================
@@ -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;
+ }
----------------
goldsteinn wrote:
>From an efficiency POV, I think you should probably startout with a
>`computeKnownBits` on src and see if you get lucky about leading ones / zeros.
>Then if you don't, do a call to `computeMaxSignificantBits`.
https://github.com/llvm/llvm-project/pull/87910
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