[AArch64] Avoid materializing constant 1 when generating cneg instructions.

Instead of

 cmp w0, #1
 orr w8, wzr, #0x1
 cneg w0, w8, ne

we now generate

 cmp w0, #1
 csinv w0, w0, wzr, eq

PR28965

llvm-svn: 285217

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AArch64/cond-sel-value-prop.ll b/llvm/test/CodeGen/AArch64/cond-sel-value-prop.ll
index cc0aad1a0bf..0c8b5e559a3 100644
--- a/llvm/test/CodeGen/AArch64/cond-sel-value-prop.ll
+++ b/llvm/test/CodeGen/AArch64/cond-sel-value-prop.ll
@@ -97,3 +97,14 @@ define i64 @test9(i64 %x) {
   %res = select i1 %cmp, i64 7, i64 -1
   ret i64 %res
 }
+
+; Rather than use a CNEG, use a CSINV to transform "a == 1 ? 1 : -1" to
+; "a == 1 ? a : -1" to avoid materializing a constant.
+; CHECK-LABEL: test10:
+; CHECK: cmp w[[REG:[0-9]]], #1
+; CHECK: cneg w0, w[[REG]], ne
+define i32 @test10(i32 %x) {
+  %cmp = icmp eq i32 %x, 1
+  %res = select i1 %cmp, i32 1, i32 -1
+  ret i32 %res
+}