[llvm] a8f1da1 - [LazyCallGraph] Handle spurious ref edges when deleting a dead function
Arthur Eubanks via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 22 15:01:33 PDT 2022
Author: Arthur Eubanks
Date: 2022-09-22T15:01:15-07:00
New Revision: a8f1da128d86d86a3efc1e96e46ace725bf4f3cb
URL: https://github.com/llvm/llvm-project/commit/a8f1da128d86d86a3efc1e96e46ace725bf4f3cb
DIFF: https://github.com/llvm/llvm-project/commit/a8f1da128d86d86a3efc1e96e46ace725bf4f3cb.diff
LOG: [LazyCallGraph] Handle spurious ref edges when deleting a dead function
Spurious ref edges are ref edges that still exist in the call graph even
though the corresponding IR reference no longer exists. This can cause
issues when deleting a dead function which has a spurious ref edge
pointed at it because currently we expect the dead function's RefSCC to
be trivial.
In the case that the dead function's RefSCC is not trivial, remove all
ref edges from other nodes in the RefSCC to it.
Removing a ref edge can result in splitting RefSCCs. There's actually no
reason to revisit those RefSCCs because currently we only run passes on
SCCs, and we've already added all SCCs in the RefSCC to the worklist.
(as opposed to removing the ref edge in
updateCGAndAnalysisManagerForPass() which can modify the call graph of
SCCs we have not visited yet). We also don't expect that RefSCC
refinement will allow us to glean any more information for optimization
use. Also, doing so would drastically increase the complexity of
LazyCallGraph::removeDeadFunction(), requiring us to return a list of
invalidated RefSCCs and new RefSCCs to add to the worklist.
Fixes #56503
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D133907
Added:
llvm/test/Analysis/LazyCallGraph/remove-dead-function-spurious-ref-edge.ll
Modified:
llvm/include/llvm/Analysis/LazyCallGraph.h
llvm/lib/Analysis/LazyCallGraph.cpp
llvm/unittests/Analysis/LazyCallGraphTest.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/LazyCallGraph.h b/llvm/include/llvm/Analysis/LazyCallGraph.h
index ff5518588441a..a25b2166634a3 100644
--- a/llvm/include/llvm/Analysis/LazyCallGraph.h
+++ b/llvm/include/llvm/Analysis/LazyCallGraph.h
@@ -533,6 +533,14 @@ class LazyCallGraph {
/// are necessarily within some actual SCC that nests within it. Since
/// a direct call *is* a reference, there will always be at least one RefSCC
/// around any SCC.
+ ///
+ /// Spurious ref edges, meaning ref edges that still exist in the call graph
+ /// even though the corresponding IR reference no longer exists, are allowed.
+ /// This is mostly to support argument promotion, which can modify a caller to
+ /// no longer pass a function. The only place that needs to specially handle
+ /// this is deleting a dead function/node, otherwise the dead ref edges are
+ /// automatically removed when visiting the function/node no longer containing
+ /// the ref edge.
class RefSCC {
friend class LazyCallGraph;
friend class LazyCallGraph::Node;
@@ -823,8 +831,8 @@ class LazyCallGraph {
/// effort has been made to minimize the overhead of common cases such as
/// self-edges and edge removals which result in a spanning tree with no
/// more cycles.
- SmallVector<RefSCC *, 1> removeInternalRefEdge(Node &SourceN,
- ArrayRef<Node *> TargetNs);
+ [[nodiscard]] SmallVector<RefSCC *, 1>
+ removeInternalRefEdge(Node &SourceN, ArrayRef<Node *> TargetNs);
/// A convenience wrapper around the above to handle trivial cases of
/// inserting a new call edge.
diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index 51459eec255de..a28e8f8092b96 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -1508,10 +1508,6 @@ void LazyCallGraph::removeDeadFunction(Function &F) {
return;
Node &N = *NI->second;
- NodeMap.erase(NI);
-
- // Remove this from the entry edges if present.
- EntryEdges.removeEdgeInternal(N);
// Cannot remove a function which has yet to be visited in the DFS walk, so
// if we have a node at all then we must have an SCC and RefSCC.
