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

[Hans Wennborg via llvm-commits]

Merged in r311461. Thanks!

On Mon, Aug 21, 2017 at 9:36 PM, Saleem Abdulrasool
<compnerd at compnerd.org> wrote:
> Indeed I did :-).  It is very targeted and trivial and I believe it to be a
> very low-risk fix for a nasty codegen issue.
>
> On Mon, Aug 21, 2017 at 4:57 PM, Hans Wennborg <hans at chromium.org> wrote:
>>
>> 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>
>> > +
>> >
>> >
>> > _______________________________________________
>> > llvm-commits mailing list
>> > llvm-commits at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
>
>
>
> --
> Saleem Abdulrasool
> compnerd (at) compnerd (dot) org