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Temporary workaround for a bad bug introduced by r121082 which replaced 

t2LDRpci with t2LDRi12.
There are a couple of problems with this.
1. The encoding for the literal and immediate constant are different.
   Note bit 7 of the literal case is 'U' so it can be negative.
2. t2LDRi12 is now narrowed to tLDRpci before constant island pass is run.
   So we end up never using the Thumb2 instruction, which ends up creating a
   lot more constant islands.

llvm-svn: 125074
This commit is contained in:
Evan Cheng 2011-02-08 03:07:03 +00:00
parent b0a3ecb41c
commit 558ccef74f
2 changed files with 19 additions and 8 deletions
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14
llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
View File

@ -1576,6 +1576,16 @@ bool ARMConstantIslands::OptimizeThumb2Instructions(MachineFunction &MF) {
Scale = 4;
}
break;
case ARM::t2LDRi12:
// FIXME: Temporary workaround for a bug introduced by r121082.
// We should use t2LDRpci for loads from constantpools.
if (isARMLowRegister(U.MI->getOperand(0).getReg()) &&
U.MI->getOperand(1).getReg() == ARM::PC) {
NewOpc = ARM::tLDRpci;
Bits = 8;
Scale = 4;
}
break;
}
if (!NewOpc)
@ -1586,6 +1596,10 @@ bool ARMConstantIslands::OptimizeThumb2Instructions(MachineFunction &MF) {
// FIXME: Check if offset is multiple of scale if scale is not 4.
if (CPEIsInRange(U.MI, UserOffset, U.CPEMI, MaxOffs, false, true)) {
U.MI->setDesc(TII->get(NewOpc));
if (NewOpc == ARM::tLDRpci)
// FIXME: Temporary workaround.
// PC is now an implicit operand.
U.MI->RemoveOperand(1);
MachineBasicBlock *MBB = U.MI->getParent();
BBSizes[MBB->getNumber()] -= 2;
AdjustBBOffsetsAfter(MBB, -2);

13
llvm/lib/Target/ARM/Thumb2SizeReduction.cpp
View File

@ -294,14 +294,11 @@ Thumb2SizeReduce::ReduceLoadStore(MachineBasicBlock &MBB, MachineInstr *MI,
HasImmOffset = true;
HasOffReg = false;
} else {
if (Entry.WideOpc == ARM::t2LDRi12) {
Opc = ARM::tLDRpci;
OpNum = 2;
}
HasImmOffset = false;
HasBaseReg = false;
HasOffReg = false;
// FIXME: Temporary workaround for a bug introduced by r121082.
// We should use t2LDRpci for loads from constantpools.
// We don't want to narrow this to tLDRpci until constant island pass
// for fear of pessimizing code.
return false;
}
break;
case ARM::t2LDRBi12: