[llvm] [LegalizeDAG] Optimize CodeGen for `ISD::CTLZ_ZERO_UNDEF` (PR #83039)

[Manish Kausik H via llvm-commits]

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@@ -0,0 +1,18 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc < %s --mtriple=aarch64 | FileCheck %s
+
+declare i8 @llvm.ctlz.i8(i8, i1 immarg)
+
+define i32 @clz_nzu8(ptr %num) {
+; CHECK-LABEL: clz_nzu8:
+; CHECK:       // %bb.0: // %start
+; CHECK-NEXT:    ldrb w8, [x0]
+; CHECK-NEXT:    lsl w8, w8, #24
+; CHECK-NEXT:    clz w0, w8
+; CHECK-NEXT:    ret
+start:
+  %self = load i8, ptr %num, align 1
+  %0 = call i8 @llvm.ctlz.i8(i8 %self, i1 true)
+  %_0 = zext i8 %0 to i32
+  ret i32 %_0
+}
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Nirhar wrote:

Added!

https://github.com/llvm/llvm-project/pull/83039