[StripGCRelocates] New pass to remove gc.relocates added by RS4GC
Summary:
Utility pass to remove gc.relocates created by rewrite statepoints for GC.
With respect to safepoint verification, the IR generated would be incorrect, and cannot run
as such.
This would be a single transformation on the final optimized IR.
The benefit of the pass is for easy analysis when the IRs are 'polluted' by too
many gc.relocates.
Added tests.
test run: All RS4GC tests with -verify option. Local downstream tests on large
IR files. This also works when the pointer being gc.relocated is another
gc.relocate.
Reviewers: sanjoy, reames
Subscribers: beanz, mgorny, llvm-commits
Differential Revision: https://reviews.llvm.org/D25096
llvm-svn: 284855
diff --git a/llvm/lib/Transforms/Utils/StripGCRelocates.cpp b/llvm/lib/Transforms/Utils/StripGCRelocates.cpp
new file mode 100644
index 0000000..f3d3fad
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/StripGCRelocates.cpp
@@ -0,0 +1,80 @@
+//===- StripGCRelocates.cpp - Remove gc.relocates inserted by RewriteStatePoints===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This is a little utility pass that removes the gc.relocates inserted by
+// RewriteStatepointsForGC. Note that the generated IR is incorrect,
+// but this is useful as a single pass in itself, for analysis of IR, without
+// the GC.relocates. The statepoint and gc.result instrinsics would still be
+// present.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Statepoint.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+namespace {
+struct StripGCRelocates : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ StripGCRelocates() : FunctionPass(ID) {
+ initializeStripGCRelocatesPass(*PassRegistry::getPassRegistry());
+ }
+
+ void getAnalysisUsage(AnalysisUsage &Info) const override {}
+
+ bool runOnFunction(Function &F) override;
+
+};
+char StripGCRelocates::ID = 0;
+}
+
+bool StripGCRelocates::runOnFunction(Function &F) {
+ // Nothing to do for declarations.
+ if (F.isDeclaration())
+ return false;
+ SmallVector<GCRelocateInst *, 20> GCRelocates;
+ // TODO: We currently do not handle gc.relocates that are in landing pads,
+ // i.e. not bound to a single statepoint token.
+ for (Instruction &I : instructions(F)) {
+ if (auto *GCR = dyn_cast<GCRelocateInst>(&I))
+ if (isStatepoint(GCR->getOperand(0)))
+ GCRelocates.push_back(GCR);
+ }
+ // All gc.relocates are bound to a single statepoint token. The order of
+ // visiting gc.relocates for deletion does not matter.
+ for (GCRelocateInst *GCRel : GCRelocates) {
+ Value *OrigPtr = GCRel->getDerivedPtr();
+ Value *ReplaceGCRel = OrigPtr;
+
+ // All gc_relocates are i8 addrspace(1)* typed, we need a bitcast from i8
+ // addrspace(1)* to the type of the OrigPtr, if the are not the same.
+ if (GCRel->getType() != OrigPtr->getType())
+ ReplaceGCRel = new BitCastInst(OrigPtr, GCRel->getType(), "cast", GCRel);
+
+ // Replace all uses of gc.relocate and delete the gc.relocate
+ // There maybe unncessary bitcasts back to the OrigPtr type, an instcombine
+ // pass would clear this up.
+ GCRel->replaceAllUsesWith(ReplaceGCRel);
+ GCRel->eraseFromParent();
+ }
+ return !GCRelocates.empty();
+}
+
+INITIALIZE_PASS(StripGCRelocates, "strip-gc-relocates",
+ "Strip gc.relocates inserted through RewriteStatepointsForGC",
+ true, false)
+FunctionPass *llvm::createStripGCRelocatesPass() {
+ return new StripGCRelocates();
+}