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Reenable this pass, fixing the bugs in it.

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It now correctly deletes unreachable blocks and blocks that are empty.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31000 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-10-17 17:13:52 +00:00
parent 5d04a1af4f
commit c50ffcb7fc
1 changed files with 32 additions and 23 deletions
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55
lib/CodeGen/BranchFolding.cpp
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@ -18,6 +18,7 @@
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/STLExtras.h"
@ -36,39 +37,39 @@ namespace {
FunctionPass *llvm::createBranchFoldingPass() { return new BranchFolder(); }
/// RemoveDeadBlock - Remove the specified dead machine basic block from the
/// function, updating the CFG.
static void RemoveDeadBlock(MachineBasicBlock *MBB) {
assert(MBB->pred_empty() && "MBB must be dead!");
MachineFunction *MF = MBB->getParent();
// drop all successors.
while (!MBB->succ_empty())
MBB->removeSuccessor(MBB->succ_end()-1);
// Remove the block.
MF->getBasicBlockList().erase(MBB);
}
bool BranchFolder::runOnMachineFunction(MachineFunction &MF) {
TII = MF.getTarget().getInstrInfo();
if (!TII) return false;
// DISABLED FOR NOW.
return false;
//MF.dump();
bool EverMadeChange = false;
MadeChange = true;
while (MadeChange) {
MadeChange = false;
for (MachineFunction::iterator MBB = ++MF.begin(), E = MF.end(); MBB != E;
++MBB)
OptimizeBlock(MBB);
// If branches were folded away somehow, do a quick scan and delete any dead
// blocks.
if (MadeChange) {
for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
MachineBasicBlock *MBB = I++;
// Is it dead?
if (MBB->pred_empty()) {
// drop all successors.
while (!MBB->succ_empty())
MBB->removeSuccessor(MBB->succ_end()-1);
MF.getBasicBlockList().erase(MBB);
}
for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
MachineBasicBlock *MBB = I++;
OptimizeBlock(MBB);
// If it is dead, remove it.
if (MBB->pred_empty()) {
RemoveDeadBlock(MBB);
MadeChange = true;
}
}
}
EverMadeChange |= MadeChange;
}
@ -115,14 +116,22 @@ void BranchFolder::OptimizeBlock(MachineFunction::iterator MBB) {
MachineFunction::iterator FallThrough = next(MBB);
if (FallThrough != MBB->getParent()->end()) {
if (FallThrough == MBB->getParent()->end()) {
// TODO: Simplify preds to not branch here if possible!
} else {
// Rewrite all predecessors of the old block to go to the fallthrough
// instead.
while (!MBB->pred_empty()) {
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
ReplaceUsesOfBlockWith(Pred, MBB, FallThrough, TII);
}
// If MBB was the target of a jump table, update jump tables to go to the
// fallthrough instead.
MBB->getParent()->getJumpTableInfo()->ReplaceMBBInJumpTables(MBB,
FallThrough);
MadeChange = true;
}
// TODO: CHANGE STUFF TO NOT BRANCH HERE!
return;
}