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If the false case is the current basic block, then this is a self loop.

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We do not want to emit "Loop: ... brcond Out; br Loop", as it adds an extra
instruction in the loop.  Instead, invert the condition and emit
"Loop: ... br!cond Loop; br Out.

Generalize the fix by moving it from PPCDAGToDAGISel to SelectionDAGLowering.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26231 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2006-02-16 08:27:56 +00:00
parent 8f4880be66
commit 298ebf2bd8
2 changed files with 9 additions and 11 deletions
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9
lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
View File

@ -562,6 +562,15 @@ void SelectionDAGLowering::visitBr(BranchInst &I) {
} else {
std::vector<SDOperand> Ops;
Ops.push_back(getRoot());
// If the false case is the current basic block, then this is a self
// loop. We do not want to emit "Loop: ... brcond Out; br Loop", as it
// adds an extra instruction in the loop. Instead, invert the
// condition and emit "Loop: ... br!cond Loop; br Out.
if (CurMBB == Succ1MBB) {
std::swap(Succ0MBB, Succ1MBB);
SDOperand True = DAG.getConstant(1, Cond.getValueType());
Cond = DAG.getNode(ISD::XOR, Cond.getValueType(), Cond, True);
}
Ops.push_back(Cond);
Ops.push_back(DAG.getBasicBlock(Succ0MBB));
Ops.push_back(DAG.getBasicBlock(Succ1MBB));

11
lib/Target/PowerPC/PPCISelDAGToDAG.cpp
View File

@ -1046,17 +1046,6 @@ void PPCDAGToDAGISel::Select(SDOperand &Result, SDOperand Op) {
if (N->getOpcode() == ISD::BRTWOWAY_CC) {
SDOperand CondTrueBlock = N->getOperand(4);
SDOperand CondFalseBlock = N->getOperand(5);
// If the false case is the current basic block, then this is a self loop.
// We do not want to emit "Loop: ... brcond Out; br Loop", as it adds an
// extra dispatch group to the loop. Instead, invert the condition and
// emit "Loop: ... br!cond Loop; br Out
if (cast<BasicBlockSDNode>(CondFalseBlock)->getBasicBlock() == BB) {
std::swap(CondTrueBlock, CondFalseBlock);
CC = getSetCCInverse(CC,
MVT::isInteger(N->getOperand(2).getValueType()));
}
unsigned Opc = getBCCForSetCC(CC);
SDOperand CB =
SDOperand(CurDAG->getTargetNode(PPC::COND_BRANCH, MVT::Other,