[llvm] [InstCombine] Fold zext-add/sub-min/max-trunc to uadd.sat or usub.sat (PR #185259)

[Nikita Popov via llvm-commits]

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@@ -1086,6 +1086,28 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
 
   Value *A, *B;
   Constant *C;
+
+  // trunc(u/smin(zext(a) + zext(b), MAX)) --> uadd.sat(a, b)
+  if (match(Src,
+            m_OneUse(m_CombineOr(
+                m_UMin(m_OneUse(m_Add(m_ZExt(m_Value(A)), m_ZExt(m_Value(B)))),
+                       m_SpecificInt(APInt::getMaxValue(DestWidth))),
+                m_SMin(m_OneUse(m_Add(m_ZExt(m_Value(A)), m_ZExt(m_Value(B)))),
+                       m_SpecificInt(APInt::getMaxValue(DestWidth)))))) &&
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nikic wrote:

I'm kind of surprised this is necessary. I would have thought we have a smin->umin canonicalization for non-negative operands, but apparently we don't.

https://github.com/llvm/llvm-project/pull/185259