Eliminate the unused CodeGenPrepare option to split critical edges.
llvm-svn: 126825
This commit is contained in:
Cameron Zwarich
parent
65b1476031
commit
5dd2aa2615
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@ -58,11 +58,6 @@ STATISTIC(NumMemoryInsts, "Number of memory instructions whose address "
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STATISTIC(NumExtsMoved, "Number of [s|z]ext instructions combined with loads");
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STATISTIC(NumExtUses, "Number of uses of [s|z]ext instructions optimized");
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static cl::opt<bool>
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CriticalEdgeSplit("cgp-critical-edge-splitting",
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cl::desc("Split critical edges during codegen prepare"),
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cl::init(false), cl::Hidden);
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namespace {
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class CodeGenPrepare : public FunctionPass {
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/// TLI - Keep a pointer of a TargetLowering to consult for determining
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@ -144,11 +139,6 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
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// unconditional branch.
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EverMadeChange |= EliminateMostlyEmptyBlocks(F);
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// Now find loop back edges, but only if they are being used to decide which
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// critical edges to split.
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if (CriticalEdgeSplit)
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findLoopBackEdges(F);
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bool MadeChange = true;
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while (MadeChange) {
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MadeChange = false;
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@ -350,110 +340,6 @@ void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) {
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DEBUG(dbgs() << "AFTER:\n" << *DestBB << "\n\n\n");
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}
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/// FindReusablePredBB - Check all of the predecessors of the block DestPHI
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/// lives in to see if there is a block that we can reuse as a critical edge
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/// from TIBB.
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static BasicBlock *FindReusablePredBB(PHINode *DestPHI, BasicBlock *TIBB) {
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BasicBlock *Dest = DestPHI->getParent();
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/// TIPHIValues - This array is lazily computed to determine the values of
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/// PHIs in Dest that TI would provide.
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SmallVector<Value*, 32> TIPHIValues;
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/// TIBBEntryNo - This is a cache to speed up pred queries for TIBB.
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unsigned TIBBEntryNo = 0;
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// Check to see if Dest has any blocks that can be used as a split edge for
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// this terminator.
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for (unsigned pi = 0, e = DestPHI->getNumIncomingValues(); pi != e; ++pi) {
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BasicBlock *Pred = DestPHI->getIncomingBlock(pi);
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// To be usable, the pred has to end with an uncond branch to the dest.
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BranchInst *PredBr = dyn_cast<BranchInst>(Pred->getTerminator());
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if (!PredBr || !PredBr->isUnconditional())
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continue;
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// Must be empty other than the branch and debug info.
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BasicBlock::iterator I = Pred->begin();
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while (isa<DbgInfoIntrinsic>(I))
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I++;
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if (&*I != PredBr)
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continue;
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// Cannot be the entry block; its label does not get emitted.
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if (Pred == &Dest->getParent()->getEntryBlock())
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continue;
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// Finally, since we know that Dest has phi nodes in it, we have to make
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// sure that jumping to Pred will have the same effect as going to Dest in
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// terms of PHI values.
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PHINode *PN;
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unsigned PHINo = 0;
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unsigned PredEntryNo = pi;
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bool FoundMatch = true;
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for (BasicBlock::iterator I = Dest->begin();
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(PN = dyn_cast<PHINode>(I)); ++I, ++PHINo) {
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if (PHINo == TIPHIValues.size()) {
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if (PN->getIncomingBlock(TIBBEntryNo) != TIBB)
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TIBBEntryNo = PN->getBasicBlockIndex(TIBB);
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TIPHIValues.push_back(PN->getIncomingValue(TIBBEntryNo));
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}
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// If the PHI entry doesn't work, we can't use this pred.
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if (PN->getIncomingBlock(PredEntryNo) != Pred)
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PredEntryNo = PN->getBasicBlockIndex(Pred);
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if (TIPHIValues[PHINo] != PN->getIncomingValue(PredEntryNo)) {
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FoundMatch = false;
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break;
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}
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}
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// If we found a workable predecessor, change TI to branch to Succ.
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if (FoundMatch)
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return Pred;
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}
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return 0;
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}
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/// SplitEdgeNicely - Split the critical edge from TI to its specified
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/// successor if it will improve codegen. We only do this if the successor has
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/// phi nodes (otherwise critical edges are ok). If there is already another
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/// predecessor of the succ that is empty (and thus has no phi nodes), use it
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/// instead of introducing a new block.
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static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum,
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SmallSet<std::pair<const BasicBlock*,
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const BasicBlock*>, 8> &BackEdges,
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Pass *P) {
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BasicBlock *TIBB = TI->getParent();
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BasicBlock *Dest = TI->getSuccessor(SuccNum);
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assert(isa<PHINode>(Dest->begin()) &&
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"This should only be called if Dest has a PHI!");
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PHINode *DestPHI = cast<PHINode>(Dest->begin());
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// Do not split edges to EH landing pads.
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if (InvokeInst *Invoke = dyn_cast<InvokeInst>(TI))
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if (Invoke->getSuccessor(1) == Dest)
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return;
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// As a hack, never split backedges of loops. Even though the copy for any
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// PHIs inserted on the backedge would be dead for exits from the loop, we
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// assume that the cost of *splitting* the backedge would be too high.
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if (BackEdges.count(std::make_pair(TIBB, Dest)))
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return;
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if (BasicBlock *ReuseBB = FindReusablePredBB(DestPHI, TIBB)) {
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ProfileInfo *PFI = P->getAnalysisIfAvailable<ProfileInfo>();
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if (PFI)
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PFI->splitEdge(TIBB, Dest, ReuseBB);
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Dest->removePredecessor(TIBB);
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TI->setSuccessor(SuccNum, ReuseBB);
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return;
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}
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SplitCriticalEdge(TI, SuccNum, P, true);
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}
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/// OptimizeNoopCopyExpression - If the specified cast instruction is a noop
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/// copy (e.g. it's casting from one pointer type to another, i32->i8 on PPC),
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/// sink it into user blocks to reduce the number of virtual
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@ -1081,21 +967,8 @@ bool CodeGenPrepare::OptimizeInst(Instruction *I) {
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// across basic blocks and rewrite them to improve basic-block-at-a-time
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// selection.
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bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) {
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bool MadeChange = false;
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// Split all critical edges where the dest block has a PHI.
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if (CriticalEdgeSplit) {
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TerminatorInst *BBTI = BB.getTerminator();
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if (BBTI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(BBTI)) {
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for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i) {
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BasicBlock *SuccBB = BBTI->getSuccessor(i);
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if (isa<PHINode>(SuccBB->begin()) && isCriticalEdge(BBTI, i, true))
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SplitEdgeNicely(BBTI, i, BackEdges, this);
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}
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}
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}
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SunkAddrs.clear();
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bool MadeChange = false;
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CurInstIterator = BB.begin();
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for (BasicBlock::iterator E = BB.end(); CurInstIterator != E; )
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@ -1,4 +1,4 @@
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; RUN: llc < %s -mtriple=armv7-apple-darwin -cgp-critical-edge-splitting=0 | FileCheck %s
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; RUN: llc < %s -mtriple=armv7-apple-darwin | FileCheck %s
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; PHI elimination shouldn't break backedge.
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; rdar://8263994
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@ -1,4 +1,4 @@
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; RUN: llc -verify-machineinstrs -cgp-critical-edge-splitting=0 -mcpu=i386 < %s
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; RUN: llc -verify-machineinstrs -mcpu=i386 < %s
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target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
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target triple = "i386-pc-linux-gnu"
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