[PM/CGSCC] Teach the CGSCC pass manager components to gracefully handle

invalidated SCCs even when we do not have an updated SCC to redirect
towards.

This comes up in a fairly subtle and surprising circumstance: we need to
have a connected but internal node in the call graph which later becomes
a disconnected island, and then gets deleted. All of this needs to
happen mid-CGSCC walk. Because it is disconnected, we have no way of
computing a new "current" SCC when it gets deleted. Instead, we need to
explicitly check for a deleted "current" SCC and bail out of the current
CGSCC step. This will bubble all the way up to the post-order walk and
then resume correctly.

I've included minimal tests for this bug. The specific behavior
matches something we've seen in the wild with the new PM combined with
ThinLTO and sample PGO, but I've not yet confirmed whether this is the
only issue there.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313242 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 54 insertions, 0 deletions

diff --git a/test/Other/cgscc-disconnected-invalidation.ll b/test/Other/cgscc-disconnected-invalidation.ll
new file mode 100644
index 00000000000..0567605fcf9
--- /dev/null
+++ b/test/Other/cgscc-disconnected-invalidation.ll
@@ -0,0 +1,54 @@
+; Test that patterns of transformations which disconnect a region of the call
+; graph mid-traversal and then invalidate it function correctly.
+;
+; RUN: opt -S -passes='cgscc(inline,function(simplify-cfg))' < %s | FileCheck %s
+
+define internal void @test_scc_internal(i1 %flag) {
+; CHECK-NOT: @test_scc_internal
+entry:
+  br i1 %flag, label %then, label %else
+
+then:
+  call void @test_scc_internal(i1 false)
+  call void @test_scc_external()
+  br label %else
+
+else:
+  ret void
+}
+
+define void @test_scc_external() {
+; CHECK-LABEL: define void @test_scc_external()
+entry:
+  call void @test_scc_internal(i1 false)
+  ret void
+}
+
+define internal void @test_refscc_internal(i1 %flag, i8* %ptr) {
+; CHECK-NOT: @test_refscc_internal
+entry:
+  br i1 %flag, label %then, label %else
+
+then:
+  call void @test_refscc_internal(i1 false, i8* bitcast (i8* ()* @test_refscc_external to i8*))
+  br label %else
+
+else:
+  ret void
+}
+
+define i8* @test_refscc_external() {
+; CHECK-LABEL: define i8* @test_refscc_external()
+entry:
+  br i1 true, label %then, label %else
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret i8* null
+; CHECK-NEXT:  }
+; CHECK-NOT: @test_refscc_internal
+
+then:
+  ret i8* null
+
+else:
+  ret i8* bitcast (void (i1, i8*)* @test_refscc_internal to i8*)
+}