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Revert "[CGP] Split some critical edges coming out of indirect branches"
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This reverts commit r296149 as it leads to crashes when compiling for
PPC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296295 91177308-0d34-0410-b5e6-96231b3b80d8
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@djasper-gh
djasper-gh committed Feb 26, 2017
1 parent 1aaf55c commit e5e8f2a
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Showing 5 changed files with 13 additions and 435 deletions.
155 changes: 0 additions & 155 deletions lib/CodeGen/CodeGenPrepare.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,12 +15,10 @@

#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
Expand Down Expand Up @@ -55,10 +53,8 @@
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/BuildLibCalls.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"
using namespace llvm;
using namespace llvm::PatternMatch;

Expand Down Expand Up @@ -226,7 +222,6 @@ class TypePromotionTransaction;
unsigned CreatedInstCost);
bool splitBranchCondition(Function &F);
bool simplifyOffsetableRelocate(Instruction &I);
bool splitIndirectCriticalEdges(Function &F);
};
}

Expand Down Expand Up @@ -301,10 +296,6 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
if (!DisableBranchOpts)
EverMadeChange |= splitBranchCondition(F);

// 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);

bool MadeChange = true;
while (MadeChange) {
MadeChange = false;
Expand Down Expand Up @@ -438,152 +429,6 @@ BasicBlock *CodeGenPrepare::findDestBlockOfMergeableEmptyBlock(BasicBlock *BB) {
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 (!IBRPred)
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)
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
Expand Down
1 change: 0 additions & 1 deletion test/CodeGen/ARM/indirectbr.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,6 @@ L3: ; preds = %L4, %bb2
br label %L2

L2: ; preds = %L3, %bb2
; THUMB-LABEL: %L1.clone
; THUMB: muls
%res.2 = phi i32 [ %res.1, %L3 ], [ 1, %bb2 ] ; <i32> [#uses=1]
%phitmp = mul i32 %res.2, 6 ; <i32> [#uses=1]
Expand Down
2 changes: 1 addition & 1 deletion test/CodeGen/MSP430/indirectbr2.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ define internal i16 @foo(i16 %i) nounwind {
entry:
%tmp1 = getelementptr inbounds [5 x i8*], [5 x i8*]* @C.0.2070, i16 0, i16 %i ; <i8**> [#uses=1]
%gotovar.4.0 = load i8*, i8** %tmp1, align 4 ; <i8*> [#uses=1]
; CHECK: br .LC.0.2070(r15)
; CHECK: br .LC.0.2070(r12)
indirectbr i8* %gotovar.4.0, [label %L5, label %L4, label %L3, label %L2, label %L1]

L5: ; preds = %bb2
Expand Down
36 changes: 12 additions & 24 deletions test/CodeGen/PowerPC/indirectbr.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -17,35 +17,23 @@ entry:
bb2: ; preds = %entry, %bb3
%gotovar.4.0 = phi i8* [ %gotovar.4.0.pre, %bb3 ], [ %0, %entry ] ; <i8*> [#uses=1]
; PIC: mtctr
; PIC-NEXT: li
; PIC-NEXT: li
; PIC-NEXT: li
; PIC-NEXT: li
; PIC-NEXT: bctr
; PIC: li
; PIC: b LBB
; PIC: li
; PIC: b LBB
; PIC: li
; PIC: b LBB
; PIC: li
; PIC: b LBB
; STATIC: mtctr
; STATIC-NEXT: li
; STATIC-NEXT: li
; STATIC-NEXT: li
; STATIC-NEXT: li
; STATIC-NEXT: bctr
; STATIC: li
; STATIC: b LBB
; STATIC: li
; STATIC: b LBB
; STATIC: li
; STATIC: b LBB
; STATIC: li
; STATIC: b LBB
; PPC64: mtctr
; PPC64-NEXT: li
; PPC64-NEXT: li
; PPC64-NEXT: li
; PPC64-NEXT: li
; PPC64-NEXT: bctr
; PPC64: li
; PPC64: b LBB
; PPC64: li
; PPC64: b LBB
; PPC64: li
; PPC64: b LBB
; PPC64: li
; PPC64: b LBB
indirectbr i8* %gotovar.4.0, [label %L5, label %L4, label %L3, label %L2, label %L1]

bb3: ; preds = %entry
Expand Down
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