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make the previous change more aggressive, moving any block with no fallthrough.

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This speeds up yacr2 by 7% on a core2.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31856 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-11-18 21:30:35 +00:00
parent a7bef4a4e4
commit 154e104718
1 changed files with 11 additions and 9 deletions
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20
lib/CodeGen/BranchFolding.cpp
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@ -593,15 +593,15 @@ bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) {
static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
MachineBasicBlock *MBB2,
const TargetInstrInfo &TII) {
// Right now, we use a simple heuristic. If MBB ends with a return, and
// MBB2 doesn't, we prefer to fall through into MBB1. This allows us to
// Right now, we use a simple heuristic. If MBB2 ends with a call, and
// MBB1 doesn't, we prefer to fall through into MBB1. This allows us to
// optimize branches that branch to either a return block or an assert block
// into a fallthrough to the return.
if (MBB1->empty() || MBB2->empty()) return false;
MachineInstr *MBB1I = --MBB1->end();
MachineInstr *MBB2I = --MBB2->end();
return TII.isReturn(MBB1I->getOpcode()) && !TII.isReturn(MBB2I->getOpcode());
return TII.isCall(MBB2I->getOpcode()) && !TII.isCall(MBB1I->getOpcode());
}
/// OptimizeBlock - Analyze and optimize control flow related to the specified
@ -694,15 +694,17 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
}
}
// If this block has no successors (e.g. it is a return block or ends with
// a call to a no-return function like abort or __cxa_throw) and if the pred
// falls through into this block, and if it would otherwise fall through
// into the block after this, move this block to the end of the function.
// If this block doesn't fall through (e.g. it ends with an uncond branch or
// has no successors) and if the pred falls through into this block, and if
// it would otherwise fall through into the block after this, move this
// block to the end of the function.
//
// We consider it more likely that execution will stay in the function (e.g.
// due to loops) than it is to exit it. This asserts in loops etc, moving
// the assert condition out of the loop body.
if (MBB->succ_empty() && !PriorCond.empty() && PriorFBB == 0 &&
MachineFunction::iterator(PriorTBB) == FallThrough) {
if (!PriorCond.empty() && PriorFBB == 0 &&
MachineFunction::iterator(PriorTBB) == FallThrough &&
!CanFallThrough(MBB)) {
// 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