Tweak SmiSub for X64

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 96fa4fc49630424093eaa29874c118e95c34a115..6a7ca602a3e8d24f5e9eacbf9a74b705dd2c8f95 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -1699,34 +1699,37 @@ void MacroAssembler::SmiAdd(Register dst,
 }
 
 
-void MacroAssembler::SmiSub(Register dst,
-                            Register src1,
-                            Register src2,
-                            Label* on_not_smi_result,
-                            Label::Distance near_jump) {
-  ASSERT_NOT_NULL(on_not_smi_result);
-  ASSERT(!dst.is(src2));
+template<class T>
+static void SmiSubHelper(MacroAssembler* masm,
+                         Register dst,
+                         Register src1,
+                         T src2,
+                         Label* on_not_smi_result,
+                         Label::Distance near_jump) {
   if (dst.is(src1)) {
-    cmpq(dst, src2);
-    j(overflow, on_not_smi_result, near_jump);
-    subq(dst, src2);
+    Label done;
+    masm->subq(dst, src2);
+    masm->j(no_overflow, &done, Label::kNear);
+    // Restore src1.
+    masm->addq(dst, src2);
+    masm->jmp(on_not_smi_result, near_jump);
+    masm->bind(&done);
   } else {
-    movq(dst, src1);
-    subq(dst, src2);
-    j(overflow, on_not_smi_result, near_jump);
+    masm->movq(dst, src1);
+    masm->subq(dst, src2);
+    masm->j(overflow, on_not_smi_result, near_jump);
   }
 }
 
 
-void MacroAssembler::SmiSub(Register dst, Register src1, Register src2) {
-  // No overflow checking. Use only when it's known that
-  // overflowing is impossible (e.g., subtracting two positive smis).
+void MacroAssembler::SmiSub(Register dst,
+                            Register src1,
+                            Register src2,
+                            Label* on_not_smi_result,
+                            Label::Distance near_jump) {
+  ASSERT_NOT_NULL(on_not_smi_result);
   ASSERT(!dst.is(src2));
-  if (!dst.is(src1)) {
-    movq(dst, src1);
-  }
-  subq(dst, src2);
-  Assert(no_overflow, kSmiSubtractionOverflow);
+  SmiSubHelper<Register>(this, dst, src1, src2, on_not_smi_result, near_jump);
 }
 
 
@@ -1736,29 +1739,36 @@ void MacroAssembler::SmiSub(Register dst,
                             Label* on_not_smi_result,
                             Label::Distance near_jump) {
   ASSERT_NOT_NULL(on_not_smi_result);
-  if (dst.is(src1)) {
-    movq(kScratchRegister, src2);
-    cmpq(src1, kScratchRegister);
-    j(overflow, on_not_smi_result, near_jump);
-    subq(src1, kScratchRegister);
-  } else {
-    movq(dst, src1);
-    subq(dst, src2);
-    j(overflow, on_not_smi_result, near_jump);
-  }
+  ASSERT(!src2.AddressUsesRegister(dst));
+  SmiSubHelper<Operand>(this, dst, src1, src2, on_not_smi_result, near_jump);
 }
 
 
-void MacroAssembler::SmiSub(Register dst,
-                            Register src1,
-                            const Operand& src2) {
+template<class T>
+static void SmiSubNoOverflowHelper(MacroAssembler* masm,
+                                   Register dst,
+                                   Register src1,
+                                   T src2) {
   // No overflow checking. Use only when it's known that
   // overflowing is impossible (e.g., subtracting two positive smis).
   if (!dst.is(src1)) {
-    movq(dst, src1);
+    masm->movq(dst, src1);
   }
-  subq(dst, src2);
-  Assert(no_overflow, kSmiSubtractionOverflow);
+  masm->subq(dst, src2);
+  masm->Assert(no_overflow, kSmiSubtractionOverflow);
+}
+
+
+void MacroAssembler::SmiSub(Register dst, Register src1, Register src2) {
+  ASSERT(!dst.is(src2));
+  SmiSubNoOverflowHelper<Register>(this, dst, src1, src2);
+}
+
+
+void MacroAssembler::SmiSub(Register dst,
+                            Register src1,
+                            const Operand& src2) {
+  SmiSubNoOverflowHelper<Operand>(this, dst, src1, src2);
 }