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improve deletion of blocks that just contain branches by knowing that

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the pred block doesn't fall through into them if it's a jumptable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31263 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-10-28 17:32:47 +00:00
parent c24ff8ed12
commit cf420cca57
1 changed files with 38 additions and 33 deletions
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71
lib/CodeGen/BranchFolding.cpp
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@ -534,43 +534,48 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
// completely eliminate the block is when the block before this one
// falls through into MBB and we can't understand the prior block's branch
// condition.
if (MBB->empty() && (!PriorUnAnalyzable || !PrevBB.isSuccessor(MBB))) {
// If the prior block falls through into us, turn it into an
// explicit branch to us to make updates simpler.
if (PrevBB.isSuccessor(MBB) && PriorTBB != MBB && PriorFBB != MBB) {
if (PriorTBB == 0) {
assert(PriorCond.empty() && PriorFBB == 0 && "Bad branch analysis");
PriorTBB = MBB;
} else {
assert(PriorFBB == 0 && "Machine CFG out of date!");
PriorFBB = MBB;
if (MBB->empty()) {
bool PredHasNoFallThrough = TII->BlockHasNoFallThrough(PrevBB);
if (PredHasNoFallThrough || !PriorUnAnalyzable ||
!PrevBB.isSuccessor(MBB)) {
// If the prior block falls through into us, turn it into an
// explicit branch to us to make updates simpler.
if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
PriorTBB != MBB && PriorFBB != MBB) {
if (PriorTBB == 0) {
assert(PriorCond.empty() && PriorFBB == 0 && "Bad branch analysis");
PriorTBB = MBB;
} else {
assert(PriorFBB == 0 && "Machine CFG out of date!");
PriorFBB = MBB;
}
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond);
}
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond);
}
// Iterate through all the predecessors, revectoring each in-turn.
MachineBasicBlock::pred_iterator PI = MBB->pred_begin();
bool DidChange = false;
bool HasBranchToSelf = false;
while (PI != MBB->pred_end()) {
if (*PI == MBB) {
// If this block has an uncond branch to itself, leave it.
++PI;
HasBranchToSelf = true;
} else {
DidChange = true;
ReplaceUsesOfBlockWith(*PI, MBB, CurTBB, TII);
// Iterate through all the predecessors, revectoring each in-turn.
MachineBasicBlock::pred_iterator PI = MBB->pred_begin();
bool DidChange = false;
bool HasBranchToSelf = false;
while (PI != MBB->pred_end()) {
if (*PI == MBB) {
// If this block has an uncond branch to itself, leave it.
++PI;
HasBranchToSelf = true;
} else {
DidChange = true;
ReplaceUsesOfBlockWith(*PI, MBB, CurTBB, TII);
}
}
}
// Change any jumptables to go to the new MBB.
MBB->getParent()->getJumpTableInfo()->ReplaceMBBInJumpTables(MBB,
CurTBB);
if (DidChange) {
++NumBranchOpts;
MadeChange = true;
if (!HasBranchToSelf) return;
// Change any jumptables to go to the new MBB.
MBB->getParent()->getJumpTableInfo()->ReplaceMBBInJumpTables(MBB,
CurTBB);
if (DidChange) {
++NumBranchOpts;
MadeChange = true;
if (!HasBranchToSelf) return;
}
}
}