[PATCH] [clang] dont special case the ARMv7 FPU

[Saleem Abdulrasool]

On Tue, Feb 19, 2013 at 1:59 PM, Jim Grosbach <grosbach at apple.com> wrote:
> iOS wants to default to a CPU setting of cortex-a8 when compiling for an
> arch of v7. That implies NEON. I don't know if this particular bit of code
> is necessary to make that happen properly. I suggest experimenting and
> digging a bit to see how that works.

AIUI, ARMv7 does not imply NEON.  You can have systems with a Cortex
A-8 CPU and not have a NEON FPU.  Of course, this is not something
that is desirable, but, the implication does not always hold is the
problem.  Now, special casing this for the iOS platform is perfectly
acceptable, since in that case, you know that there is a NEON FPU
available.

> In any case, changing the default of whether NEON is available for armv7
> when compiling for iOS is very much the wrong thing to do.
>
> -Jim
>
>
> On Feb 19, 2013, at 1:53 PM, Eric Christopher <echristo at gmail.com> wrote:
>
> At the very least I agree that's the wrong place to be doing that. Or it
> should be conditionalized on OS if the ios people want to do that.
>
> -eric
>
> On Tue, Feb 19, 2013 at 1:50 PM, Saleem Abdulrasool <compnerd at compnerd.org>
> wrote:
>>
>> Hi echristo, grosbach,
>>
>> ARMv7 chipsets usually are paired with a NEON FPU.  However, this is not
>> required (e.g. tegra2).  Rather than always forcing NEON as the FPU for
>> ARMv7
>> chips, honour the -mfpu flag, which already is being done.  If -mfpu is
>> not
>> specified, then let the default FPU remain selected (VFP).
>>
>> Signed-off-by: Saleem Abdulrasool <compnerd at compnerd.org>
>>
>>
>> http://llvm-reviews.chandlerc.com/D425
>>
>> Files:
>>   lib/Driver/Tools.cpp
>>
>> Index: lib/Driver/Tools.cpp
>> ===================================================================
>> --- lib/Driver/Tools.cpp
>> +++ lib/Driver/Tools.cpp
>> @@ -5494,10 +5494,6 @@
>>      CmdArgs.push_back("-mppc64");
>>      CmdArgs.push_back("-many");
>>    } else if (getToolChain().getArch() == llvm::Triple::arm) {
>> -    StringRef MArch = getToolChain().getArchName();
>> -    if (MArch == "armv7" || MArch == "armv7a" || MArch == "armv7-a")
>> -      CmdArgs.push_back("-mfpu=neon");
>> -
>>      StringRef ARMFloatABI = getARMFloatABI(getToolChain().getDriver(),
>> Args,
>>                                             getToolChain().getTriple());
>>      CmdArgs.push_back(Args.MakeArgString("-mfloat-abi=" + ARMFloatABI));
>
>
>



-- 
Saleem Abdulrasool
compnerd (at) compnerd (dot) org