[llvm] [InstCombine] Fold max(max(x, c1) << c2, c3) —> max(x << c2, c3) when c3 >= c1 * 2 ^ c2 (PR #140526)

[Yingwei Zheng via llvm-commits]

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@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i8 @src(i8 %arg0) {
+; CHECK-LABEL: @src(
+; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw i8 [[ARG0:%.*]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = call i8 @llvm.umax.i8(i8 [[TMP1]], i8 16)
+; CHECK-NEXT:    ret i8 [[TMP2]]
+;
+  %1 = call i8 @llvm.umax.i8(i8 %arg0, i8 1)
+  %2 = shl nuw i8 %1, 1
+  %3 = call i8 @llvm.umax.i8(i8 %2, i8 16)
+  ret i8 %3
+}
+
+define i8 @tgt(i8 %arg0) {
+; CHECK-LABEL: @tgt(
+; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw i8 [[ARG0:%.*]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = call i8 @llvm.umax.i8(i8 [[TMP1]], i8 16)
+; CHECK-NEXT:    ret i8 [[TMP2]]
+;
+  %1 = shl nuw i8 %arg0, 1
+  %2 = call i8 @llvm.umax.i8(i8 %1, i8 16)
+  ret i8 %2
+}
+
+declare i8 @llvm.umax.i8(i8, i8)
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dtcxzyw wrote:

```suggestion
```
Intrinsic declarations are unnecessary.


https://github.com/llvm/llvm-project/pull/140526