[llvm] r198019 - [Mips] Does not take in account 'use-soft-float' attribute's value when

Eric Christopher echristo at gmail.com
Mon Sep 29 15:15:53 PDT 2014 

On Mon, Sep 29, 2014 at 2:52 PM, reed kotler <rkotler at mips.com> wrote:
> There is a useful hidden option for testing this dual 32/16 capability in
> the Mips code generator.
>
> See MipsOS16.cpp
>
> static cl::opt<std::string> Mips32FunctionMask(
>   "mips32-function-mask",
>   cl::init(""),
>   cl::desc("Force function to be mips32"),
>   cl::Hidden);
>
> You can give it a bit mask (which is a repeatable pattern) and it will
> compile
> functions as Mip32 or Mips16 depending on how the bit is set.
>
> It's a little confusing but this Os16 was originally just an experimental
> pass I did one day
> just to toy with the idea of having a Os16 compiler option for Mips which
> compiles
> everything as Mips16 that can possibly be compiled that way without the need
> for emulation
> libraries. So it will basically compile as Mips32 any functions that do any
> floating point.
> Os16 means optimized for space using Mips16 whenever possible.
>
> I adapted this experimental pass for testing purposes to beat up this
> ability to switch
> compiling as Mips32/Mips16.
>

Nifty.

At any rate take a look at r218632.

