[PhaseOrdering] Add PR45687 test coverage

This is a mixture of instcombine/simplfycfg/instcombine to recognise and then remove the abs pattern

diff --git a/llvm/test/Transforms/PhaseOrdering/pr45687.ll b/llvm/test/Transforms/PhaseOrdering/pr45687.ll
new file mode 100644 (file)
index 0000000..494255d
--- /dev/null
+++ b/llvm/test/Transforms/PhaseOrdering/pr45687.ll
@@ -0,0 +1,29 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -O2 -S < %s -enable-new-pm=0 | FileCheck %s
+; RUN: opt -passes='default<O2>' -S < %s | FileCheck %s
+
+define void @PR45687(i32 %0)  {
+; CHECK-LABEL: @PR45687(
+; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[TMP0:%.*]], 1
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ult i32 [[TMP2]], 3
+; CHECK-NEXT:    tail call void @llvm.assume(i1 [[TMP3]])
+; CHECK-NEXT:    ret void
+;
+  %2 = add i32 %0, 1
+  %3 = icmp ult i32 %2, 3
+  tail call void @llvm.assume(i1 %3)
+  %4 = icmp slt i32 %0, 0
+  %5 = sub nsw i32 0, %0
+  %6 = select i1 %4, i32 %5, i32 %0
+  %7 = icmp sgt i32 %6, 1
+  br i1 %7, label %8, label %9
+8:
+  tail call void @g()
+  br label %9
+9:
+  ret void
+}
+
+declare void @llvm.assume(i1)
+
+declare void @g()