[llvm] [InstCombine] Fold umax(nuw_mul(x, C0), x + 1) into (x == 0 ? 1 : nuw_mul(x, C0)) (PR #123468)

[Nikita Popov via llvm-commits]

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@@ -1847,6 +1847,33 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         return CastInst::Create(Instruction::ZExt, NarrowMaxMin, II->getType());
       }
     }
+    // If C0 is not 0:
+    //   umax(nuw_shl(x, C0), x + 1) -> x == 0 ? 1 : nuw_shl(x, C0)
+    // If C0 is not 0 or 1:
+    //   umax(nuw_mul(x, C0), x + 1) -> x == 0 ? 1 : nuw_mul(x, C0)
+    auto foldMaxMulShift = [&](Value *A, Value *B) -> Instruction * {
+      const APInt *C;
+      Value *X;
+      if (!(match(A, m_NUWShl(m_Value(X), m_APInt(C)))) &&
----------------
nikic wrote:

```suggestion
      if (!match(A, m_NUWShl(m_Value(X), m_APInt(C))) &&
```

https://github.com/llvm/llvm-project/pull/123468