[clang] 8f43b84 - [ASTReader] Fix zlib header detection 0x78 after D137885

[Fangrui Song via cfe-commits]

Author: Fangrui Song
Date: 2022-11-23T13:22:44-08:00
New Revision: 8f43b84322cc255414ad996834dff09e90dc19af

URL: https://github.com/llvm/llvm-project/commit/8f43b84322cc255414ad996834dff09e90dc19af
DIFF: https://github.com/llvm/llvm-project/commit/8f43b84322cc255414ad996834dff09e90dc19af.diff

LOG: [ASTReader] Fix zlib header detection 0x78 after D137885

D137885 picked an incorrect magic so it would fail when zstd is not
enabled.

Added: 
    

Modified: 
    clang/lib/Serialization/ASTReader.cpp

Removed: 
    


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diff  --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 367fbc06a8fe..8f7cb38c6a9f 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -1452,9 +1452,10 @@ bool ASTReader::ReadSLocEntry(int ID) {
     unsigned RecCode = MaybeRecCode.get();
 
     if (RecCode == SM_SLOC_BUFFER_BLOB_COMPRESSED) {
-      // Inspect the first two bytes to 
diff erentiate zlib (\x1f\x8b) and zstd.
+      // Inspect the first byte to 
diff erentiate zlib (\x78) and zstd
+      // (little-endian 0xFD2FB528).
       const llvm::compression::Format F =
-          Blob.size() >= 2 && memcmp(Blob.data(), "\x1f\x8b", 2) == 0
+          Blob.size() > 0 && Blob.data()[0] == 0x78
               ? llvm::compression::Format::Zlib
               : llvm::compression::Format::Zstd;
       if (const char *Reason = llvm::compression::getReasonIfUnsupported(F)) {