[LoopPredication] Add a test demonstrating bug.

LoopPredication may introduce undefined behavior.

llvm/test/Transforms/LoopPredication/poison.ll

@@ -0,0 +1,111 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes=loop-predication < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes='require<scalar-evolution>,loop-mssa(loop-predication)' -verify-memoryssa < %s 2>&1 | FileCheck %s
+
+declare void @llvm.experimental.guard(i1, ...)
+
+; Check the case when N on latch exit might be poison.
+define i32 @test1(i32 %length, i32 %nlimit) {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[M:%.*]] = add nuw nsw i32 [[NLIMIT:%.*]], 2
+; CHECK-NEXT:    [[N:%.*]] = xor i32 [[M]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp ule i32 [[N]], [[LENGTH:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i32 0, [[LENGTH]]
+; CHECK-NEXT:    [[TMP2:%.*]] = and i1 [[TMP1]], [[TMP0]]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[OK:%.*]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[J:%.*]] = phi i32 [ [[J_NEXT:%.*]], [[OK]] ], [ 0, [[ENTRY]] ]
+; CHECK-NEXT:    [[WITHIN_BOUNDS:%.*]] = icmp ult i32 [[J]], [[LENGTH]]
+; CHECK-NEXT:    call void (i1, ...) @llvm.experimental.guard(i1 [[TMP2]], i32 9) [ "deopt"() ]
+; CHECK-NEXT:    call void @llvm.assume(i1 [[WITHIN_BOUNDS]])
+; CHECK-NEXT:    [[TMP:%.*]] = icmp ult i32 [[NLIMIT]], 1000
+; CHECK-NEXT:    br i1 [[TMP]], label [[OK]], label [[EXIT:%.*]]
+; CHECK:       ok:
+; CHECK-NEXT:    [[I_NEXT]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[J_NEXT]] = add i32 [[J]], 1
+; CHECK-NEXT:    [[CONTINUE:%.*]] = icmp ult i32 [[I_NEXT]], [[N]]
+; CHECK-NEXT:    br i1 [[CONTINUE]], label [[LOOP]], label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  ; %n might be a poison.
+  %m = add nuw nsw i32 %nlimit, 2
+  %n = xor i32 %m, 1
+  br label %loop
+
+loop:
+  %i = phi i32 [ %i.next, %ok ], [ 0, %entry ]
+  %j = phi i32 [ %j.next, %ok ], [ 0, %entry ]
+  %within.bounds = icmp ult i32 %j, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  ; This check guarantees %n is not a posion.
+  %tmp = icmp ult i32 %nlimit, 1000
+  br i1 %tmp, label %ok, label %exit
+
+ok:
+  %i.next = add i32 %i, 1
+  %j.next = add i32 %j, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  ret i32 0
+}
+
+
+; Check the case when start value of IV might be a poison.
+define i32 @test2(i32 noundef %length, i32 noundef %nlimit, i32 %istart) {
+; CHECK-LABEL: @test2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[M:%.*]] = add nuw nsw i32 [[ISTART:%.*]], 2
+; CHECK-NEXT:    [[ISTART2:%.*]] = xor i32 [[M]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[ISTART2]], [[LENGTH:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[TMP0]], -1
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ule i32 [[NLIMIT:%.*]], [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ult i32 1, [[LENGTH]]
+; CHECK-NEXT:    [[TMP4:%.*]] = and i1 [[TMP3]], [[TMP2]]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[OK:%.*]] ], [ [[ISTART2]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[J:%.*]] = phi i32 [ [[J_NEXT:%.*]], [[OK]] ], [ 1, [[ENTRY]] ]
+; CHECK-NEXT:    [[WITHIN_BOUNDS:%.*]] = icmp ult i32 [[J]], [[LENGTH]]
+; CHECK-NEXT:    call void (i1, ...) @llvm.experimental.guard(i1 [[TMP4]], i32 9) [ "deopt"() ]
+; CHECK-NEXT:    call void @llvm.assume(i1 [[WITHIN_BOUNDS]])
+; CHECK-NEXT:    [[TMP:%.*]] = icmp ult i32 [[ISTART]], 1000
+; CHECK-NEXT:    br i1 [[TMP]], label [[OK]], label [[EXIT:%.*]]
+; CHECK:       ok:
+; CHECK-NEXT:    [[I_NEXT]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[J_NEXT]] = add i32 [[J]], 1
+; CHECK-NEXT:    [[CONTINUE:%.*]] = icmp ult i32 [[I_NEXT]], [[NLIMIT]]
+; CHECK-NEXT:    br i1 [[CONTINUE]], label [[LOOP]], label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  ; %m might be a poison.
+  %m = add nuw nsw i32 %istart, 2
+  %istart2 = xor i32 %m, 1
+  br label %loop
+
+loop:
+  %i = phi i32 [ %i.next, %ok ], [ %istart2, %entry ]
+  %j = phi i32 [ %j.next, %ok ], [ 1, %entry ]
+  %within.bounds = icmp ult i32 %j, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+  ; This check guarantees %n is not a posion.
+  %tmp = icmp ult i32 %istart, 1000
+  br i1 %tmp, label %ok, label %exit
+
+ok:
+  %i.next = add i32 %i, 1
+  %j.next = add i32 %j, 1
+  %continue = icmp ult i32 %i.next, %nlimit
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  ret i32 0
+}