[IR] Fix string overlap issue in Value::setNameImpl

[w-gc]

No description provided.

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[llvmbot]

@llvm/pr-subscribers-llvm-ir

Author: None (w-gc)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/158288.diff

1 Files Affected:

• (modified) llvm/lib/IR/Value.cpp (+9)

diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index 4e8f359481b81..a7aa7fb04d99e 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -374,6 +374,15 @@ void Value::setNameImpl(const Twine &NewName) {
   // NOTE: Could optimize for the case the name is shrinking to not deallocate
   // then reallocated.
   if (hasName()) {
+    if (!NameRef.empty()) {
+      StringRef OldNameRef = getName();
+      if ((OldNameRef.bytes_begin() < NameRef.bytes_end()) &&
+          (NameRef.bytes_begin() < OldNameRef.bytes_end())) {
+        NewName.toVector(NameData);
+        NameRef = StringRef(NameData.data(), NameData.size());
+      }
+    }
+
     // Remove old name.
     ST->removeValueName(getValueName());
     destroyValueName();

[zhaosiying12138]

LGTM.

[nikic]

Can you please add a unit test for this?

[nikic]

Suggested change

	// Copy NewName forcely if the memory overlaps.
	// Copy NewName if the memory overlaps.

or "forcefully", but I think you can just omit it.

[nikic]

I believe this is technically UB in the case where it doesn't overlap. One has to use std::less in this case.