[PATCH] D87034: [KnownBits] Implement accurate unsigned and signed max and min

[Jay Foad via Phabricator via llvm-commits]

foad added inline comments.


================
Comment at: llvm/lib/Support/KnownBits.cpp:113
+  LHSgeRHS.setLowBits(BitWidth - LHSgtRHS.countLeadingZeros());
+  if (LHSgeRHS.isAllOnesValue()) {
+    Res.Zero |= LHS.Zero;
----------------
nikic wrote:
> nikic wrote:
> > How does this differ from `LHS.getMinValue().uge(RHS.getMaxValue())`?
> Generally I think this code should be structured something like this:
> 
> ```
>   if (LHS.getMinValue().uge(RHS.getMaxValue()))
>     return LHS;
>   if (RHS.getMinValue().uge(LHS.getMaxValue()))
>     return RHS;
> 
>   // If the result of the umax is LHS then it must be greater than or equal to
>   // the minimum possible value of RHS. Likewise for RHS. Any known bits that
>   // are common to these two values are also known in the result.
>   KnownBits L = LHS.makeGE(RHS.getMinValue());
>   KnownBits R = RHS.makeGE(LHS.getMinValue());
>   return KnownBits(L.Zero & R.Zero, L.One & R.One);
> ```
Thanks! Can you simplify `makeGE` for me too? :)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D87034/new/

https://reviews.llvm.org/D87034