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

[Huihui Zhang via llvm-commits]

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@@ -1117,68 +1117,108 @@ 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, sub(zext(A), zext(B)))
+  //    Or umin(UINT_MAX, add(zext(A), zext(B))).
+  Instruction *MinMax2 = nullptr;
   BinaryOperator *AddSub;
-  const APInt *MinValue, *MaxValue;
-  if (match(&MinMax1, m_SMin(m_Instruction(MinMax2), m_APInt(MaxValue)))) {
-    if (!match(MinMax2, m_SMax(m_BinOp(AddSub), m_APInt(MinValue))))
+  const APInt *MinValue = nullptr, *MaxValue = nullptr;
+  bool IsUnsignedSaturate = false;
+  // Pattern match for unsigned saturation.
+  if (match(&MinMax1, m_UMin(m_BinOp(AddSub), m_APInt(MaxValue)))) {
+    // Bail out if AddSub could be negative.
+    if (!isKnownNonNegative(AddSub, SQ.getWithInstruction(AddSub)))
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huihzhang wrote:

This check was used to reject "umin(UINT_MAX, sub) -> usub_sat". 
I pushed a new update to check for BinOp opcode 'Add', so that !isKnownNonNegative check can be deleted.

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