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Fix another case we *don't* want to do this xform.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31861 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-11-18 21:56:39 +00:00
parent 36d68e418d
commit f10a56a86f
1 changed files with 26 additions and 2 deletions
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28
lib/CodeGen/BranchFolding.cpp
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@ -16,6 +16,7 @@
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "branchfolding"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineDebugInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
@ -23,6 +24,7 @@
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
@ -705,17 +707,39 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
if (!PriorCond.empty() && PriorFBB == 0 &&
MachineFunction::iterator(PriorTBB) == FallThrough &&
!CanFallThrough(MBB)) {
bool DoTransform = true;
// We have to be careful that the succs of PredBB aren't both no-successor
// blocks. If neither have successors and if PredBB is the second from
// last block in the function, we'd just keep swapping the two blocks for
// last. Only do the swap if one is clearly better to fall through than
// the other.
if (FallThrough != --MBB->getParent()->end() ||
IsBetterFallthrough(PriorTBB, MBB, *TII)) {
if (FallThrough == --MBB->getParent()->end() &&
!IsBetterFallthrough(PriorTBB, MBB, *TII))
DoTransform = false;
// We don't want to do this transformation if we have control flow like:
// br cond BB2
// BB1:
// ..
// jmp BBX
// BB2:
// ..
// ret
//
// In this case, we could actually be moving the return block *into* a
// loop!
if (DoTransform && !MBB->succ_empty() && !CanFallThrough(PriorTBB))
DoTransform = false;
if (DoTransform) {
// Reverse the branch so we will fall through on the previous true cond.
std::vector<MachineOperand> NewPriorCond(PriorCond);
if (!TII->ReverseBranchCondition(NewPriorCond)) {
DOUT << "\nMoving MBB: " << *MBB;
DOUT << "To make fallthrough to: " << *PriorTBB << "\n";
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond);