[ia32][x64] Enable CPU feature in Assembler if supported

x64 already had logic to enable a lower CPU extension if a higher
level one was supported. Add this to ia32. And also add SSSE3->SSE3
logic.

Drive-by cleanup to remove an extra CpuFeatureScope.

Bug: v8:11154
Change-Id: I12e3aa990cc07149da213911c624468a39f4e1a3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3212811Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77291}

src/codegen/ia32/assembler-ia32.cc

@@ -324,6 +324,15 @@ Assembler::Assembler(const AssemblerOptions& options,
                      std::unique_ptr<AssemblerBuffer> buffer)
     : AssemblerBase(options, std::move(buffer)) {
   reloc_info_writer.Reposition(buffer_start_ + buffer_->size(), pc_);
+  if (CpuFeatures::IsSupported(SSE4_2)) {
+    EnableCpuFeature(SSE4_1);
+  }
+  if (CpuFeatures::IsSupported(SSE4_1)) {
+    EnableCpuFeature(SSSE3);
+  }
+  if (CpuFeatures::IsSupported(SSSE3)) {
+    EnableCpuFeature(SSE3);
+  }
 }
 
 void Assembler::GetCode(Isolate* isolate, CodeDesc* desc,

src/codegen/shared-ia32-x64/macro-assembler-shared-ia32-x64.cc

@@ -1139,7 +1139,6 @@ void SharedTurboAssembler::S128Load8Splat(XMMRegister dst, Operand src,
     vpshufb(dst, dst, scratch);
   } else {
     CpuFeatureScope ssse4_scope(this, SSE4_1);
-    CpuFeatureScope ssse3_scope(this, SSSE3);
     pinsrb(dst, src, uint8_t{0});
     xorps(scratch, scratch);
     pshufb(dst, scratch);

src/codegen/x64/assembler-x64.cc

@@ -347,6 +347,9 @@ Assembler::Assembler(const AssemblerOptions& options,
   if (CpuFeatures::IsSupported(SSE4_1)) {
     EnableCpuFeature(SSSE3);
   }
+  if (CpuFeatures::IsSupported(SSSE3)) {
+    EnableCpuFeature(SSE3);
+  }
 
 #if defined(V8_OS_WIN_X64)
   if (options.collect_win64_unwind_info) {