[llvm] [InstCombine] Pattern match minmax calls for unsigned saturation. (PR #99250)

[Yingwei Zheng via llvm-commits]

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@@ -1117,68 +1117,92 @@ static Instruction *moveAddAfterMinMax(IntrinsicInst *II,
   return IsSigned ? BinaryOperator::CreateNSWAdd(NewMinMax, Add->getOperand(1))
                   : BinaryOperator::CreateNUWAdd(NewMinMax, Add->getOperand(1));
 }
-/// Match a sadd_sat or ssub_sat which is using min/max to clamp the value.
-Instruction *InstCombinerImpl::matchSAddSubSat(IntrinsicInst &MinMax1) {
+/// Match a [s|u]add_sat or [s|u]sub_sat which is using min/max to clamp the
+/// value.
+Instruction *InstCombinerImpl::matchAddSubSat(IntrinsicInst &MinMax1) {
   Type *Ty = MinMax1.getType();
 
-  // We are looking for a tree of:
-  // max(INT_MIN, min(INT_MAX, add(sext(A), sext(B))))
-  // Where the min and max could be reversed
-  Instruction *MinMax2;
+  // 1. We are looking for a tree of signed saturation:
+  //    smax(SINT_MIN, smin(SINT_MAX, add|sub(sext(A), sext(B))))
+  //    Where the smin and smax could be reversed.
+  // 2. A tree of unsigned saturation:
+  //    smax(UINT_MIN, smin(UINT_MAX, sub(zext(A), zext(B))))
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dtcxzyw wrote:

`UINT_MAX` is -1. It looks incorrect.


https://github.com/llvm/llvm-project/pull/99250