[PATCH] D128364: [InstCombine] Look through more casts when folding memchr and memcmp

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:4194
+  const GlobalVariable *GV;
   if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
+    // Drill down into the first operand, ignoring any intervening casts,
----------------
You can move this out of the `GEPOperator` block and also drop the stripPointerCasts() above (and the repeated checks of GV below it). All cases can be treated uniformly.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:4239
+    // library calls to safer expressions.  This is preferable to making
+    // the calls although it prevents sanitizers from detecting such calls.
+    Slice.Length = Length < Offset ? 0 : Length - Offset;
----------------
I wouldn't claim that folding these is really "safer", it's just a (UB-based) optimization.


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  https://reviews.llvm.org/D128364/new/

https://reviews.llvm.org/D128364