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[Register Coalescer] Fix wrong live-range information with rematerialization.

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When rematerializing an instruction that defines a super register that would be
used by a physical subregisters we use the related physical super register for
the definition.
To keep the live-range information accurate, all the defined subregisters must be
marked as dead def, otherwise the register allocation may miss some
interferences.

Working on a reduced test-case!

<rdar://problem/16582185>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206060 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Quentin Colombet 2014-04-11 19:45:07 +00:00
parent 6e6126ac4c
commit 441d6d505b
1 changed files with 21 additions and 0 deletions
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21
lib/CodeGen/RegisterCoalescer.cpp
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@ -844,6 +844,27 @@ bool RegisterCoalescer::reMaterializeTrivialDef(CoalescerPair &CP,
true /*IsDef*/, true /*IsDef*/,
true /*IsImp*/, true /*IsImp*/,
false /*IsKill*/)); false /*IsKill*/));
// Record small dead def live-ranges for all the subregisters
// of the destination register.
// Otherwise, variables that live through may miss some
// interferences, thus creating invalid allocation.
// E.g., i386 code:
// vreg1 = somedef ; vreg1 GR8
// vreg2 = remat ; vreg2 GR32
// CL = COPY vreg2.sub_8bit
// = somedef vreg1 ; vreg1 GR8
// =>
// vreg1 = somedef ; vreg1 GR8
// ECX<def, dead> = remat ; CL<imp-def>
// = somedef vreg1 ; vreg1 GR8
// vreg1 will see the inteferences with CL but not with CH since
// no live-ranges would have been created for ECX.
// Fix that!
SlotIndex NewMIIdx = LIS->getInstructionIndex(NewMI);
for (MCRegUnitIterator Units(NewMI->getOperand(0).getReg(), TRI);
Units.isValid(); ++Units)
if (LiveRange *LR = LIS->getCachedRegUnit(*Units))
LR->createDeadDef(NewMIIdx.getRegSlot(), LIS->getVNInfoAllocator());
} }
if (NewMI->getOperand(0).getSubReg()) if (NewMI->getOperand(0).getSubReg())