Move splitIndirectCriticalEdges() to BasicBlockUtils.h.
Summary:
Move splitIndirectCriticalEdges() from CodeGenPrepare to BasicBlockUtils.h so
that it can be called from other places.
Reviewers: davidxl
Reviewed By: davidxl
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D40750
llvm-svn: 319689
diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 9d3e723..1b01f84 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -18,7 +18,6 @@
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
@@ -86,10 +85,8 @@
#include "llvm/Target/TargetOptions.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/BypassSlowDivision.h"
-#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SimplifyLibCalls.h"
-#include "llvm/Transforms/Utils/ValueMapper.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
@@ -331,7 +328,6 @@
SmallVectorImpl<Instruction *> &SpeculativelyMovedExts);
bool splitBranchCondition(Function &F);
bool simplifyOffsetableRelocate(Instruction &I);
- bool splitIndirectCriticalEdges(Function &F);
};
} // end anonymous namespace
@@ -410,7 +406,7 @@
// Split some critical edges where one of the sources is an indirect branch,
// to help generate sane code for PHIs involving such edges.
- EverMadeChange |= splitIndirectCriticalEdges(F);
+ EverMadeChange |= SplitIndirectBrCriticalEdges(F);
bool MadeChange = true;
while (MadeChange) {
@@ -555,160 +551,6 @@
return DestBB;
}
-// Return the unique indirectbr predecessor of a block. This may return null
-// even if such a predecessor exists, if it's not useful for splitting.
-// If a predecessor is found, OtherPreds will contain all other (non-indirectbr)
-// predecessors of BB.
-static BasicBlock *
-findIBRPredecessor(BasicBlock *BB, SmallVectorImpl<BasicBlock *> &OtherPreds) {
- // If the block doesn't have any PHIs, we don't care about it, since there's
- // no point in splitting it.
- PHINode *PN = dyn_cast<PHINode>(BB->begin());
- if (!PN)
- return nullptr;
-
- // Verify we have exactly one IBR predecessor.
- // Conservatively bail out if one of the other predecessors is not a "regular"
- // terminator (that is, not a switch or a br).
- BasicBlock *IBB = nullptr;
- for (unsigned Pred = 0, E = PN->getNumIncomingValues(); Pred != E; ++Pred) {
- BasicBlock *PredBB = PN->getIncomingBlock(Pred);
- TerminatorInst *PredTerm = PredBB->getTerminator();
- switch (PredTerm->getOpcode()) {
- case Instruction::IndirectBr:
- if (IBB)
- return nullptr;
- IBB = PredBB;
- break;
- case Instruction::Br:
- case Instruction::Switch:
- OtherPreds.push_back(PredBB);
- continue;
- default:
- return nullptr;
- }
- }
-
- return IBB;
-}
-
-// Split critical edges where the source of the edge is an indirectbr
-// instruction. This isn't always possible, but we can handle some easy cases.
-// This is useful because MI is unable to split such critical edges,
-// which means it will not be able to sink instructions along those edges.
-// This is especially painful for indirect branches with many successors, where
-// we end up having to prepare all outgoing values in the origin block.
-//
-// Our normal algorithm for splitting critical edges requires us to update
-// the outgoing edges of the edge origin block, but for an indirectbr this
-// is hard, since it would require finding and updating the block addresses
-// the indirect branch uses. But if a block only has a single indirectbr
-// predecessor, with the others being regular branches, we can do it in a
-// different way.
-// Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr.
-// We can split D into D0 and D1, where D0 contains only the PHIs from D,
-// and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and
-// create the following structure:
-// A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1
-bool CodeGenPrepare::splitIndirectCriticalEdges(Function &F) {
- // Check whether the function has any indirectbrs, and collect which blocks
- // they may jump to. Since most functions don't have indirect branches,
- // this lowers the common case's overhead to O(Blocks) instead of O(Edges).
