[clang] Update Clang.cpp (PR #77031)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: hw-1 (hw-1)

<details>
<summary>Changes</summary>

fix bug with PCH check failed, detail with https://github.com/llvm/llvm-project/issues/76923

---
Full diff: https://github.com/llvm/llvm-project/pull/77031.diff


1 Files Affected:

- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+1-1) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 2d8ef841d4f6be..bb8b496dbfe5fc 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -951,7 +951,7 @@ static void handleAMDGPUCodeObjectVersionOptions(const Driver &D,
 static bool hasClangPchSignature(const Driver &D, StringRef Path) {
   if (llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MemBuf =
           D.getVFS().getBufferForFile(Path))
-    return (*MemBuf)->getBuffer().starts_with("CPCH");
+    return (*MemBuf)->getBuffer().substr(0x500,-1).starts_with("CPCH");
   return false;
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/77031