[llvm] r259256 - Add LoopSimplifyCFG pass
via llvm-commits
llvm-commits at lists.llvm.org
Fri Jan 29 15:15:24 PST 2016
Ugh, you’re right, I somehow managed to typo this. I thought I had written cast_or_null. Fixing.
Fiona
> On Jan 29, 2016, at 3:00 PM, Sanjoy Das <sanjoy at playingwithpointers.com> wrote:
>
>
>
> Fiona Glaser via llvm-commits wrote:
>> Author: escha
>> Date: Fri Jan 29 16:35:36 2016
>> New Revision: 259256
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=259256&view=rev
>> Log:
>> Add LoopSimplifyCFG pass
>>
>> Loop transformations can sometimes fail because the loop, while in
>> valid rotated LCSSA form, is not in a canonical CFG form. This is
>> an extremely simple pass that just merges obviously redundant
>> blocks, which can be used to fix some known failure cases. In the
>> future, it may be enhanced with more cases (and have code shared with
>> SimplifyCFG).
>>
>> This allows us to run LoopSimplifyCFG -> LoopRotate -> LoopUnroll,
>> so that SimplifyCFG cleans up the loop before Rotate tries to run.
>>
>> Not currently used in the pass manager, since this pass doesn't do
>> anything unless you can hook it up in an LPM with other loop passes.
>> It'll be added once Chandler cleans up things to allow this.
>>
>> Tested in a custom pipeline out of tree to confirm it works in
>> practice (in addition to the included trivial test).
>>
>> Added:
>> llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
>> llvm/trunk/test/Transforms/LoopSimplifyCFG/
>> llvm/trunk/test/Transforms/LoopSimplifyCFG/merge-header.ll
>> Modified:
>> llvm/trunk/include/llvm/InitializePasses.h
>> llvm/trunk/include/llvm/LinkAllPasses.h
>> llvm/trunk/include/llvm/Transforms/Scalar.h
>> llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt
>> llvm/trunk/lib/Transforms/Scalar/Scalar.cpp
>>
>> Modified: llvm/trunk/include/llvm/InitializePasses.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/InitializePasses.h?rev=259256&r1=259255&r2=259256&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/InitializePasses.h (original)
>> +++ llvm/trunk/include/llvm/InitializePasses.h Fri Jan 29 16:35:36 2016
>> @@ -170,6 +170,7 @@ void initializeLoopInterchangePass(PassR
>> void initializeLoopInstSimplifyPass(PassRegistry&);
>> void initializeLoopRotatePass(PassRegistry&);
>> void initializeLoopSimplifyPass(PassRegistry&);
>> +void initializeLoopSimplifyCFGPass(PassRegistry&);
>> void initializeLoopStrengthReducePass(PassRegistry&);
>> void initializeGlobalMergePass(PassRegistry&);
>> void initializeLoopRerollPass(PassRegistry&);
>>
>> Modified: llvm/trunk/include/llvm/LinkAllPasses.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/LinkAllPasses.h?rev=259256&r1=259255&r2=259256&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/LinkAllPasses.h (original)
>> +++ llvm/trunk/include/llvm/LinkAllPasses.h Fri Jan 29 16:35:36 2016
>> @@ -106,6 +106,7 @@ namespace {
>> (void) llvm::createLoopExtractorPass();
>> (void) llvm::createLoopInterchangePass();
>> (void) llvm::createLoopSimplifyPass();
>> + (void) llvm::createLoopSimplifyCFGPass();
>> (void) llvm::createLoopStrengthReducePass();
>> (void) llvm::createLoopRerollPass();
>> (void) llvm::createLoopUnrollPass();
>>
>> Modified: llvm/trunk/include/llvm/Transforms/Scalar.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Scalar.h?rev=259256&r1=259255&r2=259256&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Transforms/Scalar.h (original)
>> +++ llvm/trunk/include/llvm/Transforms/Scalar.h Fri Jan 29 16:35:36 2016
>> @@ -476,6 +476,13 @@ FunctionPass *createLoopDistributePass()
>> //
>> FunctionPass *createLoopLoadEliminationPass();
>>
>> +//===----------------------------------------------------------------------===//
>> +//
>> +// LoopSimplifyCFG - This pass performs basic CFG simplification on loops,
>> +// primarily to help other loop passes.
