Better codegen for setting top bit of I64x2

Bug: v8:8460
Change-Id: I132f7332d3dda572b72404ca20297c4defb5c62b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1708450Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62815}

src/compiler/backend/x64/code-generator-x64.cc

@@ -2598,10 +2598,8 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       XMMRegister src = i.InputSimd128Register(1);
       XMMRegister tmp = i.ToSimd128Register(instr->TempAt(0));
 
-      // Sets up a mask to clear the sign bit of the 2 quadwords.
-      __ Set(kScratchRegister, 0x8000000000000000);
-      __ movq(kScratchDoubleReg, kScratchRegister);
-      __ pshufd(kScratchDoubleReg, kScratchDoubleReg, 0x44);
+      __ pcmpeqd(kScratchDoubleReg, kScratchDoubleReg);
+      __ psllq(kScratchDoubleReg, 63);
 
       __ movaps(tmp, src);
       __ pxor(tmp, kScratchDoubleReg);
@@ -2616,10 +2614,8 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       XMMRegister src = i.InputSimd128Register(1);
       XMMRegister tmp = i.ToSimd128Register(instr->TempAt(0));
 
-      // Sets up a mask to clear the sign bit of the 2 quadwords.
-      __ Set(kScratchRegister, 0x8000000000000000);
-      __ movq(kScratchDoubleReg, kScratchRegister);
-      __ pshufd(kScratchDoubleReg, kScratchDoubleReg, 0x44);
+      __ pcmpeqd(kScratchDoubleReg, kScratchDoubleReg);
+      __ psllq(kScratchDoubleReg, 63);
 
       __ movaps(tmp, src);
       __ pxor(dst, kScratchDoubleReg);