[llvm] [InstCombine] Fold Minimum over Trailing/Leading Bits Counts (PR #90402)

[via llvm-commits]

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@@ -1633,6 +1667,21 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       Value *Cmp = Builder.CreateICmpNE(I0, Zero);
       return CastInst::Create(Instruction::ZExt, Cmp, II->getType());
     }
+    // umin(cttz(x), const) --> cttz(x | (1 << const))
+    Value *X;
+    Constant *Y;
+    Value *Z;
+    if (match(I0, m_OneUse(m_Cttz(m_Value(X), m_Value(Z)))) &&
+        match(I1, m_Constant(Y))) {
+      return foldMinimumOverTrailingOrLeadingZeroCount<Intrinsic::cttz>(
+          II, X, Z, Y, DL, Builder);
+    }
+    // umin(ctlz(x), const) --> ctlz(x | ((1 << (bitwidth - 1) >> const)))
+    if (match(I0, m_OneUse(m_Ctlz(m_Value(X), m_Value(Z)))) &&
+        match(I1, m_Constant(Y))) {
+      return foldMinimumOverTrailingOrLeadingZeroCount<Intrinsic::ctlz>(
+          II, X, Z, Y, DL, Builder);
+    }
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goldsteinn wrote:

The matching code could also be in `foldMinimumOverTrailing...`. Just pass the intrinsic ID in question and use `m_Intrinsic`

https://github.com/llvm/llvm-project/pull/90402