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

[Nikita Popov via llvm-commits]

================
@@ -1661,6 +1698,16 @@ 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))
+    if (Value *FoldedCttz =
+            foldMinimumOverTrailingOrLeadingZeroCount<Intrinsic::cttz>(
+                I0, I1, DL, Builder))
+      return replaceInstUsesWith(*II, FoldedCttz);
+    // umin(ctlz(x), const) --> ctlz(x | ((SignedMin >> const)))
----------------
nikic wrote:

```suggestion
    // umin(ctlz(x), const) --> ctlz(x | (SignedMin >> const))
```

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