[clang] Revert "[Clang] [Lexer] Detect SSE4.2 availability at runtime in fastParseASCIIIdentifier" (PR #174946)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Thibault Monnier (Thibault-Monnier)

<details>
<summary>Changes</summary>

Reverts llvm/llvm-project#<!-- -->171914 because of compilation failures reported.

---
Full diff: https://github.com/llvm/llvm-project/pull/174946.diff


1 Files Affected:

- (modified) clang/lib/Lex/Lexer.cpp (+10-30) 


``````````diff
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index 5e8ed5f815c7b..afebef0974016 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -36,7 +36,6 @@
 #include "llvm/Support/NativeFormatting.h"
 #include "llvm/Support/Unicode.h"
 #include "llvm/Support/UnicodeCharRanges.h"
-
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
@@ -46,7 +45,7 @@
 #include <optional>
 #include <string>
 
-#if defined(__i386__) || defined(__x86_64__)
+#ifdef __SSE4_2__
 #include <nmmintrin.h>
 #endif
 
@@ -1920,21 +1919,10 @@ bool Lexer::LexUnicodeIdentifierStart(Token &Result, uint32_t C,
   return true;
 }
 
-static const char *fastParseASCIIIdentifierScalar(const char *CurPtr) {
-  unsigned char C = *CurPtr;
-  while (isAsciiIdentifierContinue(C))
-    C = *++CurPtr;
-  return CurPtr;
-}
-
-// Fast path for lexing ASCII identifiers using SSE4.2 instructions.
-// Only enabled on x86/x86_64 when building with a compiler that supports
-// the 'target' attribute, which is used for runtime dispatch. Otherwise, we
-// fall back to the scalar implementation.
-#if (defined(__i386__) || defined(__x86_64__)) && defined(__has_attribute) &&  \
-    __has_attribute(target) && !defined(_MSC_VER)
-__attribute__((target("sse4.2"))) static const char *
-fastParseASCIIIdentifierSSE42(const char *CurPtr, const char *BufferEnd) {
+static const char *
+fastParseASCIIIdentifier(const char *CurPtr,
+                         [[maybe_unused]] const char *BufferEnd) {
+#ifdef __SSE4_2__
   alignas(16) static constexpr char AsciiIdentifierRange[16] = {
       '_', '_', 'A', 'Z', 'a', 'z', '0', '9',
   };
@@ -1954,20 +1942,12 @@ fastParseASCIIIdentifierSSE42(const char *CurPtr, const char *BufferEnd) {
       continue;
     return CurPtr;
   }
-
-  return fastParseASCIIIdentifierScalar(CurPtr);
-}
-
-__attribute__((target("sse4.2"))) static const char *
-fastParseASCIIIdentifier(const char *CurPtr, const char *BufferEnd) {
-  return fastParseASCIIIdentifierSSE42(CurPtr, BufferEnd);
-}
-
-__attribute__((target("default")))
 #endif
-static const char *fastParseASCIIIdentifier(const char *CurPtr,
-                                            const char *BufferEnd) {
-  return fastParseASCIIIdentifierScalar(CurPtr);
+
+  unsigned char C = *CurPtr;
+  while (isAsciiIdentifierContinue(C))
+    C = *++CurPtr;
+  return CurPtr;
 }
 
 bool Lexer::LexIdentifierContinue(Token &Result, const char *CurPtr) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/174946