@@ -1519,14 +1515,38 @@ void LazyCallGraph::removeDeadFunction(Function &F) {
assert(CI != SCCMap.end() &&
"Tried to remove a node without an SCC after DFS walk started!");
SCC &C = *CI->second;
+ RefSCC *RC = &C.getOuterRefSCC();
+
+ // In extremely rare cases, we can delete a dead function which is still in a
+ // non-trivial RefSCC. This can happen due to spurious ref edges sticking
+ // around after an IR function reference is removed.
+ if (RC->size() != 1) {
+ SmallVector<Node *, 0> NodesInRC;
+ for (SCC &OtherC : *RC) {
+ for (Node &OtherN : OtherC)
+ NodesInRC.push_back(&OtherN);
+ }
+ for (Node *OtherN : NodesInRC) {
+ if ((*OtherN)->lookup(N)) {
+ auto NewRefSCCs =
+ RC->removeInternalRefEdge(*OtherN, ArrayRef<Node *>(&N));
+ // If we've split into multiple RefSCCs, RC is now invalid and the
+ // RefSCC containing C will be
diff erent.
+ if (!NewRefSCCs.empty())
+ RC = &C.getOuterRefSCC();
+ }
+ }
+ }
+
+ NodeMap.erase(NI);
+ EntryEdges.removeEdgeInternal(N);
SCCMap.erase(CI);
- RefSCC &RC = C.getOuterRefSCC();
// This node must be the only member of its SCC as it has no callers, and
// that SCC must be the only member of a RefSCC as it has no references.
// Validate these properties first.
assert(C.size() == 1 && "Dead functions must be in a singular SCC");
- assert(RC.size() == 1 && "Dead functions must be in a singular RefSCC");
+ assert(RC->size() == 1 && "Dead functions must be in a singular RefSCC");
// Finally clear out all the data structures from the node down through the
// components. postorder_ref_scc_iterator will skip empty RefSCCs, so no need
@@ -1535,8 +1555,8 @@ void LazyCallGraph::removeDeadFunction(Function &F) {
N.G = nullptr;
N.F = nullptr;
C.clear();
- RC.clear();
- RC.G = nullptr;
+ RC->clear();
+ RC->G = nullptr;
// Nothing to delete as all the objects are allocated in stable bump pointer
// allocators.
diff --git a/llvm/test/Analysis/LazyCallGraph/remove-dead-function-spurious-ref-edge.ll b/llvm/test/Analysis/LazyCallGraph/remove-dead-function-spurious-ref-edge.ll
new file mode 100644
index 0000000000000..2bc486f541c71
--- /dev/null
+++ b/llvm/test/Analysis/LazyCallGraph/remove-dead-function-spurious-ref-edge.ll
@@ -0,0 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=argpromotion,inline -S %s | FileCheck %s
+
+; argpromo removes @b's parameter (removing @c's reference to @a without updating the ref edge in the call graph), then the inliner inlines @a into @d and attempts to remove @a.
+
+define internal void @a() alwaysinline {
+ call void @e(ptr @c)
+ ret void
+}
+
+define internal void @b(ptr) noinline {
+; CHECK-LABEL: @b(
+; CHECK-NEXT: ret void
+;
+ ret void
+}
+
+define internal void @c() noinline {
+; CHECK-LABEL: @c(
+; CHECK-NEXT: call void @b()
+; CHECK-NEXT: ret void
+;
+ call void @b(ptr @a)
+ ret void
+}
+
+define void @d() {
+; CHECK-LABEL: @d(
+; CHECK-NEXT: call void @e(ptr @c)
+; CHECK-NEXT: ret void
+;
+ call void @a()
+ ret void
+}
+
+declare void @e(ptr);
diff --git a/llvm/unittests/Analysis/LazyCallGraphTest.cpp b/llvm/unittests/Analysis/LazyCallGraphTest.cpp
index d6e73f3a95f2a..ee3c25423ddd8 100644
--- a/llvm/unittests/Analysis/LazyCallGraphTest.cpp
+++ b/llvm/unittests/Analysis/LazyCallGraphTest.cpp
@@ -2092,7 +2092,7 @@ TEST(LazyCallGraphTest, ReplaceNodeFunction) {
EXPECT_EQ(&DN, &(*BN)[DN].getNode());
}
-TEST(LazyCallGraphTest, RemoveFunctionWithSpurriousRef) {
+TEST(LazyCallGraphTest, RemoveFunctionWithSpuriousRef) {
LLVMContext Context;
// A graph with a couple of RefSCCs.
