[PATCH] switch ARM modes in inline asm

[Greg Fitzgerald]

Hi David,

Thanks for the review.  No, this patch only goes as far as correcting
the broken machine code in the Thumb->ARM->Thumb case.  It assumes the
inline assembly is responsible for restoring the mode.  But since the
inline assembly doesn't know what mode the C++ was compiled in, I
think my assumption is unreasonable.  I'll send an updated patch that
adds a setFeatureBits() method to the SubtargetInfo class and uses it
to restore the mode.

Thanks,
Greg


On Fri, Nov 22, 2013 at 2:53 PM, David Peixotto <dpeixott at codeaurora.org> wrote:
> Will this patch properly restore the mode when returning from the inlineasm? Say we have this function
>
> foo() {
>   // assembling in arm mode
>   __asm__(".thumb")
>   // are we still assembling in arm mode?
> }
>
> Will it make sure that the non-inline asm portions of the function are all compilied in arm mode?
>
>> -----Original Message-----
>> From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-
>> bounces at cs.uiuc.edu] On Behalf Of Greg Fitzgerald
>> Sent: Friday, November 22, 2013 12:37 PM
>> To: grosbach at apple.com; amara.emerson at arm.com; garious at gmail.com;
>> t.p.northover at gmail.com
>> Cc: llvm-commits at cs.uiuc.edu
>> Subject: [PATCH] switch ARM modes in inline asm
>>
>> Hi grosbach, aemerson,
>>
>> Fix inline assembly that switches between ARM and Thumb modes
>>
>> This patch assumes the inline assembly is responsible for restoring the
>> mode.
>>
>>
>> http://llvm-reviews.chandlerc.com/D2255
>>
>> Files:
>>   lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
>>   test/CodeGen/ARM/2013-11-22-inline-asm-switch-mode.ll
>>
>> Index: lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
>> ===================================================================
>> --- lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
>> +++ lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
>> @@ -33,6 +33,7 @@
>>  #include "llvm/Support/TargetRegistry.h"
>>  #include "llvm/Support/raw_ostream.h"
>>  #include "llvm/Target/TargetMachine.h"
>> +#include "llvm/Target/TargetSubtargetInfo.h"
>>  using namespace llvm;
>>
>>  namespace {
>> @@ -114,14 +115,11 @@
>>                                                    OutContext,
>> OutStreamer,
>>                                                    *MAI));
>>
>> -  // FIXME: It would be nice if we can avoid createing a new instance of
>> -  // MCSubtargetInfo here given TargetSubtargetInfo is available.
>> However,
>> -  // we have to watch out for asm directives which can change subtarget
>> -  // state. e.g. .code 16, .code 32.
>> -  OwningPtr<MCSubtargetInfo>
>> -    STI(TM.getTarget().createMCSubtargetInfo(TM.getTargetTriple(),
>> -                                             TM.getTargetCPU(),
>> -
>> TM.getTargetFeatureString()));
>> +  // Reuse the existing Subtarget, because the AsmParser will  //
>> + modify it.  For example, when switching between ARM and  // Thumb
>> + mode.
>> +  const MCSubtargetInfo* STC = TM.getSubtargetImpl();
>> +  MCSubtargetInfo* STI = const_cast<MCSubtargetInfo*>(STC);
>>    OwningPtr<MCTargetAsmParser>
>>      TAP(TM.getTarget().createMCAsmParser(*STI, *Parser, *MII));
>>    if (!TAP)
>> Index: test/CodeGen/ARM/2013-11-22-inline-asm-switch-mode.ll
>> ===================================================================
>> --- /dev/null
>> +++ test/CodeGen/ARM/2013-11-22-inline-asm-switch-mode.ll
>> @@ -0,0 +1,13 @@
>> +;RUN:  llc -mtriple=thumbv7-linux-gnueabi -filetype=obj < %s |
>> +llvm-objdump -arch=thumb -d - | FileCheck %s
>> +
>> +target triple = "thumbv7--linux-gnueabi"
>> +
>> +define hidden void @bah(i8* %start) #0 align 2 {
>> +  %1 = ptrtoint i8* %start to i32
>> +  %2 = tail call i32 asm sideeffect "@ Enter ARM Mode  \0A\09adr r3, 1f
>> +\0A\09bx  r3 \0A\09.align 2 \0A\09.code 32 \0A1:  push {r7} \0A\09mov
>> +r7, $4 \0A\09svc 0x0 \0A
>> +  ret void
>> +}
>> +; CHECK: $a
>> +; CHECK-NEXT: 04 70
>> +; CHECK-NEXT: 2d e5
>> +
>
>
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