r206963 - [ARM64] Change inline assembly constraints to be more lax, to match the behaviour of Clang/AArch64 and GCC.
Eric Christopher
echristo at gmail.com
Thu Jul 24 10:35:00 PDT 2014
Hi James,
It'd be much easier if you did it as two separate patches, the revert
and the new patch for the functionality you like. The revert is
obviously approved to go in any time :)
Thanks!
-eric
On Thu, Jul 24, 2014 at 7:28 AM, James Molloy <James.Molloy at arm.com> wrote:
> Hi Jim,
>
>
>
> Thanks for your patience on this.
>
>
>
> I’ve gone back and taken another look at this, and I believe you’re totally
> right. GCC will invisibly promote whatever you give it to 64-bits and emit
> an X-reg instruction. I agree that we want a warning here.
>
>
>
> However, I think the warning as it was pre-r206963 could be confusing for
> the user. It is not immediately obvious, for example when using the integer
> literal “0”, what the user has done wrong (here, they’d need “0L”). So the
> attached patch:
>
> · Reverts the main functionality change of r206963 (w.r.t
> modifiers).
>
> · Modifies TargetInfo to allow the modifier validation hook to
> inform Sema about a fixit hint to insert.
>
> · Implements this in AArch64TargetInfo to display a fixit.
>
>
>
> The fixit will be a cast of the asm operand to the appropriate type. I’m not
> thoroughly happy with the changes to TargetInfo – it’s quite restrictive to
> only communicate via a std::string (type to fixit-cast to). However,
> TargetInfo is in Basic and so can’t access clang::Type L
>
>
>
> Suggestions to better approaches would be appreciated!
>
>
>
> Cheers,
>
>
>
> James
>
>
>
> From: Jim Grosbach [mailto:grosbach at apple.com]
> Sent: 18 July 2014 21:16
>
>
> To: James Molloy
> Cc: cfe-commits at cs.uiuc.edu
> Subject: Re: r206963 - [ARM64] Change inline assembly constraints to be more
> lax, to match the behaviour of Clang/AArch64 and GCC.
>
>
>
> Hi James,
>
>
>
> That’s perfectly fine. It’s important to get resolved, but not super urgent.
>
>
>
> Thanks,
>
> Jim
>
>
>
> On Jul 18, 2014, at 1:00 PM, James Molloy <james.molloy at arm.com> wrote:
>
>
>
> Hi Jim,
>
> Understood - I'm on vacation until Tuesday, and I'll need to have a chat
> with others about the right way forward here. Is delaying this until Tuesday
> OK with you?
>
> Cheers,
> James
>
> ________________________________
>
> From: Jim Grosbach
> Sent: 18/07/2014 19:57
> To: James Molloy
> Cc: cfe-commits at cs.uiuc.edu
> Subject: Re: r206963 - [ARM64] Change inline assembly constraints to be more
> lax, to match the behaviour of Clang/AArch64 and GCC.
>
> Hi James,
>
> I’d like to revisit this. There were objections raised when this first went
> in that were never resolved. This warning was added because it actively
> found bugs, not for a theoretical concern. The lack of this error is now
> actively causing problems. I would very much like to see this reverted
> entirely. At the very least, please re-implement this and keep the old
> behavior, including the diagnostic, for Darwin. If other platforms want to
> be more flexible and allow potentially broken code to go through
> undiagnosed, on their own heads be it.
>
> -Jim
>
>> On Apr 23, 2014, at 3:26 AM, James Molloy <james.molloy at arm.com> wrote:
>>
>> Author: jamesm
>> Date: Wed Apr 23 05:26:19 2014
>> New Revision: 206963
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=206963&view=rev
>> Log:
>> [ARM64] Change inline assembly constraints to be more lax, to match the
>> behaviour of Clang/AArch64 and GCC.
>>
>> GCC allows sub-64bit values to use the 'r' register constraint.
>>
>> Modified:
>> cfe/trunk/lib/Basic/Targets.cpp
>> cfe/trunk/test/CodeGen/aarch64-inline-asm.c
>> cfe/trunk/test/Sema/arm64-inline-asm.c
>> cfe/trunk/test/Sema/inline-asm-validate.c
>>
>> Modified: cfe/trunk/lib/Basic/Targets.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Basic/Targets.cpp?rev=206963&r1=206962&r2=206963&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Basic/Targets.cpp (original)
>> +++ cfe/trunk/lib/Basic/Targets.cpp Wed Apr 23 05:26:19 2014
>> @@ -4643,46 +4643,37 @@ public:
>> case 'w': // Floating point and SIMD registers (V0-V31)
>> Info.setAllowsRegister();
>> return true;
>> + case 'I': // Constant that can be used with an ADD instruction
>> + case 'J': // Constant that can be used with a SUB instruction
>> + case 'K': // Constant that can be used with a 32-bit logical
>> instruction
>> + case 'L': // Constant that can be used with a 64-bit logical
>> instruction
>> + case 'M': // Constant that can be used as a 32-bit MOV immediate
>> + case 'N': // Constant that can be used as a 64-bit MOV immediate
>> + case 'Y': // Floating point constant zero
>> + case 'Z': // Integer constant zero
>> + return true;
>> + case 'Q': // A memory reference with base register and no offset
>> + Info.setAllowsMemory();
>> + return true;
>> + case 'S': // A symbolic address
>> + Info.setAllowsRegister();
>> + return true;
>> + case 'U':
>> + // Ump: A memory address suitable for ldp/stp in SI, DI, SF and DF
>> modes, whatever they may be
>> + // Utf: A memory address suitable for ldp/stp in TF mode, whatever
>> it may be
>> + // Usa: An absolute symbolic address
>> + // Ush: The high part (bits 32:12) of a pc-relative symbolic
>> address
>> + llvm_unreachable("FIXME: Unimplemented support for bizarre
>> constraints");
>> case 'z': // Zero register, wzr or xzr
>> Info.setAllowsRegister();
>> return true;
>> case 'x': // Floating point and SIMD registers (V0-V15)
>> Info.setAllowsRegister();
>> return true;
>> - case 'Q': // A memory address that is a single base register.
