[PATCH] D148609: [InstCombine] Fix buggy `(mul X, Y)` -> `(shl X, Log2(Y))` transform PR62175

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp:189
 static Value *takeLog2(IRBuilderBase &Builder, Value *Op, unsigned Depth,
-                       bool DoFold);
+                       bool RequireNoOverflow, bool DoFold);
 
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Replace RequireNoOverflow with an AssumeNonZero flag. This is what justifies it for division.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp:1227
+      if (!Usable && match(X, m_SpecificInt(1)))
+        Usable = true;
+    }
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Don't we always infer nuw for shl of one?


Repository:
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  https://reviews.llvm.org/D148609/new/

https://reviews.llvm.org/D148609