path: root/lib/Transforms
diff options
authorChandler Carruth <>2012-10-18 08:05:46 +0000
committerChandler Carruth <>2012-10-18 08:05:46 +0000
commit63a1eb62e4eef1cbdedce5c60c3e1243a071eba1 (patch)
tree176a65087ca155b39732786e150160ed657cc1e0 /lib/Transforms
parent3141d2db037bb3c31a1efd50118df45c1aebbb51 (diff)
Introduce a BarrierNoop pass, a hack designed to allow *some* control
over the implicitly-formed-and-nesting CGSCC pass manager and function pass managers, especially when using them on the opt commandline or using extension points in the module builder. The '-barrier' opt flag (or the pass itself) will create a no-op module pass in the pipeline, resetting the pass manager stack, and allowing the creation of a new pipeline of function passes or CGSCC passes to be created that is independent from any previous pipelines. For example, this can be used to test running two CGSCC passes in independent CGSCC pass managers as opposed to in the same CGSCC pass manager. It also allows us to introduce a further hack into the PassManagerBuilder to separate the O0 pipeline extension passes from the always-inliner's CGSCC pass manager, which they likely do not want to participate in... At the very least none of the Sanitizer passes want this behavior. This fixes a bug with ASan at O0 currently, and I'll commit the ASan test which covers this pass. I'm happy to add a test case that this pass exists and works, but not sure how much time folks would like me to spend adding test cases for the details of its behavior of partition pass managers.... The whole thing is just vile, and mostly intended to unblock ASan, so I'm hoping to rip this all out in a brave new pass manager world. git-svn-id: 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Transforms')
3 files changed, 56 insertions, 0 deletions
diff --git a/lib/Transforms/IPO/BarrierNoopPass.cpp b/lib/Transforms/IPO/BarrierNoopPass.cpp
new file mode 100644
index 00000000000..2e32240621f
--- /dev/null
+++ b/lib/Transforms/IPO/BarrierNoopPass.cpp
@@ -0,0 +1,47 @@
+//===- BarrierNoopPass.cpp - A barrier pass for the pass manager ----------===//
+// The LLVM Compiler Infrastructure
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+// This pass is a nonce pass intended to allow manipulation of the implicitly
+// nesting pass manager. For example, it can be used to cause a CGSCC pass
+// manager to be closed prior to running a new collection of function passes.
+// FIXME: This is a huge HACK. This should be removed when the pass manager's
+// nesting is made explicit instead of implicit.
+#include "llvm/Pass.h"
+#include "llvm/Transforms/IPO.h"
+using namespace llvm;
+namespace {
+/// \brief A nonce module pass used to place a barrier in a pass manager.
+/// There is no mechanism for ending a CGSCC pass manager once one is started.
+/// This prevents extension points from having clear deterministic ordering
+/// when they are phrased as non-module passes.
+class BarrierNoop : public ModulePass {
+ static char ID; // Pass identification.
+ BarrierNoop() : ModulePass(ID) {
+ initializeBarrierNoopPass(*PassRegistry::getPassRegistry());
+ }
+ bool runOnModule(Module &M) { return false; }
+ModulePass *llvm::createBarrierNoopPass() { return new BarrierNoop(); }
+char BarrierNoop::ID = 0;
+INITIALIZE_PASS(BarrierNoop, "barrier", "A No-Op Barrier Pass",
+ false, false)
diff --git a/lib/Transforms/IPO/CMakeLists.txt b/lib/Transforms/IPO/CMakeLists.txt
index 3f6b1de614d..90c1c33e6dc 100644
--- a/lib/Transforms/IPO/CMakeLists.txt
+++ b/lib/Transforms/IPO/CMakeLists.txt
@@ -1,5 +1,6 @@
+ BarrierNoopPass.cpp
diff --git a/lib/Transforms/IPO/PassManagerBuilder.cpp b/lib/Transforms/IPO/PassManagerBuilder.cpp
index 97698caa516..1d8f1e531a0 100644
--- a/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -119,6 +119,14 @@ void PassManagerBuilder::populateModulePassManager(PassManagerBase &MPM) {
Inliner = 0;
+ // FIXME: This is a HACK! The inliner pass above implicitly creates a CGSCC
+ // pass manager, but we don't want to add extensions into that pass manager.
+ // To prevent this we must insert a no-op module pass to reset the pass
+ // manager to get the same behavior as EP_OptimizerLast in non-O0 builds.
+ if (!GlobalExtensions->empty() || !Extensions.empty())
+ MPM.add(createBarrierNoopPass());
addExtensionsToPM(EP_EnabledOnOptLevel0, MPM);