std::unique_ptr<Module> M =
@@ -2173,6 +2173,163 @@ TEST(LazyCallGraphTest, RemoveFunctionWithSpurriousRef) {
EXPECT_EQ(CG.postorder_ref_scc_end(), I);
}
+TEST(LazyCallGraphTest, RemoveFunctionWithSpuriousRefRecursive) {
+ LLVMContext Context;
+ std::unique_ptr<Module> M =
+ parseAssembly(Context, "define void @a(ptr %p) {\n"
+ " store ptr @b, ptr %p\n"
+ " ret void\n"
+ "}\n"
+ "define void @b(ptr %p) {\n"
+ " store ptr @c, ptr %p\n"
+ " ret void\n"
+ "}\n"
+ "define void @c(ptr %p) {\n"
+ " ret void\n"
+ "}\n");
+ LazyCallGraph CG = buildCG(*M);
+
+ LazyCallGraph::Node &AN = CG.get(lookupFunction(*M, "a"));
+ LazyCallGraph::Node &BN = CG.get(lookupFunction(*M, "b"));
+ LazyCallGraph::Node &CN = CG.get(lookupFunction(*M, "c"));
+ AN.populate();
+ BN.populate();
+ CN.populate();
+ // Insert spurious ref edge.
+ CG.insertEdge(CN, AN, LazyCallGraph::Edge::Ref);
+
+ // Force the graph to be fully expanded.
+ CG.buildRefSCCs();
+ auto I = CG.postorder_ref_scc_begin();
+ LazyCallGraph::RefSCC &RC = *I++;
+ EXPECT_EQ(CG.postorder_ref_scc_end(), I);
+
+ ASSERT_EQ(RC.size(), 3);
+
+ EXPECT_EQ(&RC, CG.lookupRefSCC(AN));
+ EXPECT_EQ(&RC, CG.lookupRefSCC(BN));
+ EXPECT_EQ(&RC, CG.lookupRefSCC(CN));
+
+ // Now delete 'a'. There are no uses of this function but there are
+ // spurious references.
+ CG.removeDeadFunction(AN.getFunction());
+
+ // The only observable change should be that the RefSCC is gone from the
+ // postorder sequence.
+ I = CG.postorder_ref_scc_begin();
+ EXPECT_EQ(CG.lookupRefSCC(CN), &*I++);
+ EXPECT_EQ(CG.lookupRefSCC(BN), &*I++);
+ EXPECT_EQ(CG.postorder_ref_scc_end(), I);
+}
+
+TEST(LazyCallGraphTest, RemoveFunctionWithSpuriousRefRecursive2) {
+ LLVMContext Context;
+ std::unique_ptr<Module> M =
+ parseAssembly(Context, "define void @a(ptr %p) {\n"
+ " store ptr @b, ptr %p\n"
+ " ret void\n"
+ "}\n"
+ "define void @b(ptr %p) {\n"
+ " store ptr @c, ptr %p\n"
+ " ret void\n"
+ "}\n"
+ "define void @c(ptr %p) {\n"
+ " store ptr @b, ptr %p\n"
+ " store ptr @d, ptr %p\n"
+ " ret void\n"
+ "}\n"
+ "define void @d(ptr %p) {\n"
+ " ret void\n"
+ "}\n");
+ LazyCallGraph CG = buildCG(*M);
+
+ LazyCallGraph::Node &AN = CG.get(lookupFunction(*M, "a"));
+ LazyCallGraph::Node &BN = CG.get(lookupFunction(*M, "b"));
+ LazyCallGraph::Node &CN = CG.get(lookupFunction(*M, "c"));
+ LazyCallGraph::Node &DN = CG.get(lookupFunction(*M, "d"));
+ AN.populate();
+ BN.populate();
+ CN.populate();
+ DN.populate();
+ // Insert spurious ref edge.
