[llvm] [InstCombine] Don't use dominating conditions to transform sub into xor. (PR #88566)

[via llvm-commits]

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@@ -0,0 +1,54 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -passes="default<O3>" -mcpu=skx -S | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @foo(ptr noalias noundef %0, ptr noalias noundef %1) optsize {
+; CHECK-LABEL: define void @foo(
+; CHECK-SAME: ptr noalias nocapture noundef readonly [[TMP0:%.*]], ptr noalias nocapture noundef writeonly [[TMP1:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:  vector.ph:
+; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[TMP0]], i64 -28
+; CHECK-NEXT:    br label [[TMP4:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ 0, [[TMP2:%.*]] ], [ [[INDVARS_IV_NEXT:%.*]], [[TMP4]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = sub nuw nsw i64 255, [[INDVARS_IV]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[INVARIANT_GEP]], i64 [[TMP3]]
+; CHECK-NEXT:    [[WIDE_MASKED_GATHER:%.*]] = load <8 x i32>, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[TMP5:%.*]] = add nsw <8 x i32> [[WIDE_MASKED_GATHER]], <i32 5, i32 5, i32 5, i32 5, i32 5, i32 5, i32 5, i32 5>
+; CHECK-NEXT:    [[TMP6:%.*]] = shufflevector <8 x i32> [[TMP5]], <8 x i32> poison, <8 x i32> <i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0>
+; CHECK-NEXT:    [[TMP10:%.*]] = getelementptr inbounds i32, ptr [[TMP1]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    store <8 x i32> [[TMP6]], ptr [[TMP10]], align 4
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw i64 [[INDVARS_IV]], 8
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], 256
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[MIDDLE_BLOCK:%.*]], label [[TMP4]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    ret void
+;
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goldsteinn wrote:

Okay, this seems reasonably motivating for me.

https://github.com/llvm/llvm-project/pull/88566