[llvm] r311061 - ARM: mark CPSR as clobbered for Windows VLAs

[Hans Wennborg via llvm-commits]

I think you asked on IRC for this to be merged?

On Wed, Aug 16, 2017 at 7:42 PM, Saleem Abdulrasool via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: compnerd
> Date: Wed Aug 16 19:42:24 2017
> New Revision: 311061
>
> URL: http://llvm.org/viewvc/llvm-project?rev=311061&view=rev
> Log:
> ARM: mark CPSR as clobbered for Windows VLAs
>
> When lowering a VLA, we emit a __chstk call.  However, this call can
> internally clobber CPSR.  We did not mark this register as an ImpDef,
> which could potentially allow a comparison to be hoisted above the call
> to `__chkstk`.  In such a case, the CPSR could be clobbered, and the
> check invalidated.  When the support was initially added, it seemed that
> the call would take care of preventing CPSR from being clobbered, but
> this is not the case.  Mark the register as clobbered to fix a possible
> state corruption.
>
> Added:
>     llvm/trunk/test/CodeGen/ARM/Windows/vla-cpsr.ll
> Modified:
>     llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
>
> Modified: llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp?rev=311061&r1=311060&r2=311061&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp (original)
> +++ llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp Wed Aug 16 19:42:24 2017
> @@ -8790,6 +8790,8 @@ ARMTargetLowering::EmitLowered__chkstk(M
>          .addReg(ARM::R4, RegState::Implicit | RegState::Kill)
>          .addReg(ARM::R4, RegState::Implicit | RegState::Define)
>          .addReg(ARM::R12,
> +                RegState::Implicit | RegState::Define | RegState::Dead)
> +        .addReg(ARM::CPSR,
>                  RegState::Implicit | RegState::Define | RegState::Dead);
>      break;
>    case CodeModel::Large: {
> @@ -8804,6 +8806,8 @@ ARMTargetLowering::EmitLowered__chkstk(M
>          .addReg(ARM::R4, RegState::Implicit | RegState::Kill)
>          .addReg(ARM::R4, RegState::Implicit | RegState::Define)
>          .addReg(ARM::R12,
> +                RegState::Implicit | RegState::Define | RegState::Dead)
> +        .addReg(ARM::CPSR,
>                  RegState::Implicit | RegState::Define | RegState::Dead);
>      break;
>    }
>
> Added: llvm/trunk/test/CodeGen/ARM/Windows/vla-cpsr.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/Windows/vla-cpsr.ll?rev=311061&view=auto
> ==============================================================================
> --- llvm/trunk/test/CodeGen/ARM/Windows/vla-cpsr.ll (added)
> +++ llvm/trunk/test/CodeGen/ARM/Windows/vla-cpsr.ll Wed Aug 16 19:42:24 2017
> @@ -0,0 +1,13 @@
> +; RUN: llc -mtriple thumbv7-windows-itanium -filetype asm -o /dev/null %s -print-machineinstrs=expand-isel-pseudos 2>&1 | FileCheck %s
> +
> +declare arm_aapcs_vfpcc void @g(i8*) local_unnamed_addr
> +
> +define arm_aapcs_vfpcc void @f(i32 %i) local_unnamed_addr {
> +entry:
> +  %vla = alloca i8, i32 %i, align 1
> +  call arm_aapcs_vfpcc void @g(i8* nonnull %vla)
> +  ret void
> +}
> +
> +; CHECK: tBL pred:14, pred:%noreg, <es:__chkstk>, %LR<imp-def>, %SP<imp-use>, %R4<imp-use,kill>, %R4<imp-def>, %R12<imp-def,dead>, %CPSR<imp-def,dead>
> +
>
>
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