[clang] [Serialization] Use StringRef::substr (NFC) (PR #139678)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-modules

Author: Kazu Hirata (kazutakahirata)

<details>
<summary>Changes</summary>

StringRef::substr is shorter here because we can rely on its default
second parameter.


---
Full diff: https://github.com/llvm/llvm-project/pull/139678.diff


1 Files Affected:

- (modified) clang/lib/Serialization/ASTWriter.cpp (+1-1) 


``````````diff
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index c4c0603839c62..7de510c85bfed 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -1237,7 +1237,7 @@ ASTWriter::createSignature() const {
   Hasher.update(
       AllBytes.slice(UnhashedControlBlockRange.second, ASTBlockRange.first));
   //  3. After the AST block.
-  Hasher.update(AllBytes.slice(ASTBlockRange.second, StringRef::npos));
+  Hasher.update(AllBytes.substr(ASTBlockRange.second));
   ASTFileSignature Signature = ASTFileSignature::create(Hasher.result());
 
   return std::make_pair(ASTBlockHash, Signature);

``````````

</details>


https://github.com/llvm/llvm-project/pull/139678