- SmallSetVector<BasicBlock *, 16> Targets;
- for (auto &BB : F) {
- auto *IBI = dyn_cast<IndirectBrInst>(BB.getTerminator());
- if (!IBI)
- continue;
-
- for (unsigned Succ = 0, E = IBI->getNumSuccessors(); Succ != E; ++Succ)
- Targets.insert(IBI->getSuccessor(Succ));
- }
-
- if (Targets.empty())
- return false;
-
- bool Changed = false;
- for (BasicBlock *Target : Targets) {
- SmallVector<BasicBlock *, 16> OtherPreds;
- BasicBlock *IBRPred = findIBRPredecessor(Target, OtherPreds);
- // If we did not found an indirectbr, or the indirectbr is the only
- // incoming edge, this isn't the kind of edge we're looking for.
- if (!IBRPred || OtherPreds.empty())
- continue;
-
- // Don't even think about ehpads/landingpads.
- Instruction *FirstNonPHI = Target->getFirstNonPHI();
- if (FirstNonPHI->isEHPad() || Target->isLandingPad())
- continue;
-
- BasicBlock *BodyBlock = Target->splitBasicBlock(FirstNonPHI, ".split");
- // It's possible Target was its own successor through an indirectbr.
- // In this case, the indirectbr now comes from BodyBlock.
- if (IBRPred == Target)
- IBRPred = BodyBlock;
-
- // At this point Target only has PHIs, and BodyBlock has the rest of the
- // block's body. Create a copy of Target that will be used by the "direct"
- // preds.
- ValueToValueMapTy VMap;
- BasicBlock *DirectSucc = CloneBasicBlock(Target, VMap, ".clone", &F);
-
- for (BasicBlock *Pred : OtherPreds) {
- // If the target is a loop to itself, then the terminator of the split
- // block needs to be updated.
- if (Pred == Target)
- BodyBlock->getTerminator()->replaceUsesOfWith(Target, DirectSucc);
- else
- Pred->getTerminator()->replaceUsesOfWith(Target, DirectSucc);
- }
-
- // Ok, now fix up the PHIs. We know the two blocks only have PHIs, and that
- // they are clones, so the number of PHIs are the same.
- // (a) Remove the edge coming from IBRPred from the "Direct" PHI
- // (b) Leave that as the only edge in the "Indirect" PHI.
- // (c) Merge the two in the body block.
- BasicBlock::iterator Indirect = Target->begin(),
- End = Target->getFirstNonPHI()->getIterator();
- BasicBlock::iterator Direct = DirectSucc->begin();
- BasicBlock::iterator MergeInsert = BodyBlock->getFirstInsertionPt();
-
- assert(&*End == Target->getTerminator() &&
- "Block was expected to only contain PHIs");
-
- while (Indirect != End) {
- PHINode *DirPHI = cast<PHINode>(Direct);
- PHINode *IndPHI = cast<PHINode>(Indirect);
-
- // Now, clean up - the direct block shouldn't get the indirect value,
- // and vice versa.
- DirPHI->removeIncomingValue(IBRPred);
- Direct++;
-
- // Advance the pointer here, to avoid invalidation issues when the old
- // PHI is erased.
- Indirect++;
-
- PHINode *NewIndPHI = PHINode::Create(IndPHI->getType(), 1, "ind", IndPHI);
- NewIndPHI->addIncoming(IndPHI->getIncomingValueForBlock(IBRPred),
- IBRPred);
-
- // Create a PHI in the body block, to merge the direct and indirect
- // predecessors.
- PHINode *MergePHI =
- PHINode::Create(IndPHI->getType(), 2, "merge", &*MergeInsert);
- MergePHI->addIncoming(NewIndPHI, Target);
- MergePHI->addIncoming(DirPHI, DirectSucc);
-
- IndPHI->replaceAllUsesWith(MergePHI);
- IndPHI->eraseFromParent();
- }
-
- Changed = true;
- }
-
- return Changed;
-}
-
/// Eliminate blocks that contain only PHI nodes, debug info directives, and an
/// unconditional branch. Passes before isel (e.g. LSR/loopsimplify) often split
/// edges in ways that are non-optimal for isel. Start by eliminating these