[PATCH] D123453: [InstCombine] Fold mul nuw+lshr exact to a single multiplication when the latter is a factor

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp:1177
+      // lshr exact (mul nuw x, (c << ShAmtC)), ShAmtC -> mul nuw x, c
+      if (Op0->hasOneUse() && I.isExact()) {
+        APInt NewMulC = MulC->lshr(ShAmtC);
----------------
1. No one-use check needed, only a single instruction is produced.
2. I believe, while that `lshr` is obviously `exact`, your own proof shows that there is no need to check that it is marked as such?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D123453/new/

https://reviews.llvm.org/D123453