diff options
Diffstat (limited to 'lib/Transforms/Scalar/RewriteStatepointsForGC.cpp')
-rw-r--r-- | lib/Transforms/Scalar/RewriteStatepointsForGC.cpp | 42 |
1 files changed, 33 insertions, 9 deletions
diff --git a/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp index 1ca77cfec329..44acfc885797 100644 --- a/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp +++ b/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp @@ -125,10 +125,10 @@ struct RewriteStatepointsForGC : public ModulePass { Changed |= runOnFunction(F); if (Changed) { - // stripNonValidAttributesAndMetadata asserts that shouldRewriteStatepointsIn + // stripNonValidData asserts that shouldRewriteStatepointsIn // returns true for at least one function in the module. Since at least // one function changed, we know that the precondition is satisfied. - stripNonValidAttributesAndMetadata(M); + stripNonValidData(M); } return Changed; @@ -146,15 +146,17 @@ struct RewriteStatepointsForGC : public ModulePass { /// metadata implying dereferenceability that are no longer valid/correct after /// RewriteStatepointsForGC has run. This is because semantically, after /// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire - /// heap. stripNonValidAttributesAndMetadata (conservatively) restores + /// heap. stripNonValidData (conservatively) restores /// correctness by erasing all attributes in the module that externally imply /// dereferenceability. Similar reasoning also applies to the noalias /// attributes and metadata. gc.statepoint can touch the entire heap including /// noalias objects. - void stripNonValidAttributesAndMetadata(Module &M); + /// Apart from attributes and metadata, we also remove instructions that imply + /// constant physical memory: llvm.invariant.start. + void stripNonValidData(Module &M); - // Helpers for stripNonValidAttributesAndMetadata - void stripNonValidAttributesAndMetadataFromBody(Function &F); + // Helpers for stripNonValidData + void stripNonValidDataFromBody(Function &F); void stripNonValidAttributesFromPrototype(Function &F); // Certain metadata on instructions are invalid after running RS4GC. @@ -2385,14 +2387,30 @@ void RewriteStatepointsForGC::stripInvalidMetadataFromInstruction(Instruction &I I.dropUnknownNonDebugMetadata(ValidMetadataAfterRS4GC); } -void RewriteStatepointsForGC::stripNonValidAttributesAndMetadataFromBody(Function &F) { +void RewriteStatepointsForGC::stripNonValidDataFromBody(Function &F) { if (F.empty()) return; LLVMContext &Ctx = F.getContext(); MDBuilder Builder(Ctx); + // Set of invariantstart instructions that we need to remove. + // Use this to avoid invalidating the instruction iterator. + SmallVector<IntrinsicInst*, 12> InvariantStartInstructions; + for (Instruction &I : instructions(F)) { + // invariant.start on memory location implies that the referenced memory + // location is constant and unchanging. This is no longer true after + // RewriteStatepointsForGC runs because there can be calls to gc.statepoint + // which frees the entire heap and the presence of invariant.start allows + // the optimizer to sink the load of a memory location past a statepoint, + // which is incorrect. + if (auto *II = dyn_cast<IntrinsicInst>(&I)) + if (II->getIntrinsicID() == Intrinsic::invariant_start) { + InvariantStartInstructions.push_back(II); + continue; + } + if (const MDNode *MD = I.getMetadata(LLVMContext::MD_tbaa)) { assert(MD->getNumOperands() < 5 && "unrecognized metadata shape!"); bool IsImmutableTBAA = @@ -2422,6 +2440,12 @@ void RewriteStatepointsForGC::stripNonValidAttributesAndMetadataFromBody(Functio RemoveNonValidAttrAtIndex(Ctx, CS, AttributeList::ReturnIndex); } } + + // Delete the invariant.start instructions and RAUW undef. + for (auto *II : InvariantStartInstructions) { + II->replaceAllUsesWith(UndefValue::get(II->getType())); + II->eraseFromParent(); + } } /// Returns true if this function should be rewritten by this pass. The main @@ -2438,7 +2462,7 @@ static bool shouldRewriteStatepointsIn(Function &F) { return false; } -void RewriteStatepointsForGC::stripNonValidAttributesAndMetadata(Module &M) { +void RewriteStatepointsForGC::stripNonValidData(Module &M) { #ifndef NDEBUG assert(llvm::any_of(M, shouldRewriteStatepointsIn) && "precondition!"); #endif @@ -2447,7 +2471,7 @@ void RewriteStatepointsForGC::stripNonValidAttributesAndMetadata(Module &M) { stripNonValidAttributesFromPrototype(F); for (Function &F : M) - stripNonValidAttributesAndMetadataFromBody(F); + stripNonValidDataFromBody(F); } bool RewriteStatepointsForGC::runOnFunction(Function &F) { |