[PATCH] D97160: [DAGCombiner] Optimize SMULO/UMULO if we can prove that overflow is impossible.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:4672
+      bool Overflow;
+      (void)N0Known.getMaxValue().umul_ov(N1Known.getMaxValue(), Overflow);
+      if (!Overflow)
----------------
RKSimon wrote:
> Is it worth moving this to something like:
> ```
> KnownBits KnownBits::umul_ov(const KnownBits &LHS,const KnownBits &RHS,llvm:Optional<bool> &Overflow)
> ```
Are you suggesting to merge this with computeForMul? Just calling APInt::umul_ov doesn't give you the right known bits for the data result. So we would need the logic from computeForMul.


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  https://reviews.llvm.org/D97160/new/

https://reviews.llvm.org/D97160