Fix SCEV forgetMemoizedResults should search and destroy backedge exprs.

Fixes PR15570: SEGV: SCEV back-edge info invalid after dead code removal.

Indvars creates a SCEV expression for the loop's back edge taken
count, then determines that the comparison is always true and
removes it.

When loop-unroll asks for the expression, it contains a NULL
SCEVUnknkown (as a CallbackVH).

forgetMemoizedResults should invalidate the loop back edges expression.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177986 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 0 deletions

diff --git a/test/Analysis/ScalarEvolution/scev-invalid.ll b/test/Analysis/ScalarEvolution/scev-invalid.ll
new file mode 100644
index 0000000000..aac0d319ae
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/scev-invalid.ll
@@ -0,0 +1,34 @@
+; RUN: opt < %s -S -indvars -loop-unroll | FileCheck %s
+;
+; PR15570: SEGV: SCEV back-edge info invalid after dead code removal.
+;
+; Indvars creates a SCEV expression for the loop's back edge taken
+; count, then determines that the comparison is always true and
+; removes it.
+;
+; When loop-unroll asks for the expression, it contains a NULL
+; SCEVUnknkown (as a CallbackVH).
+;
+; forgetMemoizedResults should invalidate the backedge taken count expression.
+
+; CHECK: @test
+; CHECK-NOT: phi
+; CHECK-NOT: icmp
+; CHECK: ret void
+define void @test() {
+entry:
+  %xor1 = xor i32 0, 1
+  br label %b17
+
+b17:
+  br i1 undef, label %b22, label %b18
+
+b18:
+  %phi1 = phi i32 [ %add1, %b18 ], [ %xor1, %b17 ]
+  %add1 = add nsw i32 %phi1, -1
+  %cmp1 = icmp sgt i32 %add1, 0
+  br i1 %cmp1, label %b18, label %b22
+
+b22:
+  ret void
+}