[llvm] Lowering `~x | (x - 1)` to `~blsi(x)` (PR #186722)

[via llvm-commits]

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@@ -0,0 +1,14 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=+bmi -filetype=asm | FileCheck %s
+
+define i64 @foo(i64 %x) {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    blsiq %rdi, %rax
+; CHECK-NEXT:    notq %rax
+; CHECK-NEXT:    retq
+  %neg = sub i64 0, %x
+  %and = and i64 %x, %neg
+  %not = xor i64 %and, -1
+  ret i64 %not
+}
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user1342234 wrote:

Done, thanks

https://github.com/llvm/llvm-project/pull/186722