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ARM: make branch folder remove unconditional branches 

following jump tables that it earlier inserted.  This
would be OK on other targets but is needed for correctness
only on ARM (constant islands needs to find jump tables).

llvm-svn: 39782
This commit is contained in:
Dale Johannesen 2007-07-12 16:45:35 +00:00
parent ffc337b1e1
commit 85ee72f7ba
2 changed files with 15 additions and 7 deletions
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7
llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
View File

@ -740,14 +740,11 @@ void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB,
delta -= 2;
}
}
// Thumb jump tables require padding. They can be at the end, or
// followed by an unconditional branch.
// Thumb jump tables require padding. They should be at the end;
// following unconditional branches are removed by AnalyzeBranch.
MachineInstr *ThumbJTMI = NULL;
if (prior(MBB->end())->getOpcode() == ARM::tBR_JTr)
ThumbJTMI = prior(MBB->end());
else if (prior(MBB->end()) != MBB->begin() &&
prior(prior(MBB->end()))->getOpcode() == ARM::tBR_JTr)
ThumbJTMI = prior(prior(MBB->end()));
if (ThumbJTMI) {
unsigned newMIOffset = GetOffsetOf(ThumbJTMI);
unsigned oldMIOffset = newMIOffset - delta;

15
llvm/lib/Target/ARM/ARMInstrInfo.cpp
View File

@ -350,8 +350,8 @@ bool ARMInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,MachineBasicBlock *&TBB,
return false;
}
// If the block ends with two B's or tB's, handle it. The second one is not
// executed, so remove it.
// If the block ends with two unconditional branches, handle it. The second
// one is not executed, so remove it.
if ((SecondLastOpc == ARM::B || SecondLastOpc==ARM::tB) &&
(LastOpc == ARM::B || LastOpc == ARM::tB)) {
TBB = SecondLastInst->getOperand(0).getMachineBasicBlock();
@ -360,6 +360,17 @@ bool ARMInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,MachineBasicBlock *&TBB,
return false;
}
// Likewise if it ends with a branch table followed by an unconditional branch.
// The branch folder can create these, and we must get rid of them for
// correctness of Thumb constant islands.
if ((SecondLastOpc == ARM::BR_JTr || SecondLastOpc==ARM::BR_JTm ||
SecondLastOpc == ARM::BR_JTadd || SecondLastOpc==ARM::tBR_JTr) &&
(LastOpc == ARM::B || LastOpc == ARM::tB)) {
I = LastInst;
I->eraseFromParent();
return true;
}
// Otherwise, can't handle this.
return true;
}