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Revert 109076. It is wrong and was causing regressions. Add some

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comments explaining why it was wrong.  8225024.

Fix the real problem in 8213383: the code that splits very large
blocks when no other place to put constants can be found was not
considering the case that the block contained a Thumb tablejump.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109282 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen 2010-07-23 22:50:23 +00:00
parent 3144687df7
commit 8086d5800d
1 changed files with 48 additions and 18 deletions
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66
lib/Target/ARM/ARMConstantIslandPass.cpp
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@ -323,6 +323,8 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &MF) {
// constant pool users.
InitialFunctionScan(MF, CPEMIs);
CPEMIs.clear();
DEBUG(dumpBBs());
/// Remove dead constant pool entries.
RemoveUnusedCPEntries();
@ -513,9 +515,10 @@ void ARMConstantIslands::InitialFunctionScan(MachineFunction &MF,
// be right, functions containing these must be 4-byte aligned.
// tBR_JTr expands to a mov pc followed by .align 2 and then the jump
// table entries. So this code checks whether offset of tBR_JTr + 2
// is aligned.
// is aligned. That is held in Offset+MBBSize, which already has
// 2 added in for the size of the mov pc instruction.
MF.EnsureAlignment(2U);
if ((Offset+MBBSize+2)%4 != 0 || HasInlineAsm)
if ((Offset+MBBSize)%4 != 0 || HasInlineAsm)
// FIXME: Add a pseudo ALIGN instruction instead.
MBBSize += 2; // padding
continue; // Does not get an entry in ImmBranches
@ -773,28 +776,54 @@ MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) {
WaterList.insert(IP, OrigBB);
NewWaterList.insert(OrigBB);
// Figure out how large the first NewMBB is. (It cannot
// contain a constpool_entry or tablejump.)
unsigned NewBBSize = 0;
for (MachineBasicBlock::iterator I = NewBB->begin(), E = NewBB->end();
I != E; ++I)
NewBBSize += TII->GetInstSizeInBytes(I);
unsigned OrigBBI = OrigBB->getNumber();
unsigned NewBBI = NewBB->getNumber();
// Set the size of NewBB in BBSizes.
BBSizes[NewBBI] = NewBBSize;
// We removed instructions from UserMBB, subtract that off from its size.
// Add 2 or 4 to the block to count the unconditional branch we added to it.
int delta = isThumb1 ? 2 : 4;
BBSizes[OrigBBI] -= NewBBSize - delta;
// Figure out how large the OrigBB is. As the first half of the original
// block, it cannot contain a tablejump. The size includes
// the new jump we added. (It should be possible to do this without
// recounting everything, but it's very confusing, and this is rarely
// executed.)
unsigned OrigBBSize = 0;
for (MachineBasicBlock::iterator I = OrigBB->begin(), E = OrigBB->end();
I != E; ++I)
OrigBBSize += TII->GetInstSizeInBytes(I);
BBSizes[OrigBBI] = OrigBBSize;
// ...and adjust BBOffsets for NewBB accordingly.
BBOffsets[NewBBI] = BBOffsets[OrigBBI] + BBSizes[OrigBBI];
// Figure out how large the NewMBB is. As the second half of the original
// block, it may contain a tablejump.
unsigned NewBBSize = 0;
for (MachineBasicBlock::iterator I = NewBB->begin(), E = NewBB->end();
I != E; ++I)
NewBBSize += TII->GetInstSizeInBytes(I);
// Set the size of NewBB in BBSizes. It does not include any padding now.
BBSizes[NewBBI] = NewBBSize;
MachineInstr* ThumbJTMI = prior(NewBB->end());
if (ThumbJTMI->getOpcode() == ARM::tBR_JTr) {
// We've added another 2-byte instruction before this tablejump, which
// means we will always need padding if we didn't before, and vice versa.
// The original offset of the jump instruction was:
unsigned OrigOffset = BBOffsets[OrigBBI] + BBSizes[OrigBBI] - delta;
if (OrigOffset%4 == 0) {
// We had padding before and now we don't. No net change in code size.
delta = 0;
} else {
// We didn't have padding before and now we do.
BBSizes[NewBBI] += 2;
delta = 4;
}
}
// All BBOffsets following these blocks must be modified.
AdjustBBOffsetsAfter(NewBB, delta);
if (delta)
AdjustBBOffsetsAfter(NewBB, delta);
return NewBB;
}
@ -921,11 +950,12 @@ void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB,
// Thumb1 jump tables require padding. They should be at the end;
// following unconditional branches are removed by AnalyzeBranch.
// tBR_JTr expands to a mov pc followed by .align 2 and then the jump
// table entries. So this code checks whether offset of tBR_JTr + 2
// is aligned.
// table entries. So this code checks whether offset of tBR_JTr
// is aligned; if it is, the offset of the jump table following the
// instruction will not be aligned, and we need padding.
MachineInstr *ThumbJTMI = prior(MBB->end());
if (ThumbJTMI->getOpcode() == ARM::tBR_JTr) {
unsigned NewMIOffset = GetOffsetOf(ThumbJTMI) + 2;
unsigned NewMIOffset = GetOffsetOf(ThumbJTMI);
unsigned OldMIOffset = NewMIOffset - delta;
if ((OldMIOffset%4) == 0 && (NewMIOffset%4) != 0) {
// remove existing padding