtr values.