[llvm] [ARM] Custom lower abdu and abds (PR #182696)

[Eli Friedman via llvm-commits]

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@@ -953,9 +946,10 @@ define i8 @abd_subnsw_i8(i8 %a, i8 %b) nounwind {
 ; CHECK-ARM-LABEL: abd_subnsw_i8:
 ; CHECK-ARM:       @ %bb.0:
 ; CHECK-ARM-NEXT:    sub r0, r0, r1
+; CHECK-ARM-NEXT:    mov r2, #0
 ; CHECK-ARM-NEXT:    lsl r1, r0, #24
-; CHECK-ARM-NEXT:    eor r0, r0, r1, asr #31
-; CHECK-ARM-NEXT:    sub r0, r0, r1, asr #31
+; CHECK-ARM-NEXT:    asrs r0, r1, #24
+; CHECK-ARM-NEXT:    submi r0, r2, r1, asr #24
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efriedma-quic wrote:

abd_subnsw_i8 is a regression.

https://github.com/llvm/llvm-project/pull/182696