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Allow MachineCSE to coalesce trivial subregister copies the same way that it coalesces normal copies.

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Without this, MachineCSE is powerless to handle redundant operations with truncated source operands.

This required fixing the 2-addr pass to handle tied subregisters. It isn't clear what combinations of subregisters can legally be tied, but the simple case of truncated source operands is now safely handled:

     %vreg11<def> = COPY %vreg1:sub_32bit; GR32:%vreg11 GR64:%vreg1
     %vreg12<def> = COPY %vreg2:sub_32bit; GR32:%vreg12 GR64:%vreg2
     %vreg13<def,tied1> = ADD32rr %vreg11<tied0>, %vreg12<kill>, %EFLAGS<imp-def>

Test case: cse-add-with-overflow.ll.

This exposed an existing bug in
PPCInstrInfo::commuteInstruction. Thanks to Rafael for the test case:
PowerPC/crash.ll.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197465 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick
2013-12-17 04:50:45 +00:00
parent 8b81765f73
commit c4c5a1d526
6 changed files with 94 additions and 14 deletions
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lib/CodeGen/MachineCSE.cpp
+8 -3
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@@ -131,13 +131,18 @@ bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
unsigned SrcReg = DefMI->getOperand(1).getReg();
if (!TargetRegisterInfo::isVirtualRegister(SrcReg))
continue;
if (DefMI->getOperand(0).getSubReg() || DefMI->getOperand(1).getSubReg())
if (DefMI->getOperand(0).getSubReg())
continue;
if (!MRI->constrainRegClass(SrcReg, MRI->getRegClass(Reg)))
unsigned SrcSubReg = DefMI->getOperand(1).getSubReg();
const TargetRegisterClass *RC = MRI->getRegClass(Reg);
if (SrcSubReg)
RC = TRI->getMatchingSuperRegClass(MRI->getRegClass(SrcReg), RC,
SrcSubReg);
if (!MRI->constrainRegClass(SrcReg, RC))
continue;
DEBUG(dbgs() << "Coalescing: " << *DefMI);
DEBUG(dbgs() << "*** to: " << *MI);
MO.setReg(SrcReg);
MO.substVirtReg(SrcReg, SrcSubReg, *TRI);
MRI->clearKillFlags(SrcReg);
DefMI->eraseFromParent();
++NumCoalesces;