[ValueTracking] avoid crashing from bad assumptions (PR31809)
A program may contain llvm.assume info that disagrees with other analysis.
This may be caused by UB in the program, so we must not crash because of that.
As noted in the code comments:
https://llvm.org/bugs/show_bug.cgi?id=31809
...we can do better, but this at least avoids the assert/crash in the bug report.
Differential Revision: https://reviews.llvm.org/D29395
llvm-svn: 293773
diff --git a/llvm/test/Transforms/InstSimplify/assume.ll b/llvm/test/Transforms/InstSimplify/assume.ll
index 2487a9c..2edcc0c 100644
--- a/llvm/test/Transforms/InstSimplify/assume.ll
+++ b/llvm/test/Transforms/InstSimplify/assume.ll
@@ -10,5 +10,41 @@
}
+; The alloca guarantees that the low bits of %a are zero because of alignment.
+; The assume says the opposite. The assume is processed last, so that's the
+; return value. There's no way to win (we can't undo transforms that happened
+; based on half-truths), so just don't crash.
+
+define i64 @PR31809() {
+; CHECK-LABEL: @PR31809(
+; CHECK-NEXT: ret i64 3
+;
+ %a = alloca i32
+ %t1 = ptrtoint i32* %a to i64
+ %cond = icmp eq i64 %t1, 3
+ call void @llvm.assume(i1 %cond)
+ ret i64 %t1
+}
+
+; Similar to above: there's no way to know which assumption is truthful,
+; so just don't crash. The second icmp+assume gets processed later, so that
+; determines the return value. This can be improved by permanently invalidating
+; the cached assumptions for this function.
+
+define i8 @conflicting_assumptions(i8 %x) {
+; CHECK-LABEL: @conflicting_assumptions(
+; CHECK-NEXT: call void @llvm.assume(i1 false)
+; CHECK-NEXT: [[COND2:%.*]] = icmp eq i8 %x, 4
+; CHECK-NEXT: call void @llvm.assume(i1 [[COND2]])
+; CHECK-NEXT: ret i8 5
+;
+ %add = add i8 %x, 1
+ %cond1 = icmp eq i8 %x, 3
+ call void @llvm.assume(i1 %cond1)
+ %cond2 = icmp eq i8 %x, 4
+ call void @llvm.assume(i1 %cond2)
+ ret i8 %add
+}
+
declare void @llvm.assume(i1) nounwind