[llvm] 26f3563 - [LazyCallGraph] Fix ambiguous index value

[Brian Gesiak via llvm-commits]

Author: Brian Gesiak
Date: 2020-02-18T23:32:55-05:00
New Revision: 26f356350bd56f5418e5fae230b1a6931774c8f1

URL: https://github.com/llvm/llvm-project/commit/26f356350bd56f5418e5fae230b1a6931774c8f1
DIFF: https://github.com/llvm/llvm-project/commit/26f356350bd56f5418e5fae230b1a6931774c8f1.diff

LOG: [LazyCallGraph] Fix ambiguous index value

After having committed https://reviews.llvm.org/D72226, 2 buildbots
running GCC 5.4.0 began failing. The cause was the order in which those
compilers evaluated the left- and right-hand sides of the expression
`RC.SCCIndices[C] = RC.SCCIndices.size();`. This commit splits the
expression into multiple statements to avoid ambiguity, and adds a test
case that exercises the code that caused the test failures on those
older compilers (which was originally included in the reviewed patch,
https://reviews.llvm.org/D72226).

Added: 
    

Modified: 
    llvm/lib/Analysis/LazyCallGraph.cpp
    llvm/unittests/Analysis/CGSCCPassManagerTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index 0d647cba7092..1ce20d1db156 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -1576,7 +1576,8 @@ void LazyCallGraph::addNewFunctionIntoRefSCC(Function &NewF, RefSCC &RC) {
   auto *C = createSCC(RC, SmallVector<Node *, 1>());
   addNodeToSCC(*C, N);
 
-  RC.SCCIndices[C] = RC.SCCIndices.size();
+  auto Index = RC.SCCIndices.size();
+  RC.SCCIndices[C] = Index;
   RC.SCCs.push_back(C);
 }
 

diff  --git a/llvm/unittests/Analysis/CGSCCPassManagerTest.cpp b/llvm/unittests/Analysis/CGSCCPassManagerTest.cpp
index b8983901269b..0ed3ca353507 100644
--- a/llvm/unittests/Analysis/CGSCCPassManagerTest.cpp
+++ b/llvm/unittests/Analysis/CGSCCPassManagerTest.cpp
@@ -1685,5 +1685,55 @@ TEST_F(CGSCCPassManagerTest, TestUpdateCGAndAnalysisManagerForPasses10) {
   MPM.run(*M, MAM);
 }
 
+TEST_F(CGSCCPassManagerTest, TestInsertionOfNewRefSCC) {
+  std::unique_ptr<Module> M = parseIR("define void @f() {\n"
+                                      "entry:\n"
+                                      "  call void @f()\n"
+                                      "  ret void\n"
+                                      "}\n");
+
+  CGSCCPassManager CGPM(/*DebugLogging*/ true);
+  CGPM.addPass(LambdaSCCPassNoPreserve(
+      [&](LazyCallGraph::SCC &C, CGSCCAnalysisManager &AM, LazyCallGraph &CG,
+          CGSCCUpdateResult &UR) {
+        for (auto &N : C) {
+          auto &F = N.getFunction();
+          if (F.getName() != "f")
+            continue;
+          auto *Call = dyn_cast<CallInst>(F.begin()->begin());
+          if (!Call || Call->getCalledFunction()->getName() != "f")
+            continue;
+
+          // Create a new function 'g'.
+          auto *G = Function::Create(F.getFunctionType(), F.getLinkage(),
+                                     F.getAddressSpace(), "g", F.getParent());
+          BasicBlock::Create(F.getParent()->getContext(), "entry", G);
+          // Instruct the LazyCallGraph to create a new node for 'g', as the
+          // single node in a new SCC, into the call graph. As a result
+          // the call graph is composed of a single RefSCC with two SCCs:
+          // [(f), (g)].
+          CG.addNewFunctionIntoRefSCC(*G, C.getOuterRefSCC());
+
+          // "Demote" the 'f -> f' call egde to a ref edge.
+          // 1. Erase the call edge from 'f' to 'f'.
+          Call->eraseFromParent();
+          // 2. Insert a ref edge from 'f' to 'f'.
+          (void)CastInst::CreatePointerCast(&F,
+                                            Type::getInt8PtrTy(F.getContext()),
+                                            "f.ref", &*F.begin()->begin());
+
+          ASSERT_NO_FATAL_FAILURE(
+              updateCGAndAnalysisManagerForCGSCCPass(CG, C, N, AM, UR))
+              << "Updating the call graph with a demoted, self-referential "
+                 "call edge 'f -> f', and a newly inserted ref edge 'f -> g', "
+                 "caused a fatal failure";
+        }
+      }));
+
+  ModulePassManager MPM(/*DebugLogging*/ true);
+  MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(std::move(CGPM)));
+  MPM.run(*M, MAM);
+}
+
 #endif
 } // namespace