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Helpful comment added. Some code cleanup. No functional change.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91479 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2009-12-16 00:08:36 +00:00
parent fe586b3e38
commit c70d331151
1 changed files with 27 additions and 11 deletions
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38
lib/CodeGen/MachineBasicBlock.cpp
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@ -450,14 +450,29 @@ void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
/// CFG to be inserted. If we have proven that MBB can only branch to DestA and
/// DestB, remove any other MBB successors from the CFG. DestA and DestB can
/// be null.
/// DestB, remove any other MBB successors from the CFG. DestA and DestB can be
/// null.
///
/// Besides DestA and DestB, retain other edges leading to LandingPads
/// (currently there can be only one; we don't check or require that here).
/// Note it is possible that DestA and/or DestB are LandingPads.
bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
MachineBasicBlock *DestB,
bool isCond) {
// The values of DestA and DestB frequently come from a call to the
// 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
// values from there.
//
// 1. If both DestA and DestB are null, then the block ends with no branches
// (it falls through to its successor).
// 2. If DestA is set, DestB is null, and isCond is false, then the block ends
// with only an unconditional branch.
// 3. If DestA is set, DestB is null, and isCond is true, then the block ends
// with a conditional branch that falls through to a successor (DestB).
// 4. If DestA and DestB is set and isCond is true, then the block ends with a
// conditional branch followed by an unconditional branch. DestA is the
// 'true' destination and DestB is the 'false' destination.
bool MadeChange = false;
bool AddedFallThrough = false;
@ -483,14 +498,15 @@ bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
MachineBasicBlock::succ_iterator SI = succ_begin();
MachineBasicBlock *OrigDestA = DestA, *OrigDestB = DestB;
while (SI != succ_end()) {
if (*SI == DestA) {
const MachineBasicBlock *MBB = *SI;
if (MBB == DestA) {
DestA = 0;
++SI;
} else if (*SI == DestB) {
} else if (MBB == DestB) {
DestB = 0;
++SI;
} else if ((*SI)->isLandingPad() &&
*SI!=OrigDestA && *SI!=OrigDestB) {
} else if (MBB->isLandingPad() &&
MBB != OrigDestA && MBB != OrigDestB) {
++SI;
} else {
// Otherwise, this is a superfluous edge, remove it.
@ -498,12 +514,12 @@ bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
MadeChange = true;
}
}
if (!AddedFallThrough) {
assert(DestA == 0 && DestB == 0 &&
"MachineCFG is missing edges!");
} else if (isCond) {
if (!AddedFallThrough)
assert(DestA == 0 && DestB == 0 && "MachineCFG is missing edges!");
else if (isCond)
assert(DestA == 0 && "MachineCFG is missing edges!");
}
return MadeChange;
}