>> - Info.setAllowsMemory();
>> - return true;
>> }
>> return false;
>> }
>>
>> - virtual bool validateConstraintModifier(StringRef Constraint,
>> - const char Modifier,
>> - unsigned Size) const {
>> - // Strip off constraint modifiers.
>> - while (Constraint[0] == '=' || Constraint[0] == '+' || Constraint[0]
>> == '&')
>> - Constraint = Constraint.substr(1);
>> -
>> - switch (Constraint[0]) {
>> - default:
>> - return true;
>> - case 'z':
>> - case 'r': {
>> - switch (Modifier) {
>> - case 'x':
>> - case 'w':
>> - // For now assume that the person knows what they're
>> - // doing with the modifier.
>> - return true;
>> - default:
>> - // By default an 'r' constraint will be in the 'x'
>> - // registers.
>> - return (Size == 64);
>> - }
>> - }
>> - }
>> - }
>> -
>> virtual const char *getClobbers() const { return ""; }
>>
>> int getEHDataRegisterNumber(unsigned RegNo) const {
>>
>> Modified: cfe/trunk/test/CodeGen/aarch64-inline-asm.c
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/aarch64-inline-asm.c?rev=206963&r1=206962&r2=206963&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/CodeGen/aarch64-inline-asm.c (original)
>> +++ cfe/trunk/test/CodeGen/aarch64-inline-asm.c Wed Apr 23 05:26:19 2014
>> @@ -1,4 +1,5 @@
>> // RUN: %clang_cc1 -triple aarch64-none-linux-gnu -emit-llvm -o - %s |
>> FileCheck %s
>> +// RUN: %clang_cc1 -triple arm64-none-linux-gnu -emit-llvm -o - %s |
>> FileCheck %s
>>
>> // The only part clang really deals with is the lvalue/rvalue
>> // distinction on constraints. It's sufficient to emit llvm and make
>>
>> Modified: cfe/trunk/test/Sema/arm64-inline-asm.c
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/arm64-inline-asm.c?rev=206963&r1=206962&r2=206963&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Sema/arm64-inline-asm.c (original)
>> +++ cfe/trunk/test/Sema/arm64-inline-asm.c Wed Apr 23 05:26:19 2014
>> @@ -1,8 +1,9 @@
>> // RUN: %clang_cc1 -triple arm64-apple-ios7.1 -fsyntax-only -verify %s
>> +// expected-no-diagnostics
>> +
>> void foo() {
>> asm volatile("USE(%0)" :: "z"(0LL));
>> asm volatile("USE(%x0)" :: "z"(0LL));
>> asm volatile("USE(%w0)" :: "z"(0));
>>
>> - asm volatile("USE(%0)" :: "z"(0)); // expected-warning {{value size
>> does not match register size specified by the constraint and modifier}}
>> }
>>
>> Modified: cfe/trunk/test/Sema/inline-asm-validate.c
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/inline-asm-validate.c?rev=206963&r1=206962&r2=206963&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Sema/inline-asm-validate.c (original)
>> +++ cfe/trunk/test/Sema/inline-asm-validate.c Wed Apr 23 05:26:19 2014
>> @@ -1,8 +1,9 @@
>> // RUN: %clang_cc1 -triple arm64-apple-macosx10.8.0 -fsyntax-only -verify
>> %s
>> +// expected-no-diagnostics
>>
>> unsigned t, r, *p;
>>
>> int foo (void) {
>> - __asm__ __volatile__( "stxr %w[_t], %[_r], [%[_p]]" : [_t] "=&r" (t)
>> : [_p] "p" (p), [_r] "r" (r) : "memory"); // expected-warning {{value size
>> does not match register size specified by the constraint and modifier}}
>> + __asm__ __volatile__( "stxr %w[_t], %[_r], [%[_p]]" : [_t] "=&r" (t)
>> : [_p] "p" (p), [_r] "r" (r) : "memory");
>> return 1;
>> }
>>
>>
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> Registered in England & Wales, Company No: 2548782
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