[Test] NFC. Add a test exposing a SCEV bug causing an LSR miscompile

llvm/test/Transforms/LoopStrengthReduce/scev-incorrect-nuw-inference.ll

@@ -0,0 +1,69 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt < %s -loop-reduce -S | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128-ni:1-p2:32:8:8:32-ni:2"
+target triple = "x86_64-unknown-linux-gnu"
+
+; FIXME: the returned value should be equal to
+;     zext (trunk (%phi-1) to i16) to i64
+;   or simply
+;     zext (%phi-1) to i64
+; which means it should be equal to 1209. Currently, due to a bug in SCEV, it's
+; over 65534.
+define noundef i64 @test() {
+; CHECK-LABEL: define noundef i64 @test() {
+; CHECK-NEXT:  bb2:
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[LSR_IV:%.*]] = phi i64 [ [[LSR_IV_NEXT:%.*]], [[BB10:%.*]] ], [ 0, [[BB2:%.*]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[LSR_IV]], 65535
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[LSR_IV]], 65407
+; CHECK-NEXT:    [[ICMP5:%.*]] = icmp ult i64 [[TMP1]], -256
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[TMP0]] to i32
+; CHECK-NEXT:    [[ICMP6:%.*]] = icmp ult i32 [[TMP2]], 128
+; CHECK-NEXT:    [[OR:%.*]] = or i1 [[ICMP5]], [[ICMP6]]
+; CHECK-NEXT:    br i1 [[OR]], label [[BB10]], label [[BB7:%.*]]
+; CHECK:       bb7:
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[LSR_IV]] to i32
+; CHECK-NEXT:    call void @foo(i32 [[TMP1]])
+; CHECK-NEXT:    unreachable
+; CHECK:       bb10:
+; CHECK-NEXT:    [[LSR_IV_NEXT]] = add nuw nsw i64 [[LSR_IV]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = add i64 [[LSR_IV_NEXT]], -1
+; CHECK-NEXT:    [[TMP:%.*]] = trunc i64 [[TMP2]] to i32
+; CHECK-NEXT:    [[ICMP12:%.*]] = icmp ult i32 [[TMP]], 1210
+; CHECK-NEXT:    br i1 [[ICMP12]], label [[BB3]], label [[BB13:%.*]]
+; CHECK:       bb13:
+; CHECK-NEXT:    [[TMP3:%.*]] = add i64 [[LSR_IV_NEXT]], 65534
+; CHECK-NEXT:    ret i64 [[TMP3]]
+;
+bb2:
+  br label %bb3
+
+bb3:                                              ; preds = %bb10, %bb2
+  %phi = phi i32 [ 0, %bb2 ], [ %add11, %bb10 ]
+  %add = add nuw nsw i32 %phi, 65535
+  %and = and i32 %add, 65535
+  %zext = zext i32 %and to i64
+  %add4 = add nsw i64 %zext, -128
+  %icmp5 = icmp ult i64 %add4, -256
+  %icmp6 = icmp ult i32 %and, 128
+  %or = or i1 %icmp5, %icmp6
+  br i1 %or, label %bb10, label %bb7
+
+bb7:                                              ; preds = %bb3
+  call void @foo(i32 %phi)
+  unreachable
+
+bb10:                                             ; preds = %bb3
+  %add11 = add nuw nsw i32 %phi, 1
+  %icmp12 = icmp ult i32 %phi, 1210
+  br i1 %icmp12, label %bb3, label %bb13
+
+bb13:                                             ; preds = %bb10
+  ret i64 %zext
+
+  uselistorder i32 %phi, { 0, 3, 1, 2 }
+}
+
+declare void @foo(i32)