[llvm] [InstSimplify] Simplify the select with integer comparison relationship (PR #66668)

[via llvm-commits]

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@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
+
+; https://alive2.llvm.org/ce/z/zKX64J
+define i32 @pr54735(i32 noundef %x, i32 noundef %y) {
+; CHECK-LABEL: @pr54735(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[COND_TRUE:%.*]], label [[COND_END:%.*]]
+; CHECK:       cond.true:
+; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i32 [[X]], [[Y]]
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[SUB]], 1
+; CHECK-NEXT:    br label [[COND_END]]
+; CHECK:       cond.end:
+; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[ADD]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    ret i32 [[COND]]
+;
+entry:
+  %cmp = icmp sgt i32 %x, %y
+  br i1 %cmp, label %cond.true, label %cond.end
+
+cond.true:                                        ; preds = %entry
+  %sub = sub nsw i32 %x, %y
+  %add = add nsw i32 %sub, 1
+  %neg = xor i32 %sub, -1                         ; sub nsw i32 0, %add
+  %abscond = icmp slt i32 %sub, -1
+  %abs = select i1 %abscond, i32 %neg, i32 %add
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i32 [ %abs, %cond.true ], [ 0, %entry ]
+  ret i32 %cond
+}
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goldsteinn wrote:

Please split to two commits, 1st is tests before the change, 2nd is change (with updated tests). Allows us to see the actual affects of the patch.

https://github.com/llvm/llvm-project/pull/66668