>> +//
>> +Pass *createLoopSimplifyCFGPass();
>> +
>> } // End llvm namespace
>>
>> #endif
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt?rev=259256&r1=259255&r2=259256&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt Fri Jan 29 16:35:36 2016
>> @@ -24,6 +24,7 @@ add_llvm_library(LLVMScalarOpts
>> LoopLoadElimination.cpp
>> LoopRerollPass.cpp
>> LoopRotation.cpp
>> + LoopSimplifyCFG.cpp
>> LoopStrengthReduce.cpp
>> LoopUnrollPass.cpp
>> LoopUnswitch.cpp
>>
>> Added: llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp?rev=259256&view=auto
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp (added)
>> +++ llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp Fri Jan 29 16:35:36 2016
>> @@ -0,0 +1,111 @@
>> +//===--------- LoopSimplifyCFG.cpp - Loop CFG Simplification Pass ---------===//
>> +//
>> +// The LLVM Compiler Infrastructure
>> +//
>> +// This file is distributed under the University of Illinois Open Source
>> +// License. See LICENSE.TXT for details.
>> +//
>> +//===----------------------------------------------------------------------===//
>> +//
>> +// This file implements the Loop SimplifyCFG Pass. This pass is responsible for
>> +// basic loop CFG cleanup, primarily to assist other loop passes. If you
>> +// encounter a noncanonical CFG construct that causes another loop pass to
>> +// perform suboptimally, this is the place to fix it up.
>> +//
>> +//===----------------------------------------------------------------------===//
>> +
>> +#include "llvm/Transforms/Scalar.h"
>> +#include "llvm/ADT/SmallVector.h"
>> +#include "llvm/ADT/Statistic.h"
>> +#include "llvm/Analysis/AliasAnalysis.h"
>> +#include "llvm/Analysis/BasicAliasAnalysis.h"
>> +#include "llvm/Analysis/AssumptionCache.h"
>> +#include "llvm/Analysis/DependenceAnalysis.h"
>> +#include "llvm/Analysis/GlobalsModRef.h"
>> +#include "llvm/Analysis/LoopInfo.h"
>> +#include "llvm/Analysis/LoopPass.h"
>> +#include "llvm/Analysis/ScalarEvolution.h"
>> +#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
>> +#include "llvm/Analysis/TargetTransformInfo.h"
>> +#include "llvm/IR/Dominators.h"
>> +#include "llvm/Transforms/Utils/Local.h"
>> +using namespace llvm;
>> +
>> +#define DEBUG_TYPE "loop-simplifycfg"
>> +
>> +namespace {
>> +class LoopSimplifyCFG : public LoopPass {
>> +public:
>> + static char ID; // Pass ID, replacement for typeid
>> + LoopSimplifyCFG() : LoopPass(ID) {
>> + initializeLoopSimplifyCFGPass(*PassRegistry::getPassRegistry());
>> + }
>> +
>> + bool runOnLoop(Loop *L, LPPassManager&) override;
>> +
>> + void getAnalysisUsage(AnalysisUsage&AU) const override {
>> + AU.addRequired<DominatorTreeWrapperPass>();
>> + AU.addRequired<LoopInfoWrapperPass>();
>> +
>> + AU.addPreserved<DominatorTreeWrapperPass>();
>> + AU.addPreserved<LoopInfoWrapperPass>();
>> + AU.addPreserved<GlobalsAAWrapperPass>();
>> + AU.addPreserved<BasicAAWrapperPass>();
>> + AU.addPreserved<AAResultsWrapperPass>();
>> + AU.addPreserved<ScalarEvolutionWrapperPass>();
>> + AU.addPreserved<SCEVAAWrapperPass>();
>> + AU.addPreserved<DependenceAnalysis>();
>> + AU.addPreservedID(LoopSimplifyID);
>> + AU.addPreservedID(LCSSAID);
>> + }
>> +};
>> +}
>> +
>> +char LoopSimplifyCFG::ID = 0;
>> +INITIALIZE_PASS_BEGIN(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
>> + false, false)
>> +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
>> +INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
>> +INITIALIZE_PASS_END(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
>> + false, false)
>> +
>> +Pass *llvm::createLoopSimplifyCFGPass() { return new LoopSimplifyCFG(); }
>> +
>> +static bool simplifyLoopCFG(Loop *L, DominatorTree *DT, LoopInfo *LI) {
>> + bool Changed = false;
>> + // Copy blocks into a temporary array to avoid iterator invalidation issues
>> + // as we remove them.
