[codegen] Remove redundant xorpd instructions

It seems like they were originally added in https://crrev.com/23654026
(Sep 2013) to break dependences in the OOO pipeline. This code pattern
was then later copied for other instructions too
(https://crrev.com/1424333002).
The reason for the xorpd is not mentioned in the code though, and I
found no other compiler doing this. So maybe it's obsolete by now, and
only increases code size.

Let's remove them and see if we get any performance regressions.

R=ahaas@chromium.org
CC=yangguo@chromium.org

Change-Id: I0e6d65afa67f0ee286e5b0ba95c91092c5261c8f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1926427Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65077}

src/codegen/ia32/macro-assembler-ia32.cc

@@ -511,12 +511,10 @@ void MacroAssembler::MaybeDropFrames() {
 }
 
 void TurboAssembler::Cvtsi2ss(XMMRegister dst, Operand src) {
-  xorps(dst, dst);
   cvtsi2ss(dst, src);
 }
 
 void TurboAssembler::Cvtsi2sd(XMMRegister dst, Operand src) {
-  xorpd(dst, dst);
   cvtsi2sd(dst, src);
 }
 

src/codegen/x64/macro-assembler-x64.cc

@@ -736,10 +736,8 @@ void TurboAssembler::Cvtsd2ss(XMMRegister dst, Operand src) {
 void TurboAssembler::Cvtlsi2sd(XMMRegister dst, Register src) {
   if (CpuFeatures::IsSupported(AVX)) {
     CpuFeatureScope scope(this, AVX);
-    vxorpd(dst, dst, dst);
     vcvtlsi2sd(dst, dst, src);
   } else {
-    xorpd(dst, dst);
     cvtlsi2sd(dst, src);
   }
 }
@@ -747,10 +745,8 @@ void TurboAssembler::Cvtlsi2sd(XMMRegister dst, Register src) {
 void TurboAssembler::Cvtlsi2sd(XMMRegister dst, Operand src) {
   if (CpuFeatures::IsSupported(AVX)) {
     CpuFeatureScope scope(this, AVX);
-    vxorpd(dst, dst, dst);
     vcvtlsi2sd(dst, dst, src);
   } else {
-    xorpd(dst, dst);
     cvtlsi2sd(dst, src);
   }
 }
@@ -802,10 +798,8 @@ void TurboAssembler::Cvtqsi2ss(XMMRegister dst, Operand src) {
 void TurboAssembler::Cvtqsi2sd(XMMRegister dst, Register src) {
   if (CpuFeatures::IsSupported(AVX)) {
     CpuFeatureScope scope(this, AVX);
-    vxorpd(dst, dst, dst);
     vcvtqsi2sd(dst, dst, src);
   } else {
-    xorpd(dst, dst);
     cvtqsi2sd(dst, src);
   }
 }
@@ -813,10 +807,8 @@ void TurboAssembler::Cvtqsi2sd(XMMRegister dst, Register src) {
 void TurboAssembler::Cvtqsi2sd(XMMRegister dst, Operand src) {
   if (CpuFeatures::IsSupported(AVX)) {
     CpuFeatureScope scope(this, AVX);
-    vxorpd(dst, dst, dst);
     vcvtqsi2sd(dst, dst, src);
   } else {
-    xorpd(dst, dst);
     cvtqsi2sd(dst, src);
   }
 }