================
@@ -897,7 +897,20 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst
&Trunc) {
}
}
- return nullptr;
+ bool Changed = false;
+ if (!Trunc.hasNoSignedWrap() &&
+ ComputeMaxSignificantBits(Src, /*Depth=*/0, &Trunc) <= DestWidth) {
+ Trunc.setHasNoSignedWrap(true);
+ Changed = true;
+ }
+ if (!Trunc.hasNoUnsignedWrap() &&
+ MaskedValueIsZero(Src, APInt::getBitsSetFrom(SrcWidth, DestWidth),
+ /*Depth=*/0, &Trunc)) {
+ Trunc.setHasNoUnsignedWrap(true);
+ Changed = true;
----------------
dtcxzyw wrote:
> We can't infer nsw, but we can infer nuw.
I prefer to infer both flags here, then we may reuse KnownBits in further
patches.
> Do you see any reason why doing this in SimplifyDemanded would be problematic?
`SimplifyDemanded` is context-sensitive. IMO it is not the right place to infer
flags.
https://github.com/llvm/llvm-project/pull/87910
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