Bug 818138 - On x64 optimize push with small pointer immediates. r=jandem

js/src/ion/IonMacroAssembler.h

@@ -492,7 +492,7 @@ class MacroAssembler : public MacroAssemblerSpecific
         // Push VMFunction pointer, to mark arguments.
         Push(ImmWord(f));
     }
-    void enterFakeExitFrame(void *codeVal = NULL) {
+    void enterFakeExitFrame(IonCode *codeVal = NULL) {
         linkExitFrame();
         Push(ImmWord(uintptr_t(codeVal)));
         Push(ImmWord(uintptr_t(NULL)));

js/src/ion/x64/Assembler-x64.h

@@ -289,8 +289,14 @@ class Assembler : public AssemblerX86Shared
         push(ScratchReg);
     }
     void push(const ImmWord ptr) {
-        movq(ptr, ScratchReg);
-        push(ScratchReg);
+        // We often end up with ImmWords that actually fit into int32.
+        // Be aware of the sign extension behavior.
+        if (ptr.value <= INT32_MAX) {
+            push(Imm32(ptr.value));
+        } else {
+            movq(ptr, ScratchReg);
+            push(ScratchReg);
+        }
     }
     void push(const FloatRegister &src) {
         subq(Imm32(sizeof(void*)), StackPointer);