+ CG.insertEdge(DN, AN, LazyCallGraph::Edge::Ref);
+
+ // Force the graph to be fully expanded.
+ CG.buildRefSCCs();
+ auto I = CG.postorder_ref_scc_begin();
+ LazyCallGraph::RefSCC &RC = *I++;
+ EXPECT_EQ(CG.postorder_ref_scc_end(), I);
+
+ ASSERT_EQ(4, RC.size());
+
+ EXPECT_EQ(&RC, CG.lookupRefSCC(AN));
+ EXPECT_EQ(&RC, CG.lookupRefSCC(BN));
+ EXPECT_EQ(&RC, CG.lookupRefSCC(CN));
+ EXPECT_EQ(&RC, CG.lookupRefSCC(DN));
+
+ // Now delete 'a'. There are no uses of this function but there are
+ // spurious references.
+ CG.removeDeadFunction(AN.getFunction());
+
+ // The only observable change should be that the RefSCC is gone from the
+ // postorder sequence.
+ I = CG.postorder_ref_scc_begin();
+ EXPECT_EQ(CG.lookupRefSCC(DN), &*I++);
+ EXPECT_EQ(CG.lookupRefSCC(CN), &*I);
+ EXPECT_EQ(CG.lookupRefSCC(BN), &*I++);
+ EXPECT_EQ(CG.postorder_ref_scc_end(), I);
+}
+
+TEST(LazyCallGraphTest, RemoveFunctionWithSpuriousRefRecursive3) {
+ LLVMContext Context;
+ std::unique_ptr<Module> M =
+ parseAssembly(Context, "define void @a(ptr %p) {\n"
+ " store ptr @b, ptr %p\n"
+ " ret void\n"
+ "}\n"
+ "define void @b(ptr %p) {\n"
+ " store ptr @c, ptr %p\n"
+ " ret void\n"
+ "}\n"
+ "define void @c(ptr %p) {\n"
+ " ret void\n"
+ "}\n");
+ LazyCallGraph CG = buildCG(*M);
+
+ LazyCallGraph::Node &AN = CG.get(lookupFunction(*M, "a"));
+ LazyCallGraph::Node &BN = CG.get(lookupFunction(*M, "b"));
+ LazyCallGraph::Node &CN = CG.get(lookupFunction(*M, "c"));
+ AN.populate();
+ BN.populate();
+ CN.populate();
+ // Insert spurious ref edges.
+ CG.insertEdge(CN, AN, LazyCallGraph::Edge::Ref);
+ CG.insertEdge(BN, AN, LazyCallGraph::Edge::Ref);
+
+ // Force the graph to be fully expanded.
+ CG.buildRefSCCs();
+ auto I = CG.postorder_ref_scc_begin();
+ LazyCallGraph::RefSCC &RC = *I++;
+ EXPECT_EQ(CG.postorder_ref_scc_end(), I);
+
+ ASSERT_EQ(RC.size(), 3);
+
+ EXPECT_EQ(&RC, CG.lookupRefSCC(AN));
+ EXPECT_EQ(&RC, CG.lookupRefSCC(BN));
+ EXPECT_EQ(&RC, CG.lookupRefSCC(CN));
+
+ // Now delete 'a'. There are no uses of this function but there are
+ // spurious references.
+ CG.removeDeadFunction(AN.getFunction());
+
+ // The only observable change should be that the RefSCC is gone from the
+ // postorder sequence.
+ I = CG.postorder_ref_scc_begin();
+ EXPECT_EQ(CG.lookupRefSCC(CN), &*I++);
+ EXPECT_EQ(CG.lookupRefSCC(BN), &*I++);
+ EXPECT_EQ(CG.postorder_ref_scc_end(), I);
+}
+
TEST(LazyCallGraphTest, AddSplitFunction1) {
LLVMContext Context;
std::unique_ptr<Module> M = parseAssembly(Context, "define void @f() {\n"
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