[Test] Add test that exposed failure on reverted patch in codegen

Author: xortator

llvm/test/CodeGen/X86/usub_inc_iv.ll

@@ -257,3 +257,55 @@ exit:
 failure:
   unreachable
 }
+
+; Here Cmp does not dominate latch.
+define i32 @test_05_neg(i32* %p, i64 %len, i32 %x, i1 %cond) {
+; CHECK-LABEL: @test_05_neg(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ], [ [[LEN:%.*]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], -1
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[IF_TRUE:%.*]], label [[BACKEDGE]]
+; CHECK:       if.true:
+; CHECK-NEXT:    [[COND_1:%.*]] = icmp eq i64 [[IV]], 0
+; CHECK-NEXT:    br i1 [[COND_1]], label [[EXIT:%.*]], label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[SUNKADDR:%.*]] = mul i64 [[IV]], 4
+; CHECK-NEXT:    [[TMP0:%.*]] = bitcast i32* [[P:%.*]] to i8*
+; CHECK-NEXT:    [[SUNKADDR1:%.*]] = getelementptr i8, i8* [[TMP0]], i64 [[SUNKADDR]]
+; CHECK-NEXT:    [[SUNKADDR2:%.*]] = getelementptr i8, i8* [[SUNKADDR1]], i64 -4
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i8* [[SUNKADDR2]] to i32*
+; CHECK-NEXT:    [[LOADED:%.*]] = load atomic i32, i32* [[TMP1]] unordered, align 4
+; CHECK-NEXT:    [[COND_2:%.*]] = icmp eq i32 [[LOADED]], [[X:%.*]]
+; CHECK-NEXT:    br i1 [[COND_2]], label [[FAILURE:%.*]], label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 -1
+; CHECK:       failure:
+; CHECK-NEXT:    unreachable
+;
+entry:
+  %scevgep = getelementptr i32, i32* %p, i64 -1
+  br label %loop
+
+loop:                                             ; preds = %backedge, %entry
+  %iv = phi i64 [ %iv.next, %backedge ], [ %len, %entry ]
+  %iv.next = add i64 %iv, -1
+  br i1 %cond, label %if.true, label %backedge
+
+if.true:
+  %cond_1 = icmp eq i64 %iv, 0
+  br i1 %cond_1, label %exit, label %backedge
+
+backedge:                                         ; preds = %loop
+  %scevgep1 = getelementptr i32, i32* %scevgep, i64 %iv
+  %loaded = load atomic i32, i32* %scevgep1 unordered, align 4
+  %cond_2 = icmp eq i32 %loaded, %x
+  br i1 %cond_2, label %failure, label %loop
+
+exit:                                             ; preds = %loop
+  ret i32 -1
+
+failure:                                          ; preds = %backedge
+  unreachable
+}