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Fix PHIElimination optimization that uses MBB->getBasicBlock.

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The BasicBlock associated with a MachineBasicBlock does not necessarily
correspond to the code in the MBB.

Don't insert a new IR BasicBlock when splitting critical edges. We are not
supposed to modify the IR during codegen, and we should be able to do just
fine with a NULL BB.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88707 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2009-11-13 21:56:15 +00:00
parent ce727d0da0
commit 1222287543
2 changed files with 23 additions and 34 deletions
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48
lib/CodeGen/PHIElimination.cpp
View File

@ -15,8 +15,6 @@
#define DEBUG_TYPE "phielim"
#include "PHIElimination.h"
#include "llvm/BasicBlock.h"
#include "llvm/Instructions.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
@ -126,26 +124,28 @@ static bool isSourceDefinedByImplicitDef(const MachineInstr *MPhi,
return true;
}
// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg.
// This needs to be after any def or uses of SrcReg, but before any subsequent
// point where control flow might jump out of the basic block.
// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg
// when following the CFG edge to SuccMBB. This needs to be after any def of
// SrcReg, but before any subsequent point where control flow might jump out of
// the basic block.
MachineBasicBlock::iterator
llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB,
MachineBasicBlock &SuccMBB,
unsigned SrcReg) {
// Handle the trivial case trivially.
if (MBB.empty())
return MBB.begin();
// If this basic block does not contain an invoke, then control flow always
// reaches the end of it, so place the copy there. The logic below works in
// this case too, but is more expensive.
if (!isa<InvokeInst>(MBB.getBasicBlock()->getTerminator()))
// Usually, we just want to insert the copy before the first terminator
// instruction. However, for the edge going to a landing pad, we must insert
// the copy before the call/invoke instruction.
if (!SuccMBB.isLandingPad())
return MBB.getFirstTerminator();
// Discover any definition/uses in this basic block.
// Discover any definitions in this basic block.
SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg),
RE = MRI->reg_end(); RI != RE; ++RI) {
for (MachineRegisterInfo::def_iterator RI = MRI->def_begin(SrcReg),
RE = MRI->def_end(); RI != RE; ++RI) {
MachineInstr *DefUseMI = &*RI;
if (DefUseMI->getParent() == &MBB)
DefUsesInMBB.insert(DefUseMI);
@ -153,14 +153,14 @@ llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB,
MachineBasicBlock::iterator InsertPoint;
if (DefUsesInMBB.empty()) {
// No def/uses. Insert the copy at the start of the basic block.
// No defs. Insert the copy at the start of the basic block.
InsertPoint = MBB.begin();
} else if (DefUsesInMBB.size() == 1) {
// Insert the copy immediately after the definition/use.
// Insert the copy immediately after the def.
InsertPoint = *DefUsesInMBB.begin();
++InsertPoint;
} else {
// Insert the copy immediately after the last definition/use.
// Insert the copy immediately after the last def.
InsertPoint = MBB.end();
while (!DefUsesInMBB.count(&*--InsertPoint)) {}
++InsertPoint;
@ -272,7 +272,8 @@ void llvm::PHIElimination::LowerAtomicPHINode(
// Find a safe location to insert the copy, this may be the first terminator
// in the block (or end()).
MachineBasicBlock::iterator InsertPos = FindCopyInsertPoint(opBlock, SrcReg);
MachineBasicBlock::iterator InsertPos =
FindCopyInsertPoint(opBlock, MBB, SrcReg);
// Insert the copy.
TII->copyRegToReg(opBlock, InsertPos, IncomingReg, SrcReg, RC, RC);
@ -427,21 +428,8 @@ MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A,
assert(A && B && "Missing MBB end point");
++NumSplits;
BasicBlock *ABB = const_cast<BasicBlock*>(A->getBasicBlock());
BasicBlock *BBB = const_cast<BasicBlock*>(B->getBasicBlock());
assert(ABB && BBB && "End points must have a basic block");
BasicBlock *BB = BasicBlock::Create(BBB->getContext(),
ABB->getName() + "." + BBB->getName() +
"_phi_edge");
Function *F = ABB->getParent();
F->getBasicBlockList().insert(F->end(), BB);
BranchInst::Create(BBB, BB);
// We could do more here to produce correct IR, compare
// llvm::SplitCriticalEdge
MachineFunction *MF = A->getParent();
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(BB);
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
MF->push_back(NMBB);
DEBUG(errs() << "PHIElimination splitting critical edge:"
" BB#" << A->getNumber()

9
lib/CodeGen/PHIElimination.h
View File

@ -110,11 +110,12 @@ namespace llvm {
MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
MachineBasicBlock *B);
// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
// SrcReg. This needs to be after any def or uses of SrcReg, but before
// any subsequent point where control flow might jump out of the basic
// block.
/// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
/// SrcReg when following the CFG edge to SuccMBB. This needs to be after
/// any def of SrcReg, but before any subsequent point where control flow
/// might jump out of the basic block.
MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
MachineBasicBlock &SuccMBB,
unsigned SrcReg);
// SkipPHIsAndLabels - Copies need to be inserted after phi nodes and