>> + SmallVector<WeakVH, 16> Blocks(L->blocks());
>> +
>> + for (auto&Block : Blocks) {
>> + // Attempt to merge blocks in the trivial case. Don't modify blocks which
>> + // belong to other loops.
>> + BasicBlock *Succ = cast<BasicBlock>(Block);
>
> cast<> does not allow a null argument, I think you want cast_or_null<> here.
>
>> + if (!Succ)
>> + continue;
>> +
>> + BasicBlock *Pred = Succ->getSinglePredecessor();
>> + if (!Pred || !Pred->getSingleSuccessor() || LI->getLoopFor(Pred) != L)
>> + continue;
>> +
>> + // Pred is going to disappear, so we need to update the loop info.
>> + if (L->getHeader() == Pred)
>> + L->moveToHeader(Succ);
>> + LI->removeBlock(Pred);
>> + MergeBasicBlockIntoOnlyPred(Succ, DT);
>> + Changed = true;
>> + }
>> +
>> + return Changed;
>> +}
>> +
>> +/// runOnLoop - Perform basic CFG simplifications to assist other loop passes.
>> +/// For now, this only attempts to merge blocks in the trivial case.
>> +bool LoopSimplifyCFG::runOnLoop(Loop *L, LPPassManager&) {
>> + if (skipOptnoneFunction(L))
>> + return false;
>> +
>> + DominatorTree *DT =&getAnalysis<DominatorTreeWrapperPass>().getDomTree();
>> + LoopInfo *LI =&getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
>> + return simplifyLoopCFG(L, DT, LI);
>> +}
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/Scalar.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Scalar.cpp?rev=259256&r1=259255&r2=259256&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/Scalar.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/Scalar.cpp Fri Jan 29 16:35:36 2016
>> @@ -84,6 +84,7 @@ void llvm::initializeScalarOpts(PassRegi
>> initializeFloat2IntPass(Registry);
>> initializeLoopDistributePass(Registry);
>> initializeLoopLoadEliminationPass(Registry);
>> + initializeLoopSimplifyCFGPass(Registry);
>> }
>>
>> void LLVMInitializeScalarOpts(LLVMPassRegistryRef R) {
>> @@ -154,6 +155,10 @@ void LLVMAddLoopRerollPass(LLVMPassManag
>> unwrap(PM)->add(createLoopRerollPass());
>> }
>>
>> +void LLVMAddLoopSimplifyCFGPass(LLVMPassManagerRef PM) {
>> + unwrap(PM)->add(createLoopSimplifyCFGPass());
>> +}
>> +
>> void LLVMAddLoopUnrollPass(LLVMPassManagerRef PM) {
>> unwrap(PM)->add(createLoopUnrollPass());
>> }
>>
>> Added: llvm/trunk/test/Transforms/LoopSimplifyCFG/merge-header.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopSimplifyCFG/merge-header.ll?rev=259256&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/LoopSimplifyCFG/merge-header.ll (added)
>> +++ llvm/trunk/test/Transforms/LoopSimplifyCFG/merge-header.ll Fri Jan 29 16:35:36 2016
>> @@ -0,0 +1,34 @@
>> +; RUN: opt -S -loop-simplifycfg< %s | FileCheck %s
>> +
>> +; CHECK-LABEL: foo
>> +; CHECK: entry:
>> +; CHECK-NEXT: br label %[[LOOP:[a-z]+]]
>> +; CHECK: [[LOOP]]:
>> +; CHECK-NEXT: phi
>> +; CHECK-NOT: br label
>> +; CHECK: br i1
>> +define i32 @foo(i32* %P, i64* %Q) {
>> +entry:
>> + br label %outer
>> +
>> +outer: ; preds = %outer.latch2, %entry
>> + %y.2 = phi i32 [ 0, %entry ], [ %y.inc2, %outer.latch2 ]
>> + br label %inner
>> +
>> +inner: ; preds = %outer
>> + store i32 0, i32* %P
>> + store i32 1, i32* %P
>> + store i32 2, i32* %P
>> + %y.inc2 = add nsw i32 %y.2, 1
>> + %exitcond.outer = icmp eq i32 %y.inc2, 3
>> + store i32 %y.2, i32* %P
>> + br i1 %exitcond.outer, label %exit, label %outer.latch2
>> +
>> +outer.latch2: ; preds = %inner
>> + %t = sext i32 %y.inc2 to i64
>> + store i64 %t, i64* %Q
>> + br label %outer
>> +
>> +exit: ; preds = %inner
>> + ret i32 0
>> +}
>>
>>
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