[PATCH] D154725: [SimplifyLibCalls] Fold strcmp for short string literals

[Nikita Popov via Phabricator via llvm-commits]

nikic requested changes to this revision.
nikic added inline comments.
This revision now requires changes to proceed.


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Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:576
+    if (Str2.size() == 1) {
+      return FirstCharacterSub;
+    }
----------------
This will return an incorrect result if the first character of Str1 and Str2 is the same, but Str1 has length greater than one.


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Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:581
+        B.CreateLoad(B.getInt8Ty(),
+                     B.CreateConstInBoundsGEP1_32(B.getInt8Ty(), Str1P, 1)),
+        B.getInt32Ty(), true);
----------------
This may perform an out of bounds access for zero-length strings.


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Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:612
   if (!HasStr1 && HasStr2) {
     if (canTransformToMemCmp(CI, Str1P, Len2, DL))
       return copyFlags(
----------------
This is the transform that implements what you're trying to do, but taking dereferenceability into account.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D154725/new/

https://reviews.llvm.org/D154725