-eric


> I have not used this is ages but basically for example, a function mask like
> "1011"
>
> will compile function 1 as mips32, function 2 as mips16 and functions 3,4 as
> Mips32
>
> I think you have to enable MipsOS16 pass to make this work.
>
> there is a little more to it than that and you can look at the code.
>
> Reed
>
> On 09/29/2014 02:29 PM, Eric Christopher wrote:
>>
>> On Mon, Sep 29, 2014 at 2:18 PM, reed kotler <rkotler at mips.com> wrote:
>>>
>>> Hi Eric,
>>>
>>> It's been a while since I worked on Mips16 floating point.
>>>
>>> Be careful though because in LLVM target independent terms, Mips16 hard
>>> float is still soft float;
>>> the difference just being which version of the fp emulation library is
>>> being
>>> used.
>>>
>> Yes, with the exception that the calling convention is soft float, but
>> mips16 hard float can still use floating point operations in
>> libraries.
>>
>>> When Mips16 hard float is on, there is a lot of difference though
>>> internally
>>> to the Mips specific targe code.
>>>
>>> Be careful in this area too because it's very complicated and we have
>>> this
>>> ability to switch between Mips16 and Mips32
>>> in the same .c file and that was tricky for me to get to work within
>>> LLVM.
>>>
>> Yes. I'm fixing up some of those issues.
>>
>>> There is one test that is failing locally for us that started to fail
>>> around
>>> the time when you were making changes
>>> and it may be unrelated to that, but it's a test for this dual 32/16 mode
>>> switching ability. I have been busy and
>>> did not look at this failure yet because I did not know about it when it
>>> first happened because we had some other
>>> issues unrelated to that in our local build bots at exactly that moment
>>> that
>>> masked the problem.
>>>
>> Likely the problem I'm fixing here. If you change the order of
>> functions in the test suite for the test I have modified you'll see a
>> failure.
>>
>>> This patch Simon made was to fix some problem we had in Mips16 build bots
>>> for test-suite and I think it's correct
>>> and for sure fixed the problem we were having. But I don't remember any
>>> of
>>> the issues.
>>
>> I'm almost certain it's not correct, but may have successfully hidden
>> the problem. I've also verified that with gcc and soft-float enabled
>> the stub is not emitted.
>>
>> Since I've verified the behavior with gcc I'm going to go ahead and
>> commit here. Let me know if you see any further problems.
>>
>> -eric
>>
>>> I will try and find some time later this week to really think about this
>>> and
>>> remember the issues.
>>>
>>> Reed
>>>
>>>
>>>
>>>
>>> On 09/29/2014 12:18 AM, Eric Christopher wrote:
>>>>
>>>> Hi Simon,
>>>>
>>>> Sorry for the thread necromancy here, but I don't think this patch is
>>>> correct.
>>>>
>>>> a) It's a bit confusing that you have bar_hf for the function with
>>>> use-soft-float set to true and vice versa for bar_sf, but
>>>> b) As far as I can recall, the stubs are only used for calling hard
>>>> float functions but the testcase currently tests that we emit it for
>>>> both.
>>>> c) The emission of the stubs should be dependent upon the subtarget
>>>> and the value of the soft-float on the function (which would be the
>>>> TM.Options.UseSoftFloat that is reset between each function, but only
>>>> in SelectionDAG or the version in the function attributes).
>>>>
>>>> With the work I've been doing plus the attached patch we'll get this
>>>> as far as I can tell correct for this - it's been a while since I've
>>>> hacked on this aspect of mips.
>>>>
>>>> -eric
>>>>
>>>>
>>>> On Wed, Dec 25, 2013 at 9:00 AM, Simon Atanasyan <simon at atanasyan.com>
>>>> wrote:
>>>>>
>>>>> Author: atanasyan
>>>>> Date: Wed Dec 25 11:00:27 2013
>>>>> New Revision: 198019
>>>>>
>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=198019&view=rev
>>>>> Log:
>>>>> [Mips] Does not take in account 'use-soft-float' attribute's value when
>>>>> consider to generate stubs for mips16 hard-float mode.
>>>>>
>>>>> The patch reviewed by Reed Kotler.
>>>>>
>>>>> Added:
>>>>>       llvm/trunk/test/CodeGen/Mips/mips16-hf-attr.ll
>>>>> Modified:
>>>>>       llvm/trunk/lib/Target/Mips/Mips16ISelLowering.cpp
>>>>>
>>>>> Modified: llvm/trunk/lib/Target/Mips/Mips16ISelLowering.cpp
>>>>> URL:
>>>>>
>>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Mips/Mips16ISelLowering.cpp?rev=198019&r1=198018&r2=198019&view=diff
>>>>>
>>>>>
>>>>> ==============================================================================
>>>>> --- llvm/trunk/lib/Target/Mips/Mips16ISelLowering.cpp (original)
>>>>> +++ llvm/trunk/lib/Target/Mips/Mips16ISelLowering.cpp Wed Dec 25
>>>>> 11:00:27
>>>>> 2013
>>>>> @@ -429,8 +429,7 @@ getOpndList(SmallVectorImpl<SDValue> &Op
>>>>>      const char* Mips16HelperFunction = 0;
>>>>>      bool NeedMips16Helper = false;
>>>>>
>>>>> -  if (getTargetMachine().Options.UseSoftFloat &&
>>>>> -      Subtarget->inMips16HardFloat()) {
>>>>> +  if (Subtarget->inMips16HardFloat()) {
>>>>>        //
>>>>>        // currently we don't have symbols tagged with the mips16 or
>>>>> mips32
>>>>>        // qualifier so we will assume that we don't know what kind it
>>>>> is.
>>>>>
>>>>> Added: llvm/trunk/test/CodeGen/Mips/mips16-hf-attr.ll
>>>>> URL:
>>>>>
>>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/Mips/mips16-hf-attr.ll?rev=198019&view=auto
>>>>>
>>>>>
>>>>> ==============================================================================
>>>>> --- llvm/trunk/test/CodeGen/Mips/mips16-hf-attr.ll (added)
>>>>> +++ llvm/trunk/test/CodeGen/Mips/mips16-hf-attr.ll Wed Dec 25 11:00:27
>>>>> 2013
>>>>> @@ -0,0 +1,45 @@
>>>>> +; Check that stubs generation for mips16 hard-float mode does not
>>>>> depend
>>>>> +; on the function 'use-soft-float' attribute's value.
>>>>> +; RUN: llc -mtriple=mipsel-linux-gnu -march=mipsel \
>>>>> +; RUN:     -mcpu=mips16 -relocation-model=pic < %s | FileCheck %s
>>>>> +
>>>>> +define void @bar_sf() #0 {
>>>>> +; CHECK: bar_sf:
>>>>> +entry:
>>>>> +  %call1 = call float @foo(float 1.000000e+00)
>>>>> +; CHECK: lw $2, %call16(foo)($3)
>>>>> +; CHECK: lw $5, %got(__mips16_call_stub_sf_1)($3)
>>>>> +  ret void
>>>>> +}
>>>>> +
>>>>> +define void @bar_hf() #1 {
>>>>> +; CHECK: bar_hf:
>>>>> +entry:
>>>>> +  %call1 = call float @foo(float 1.000000e+00)
>>>>> +; CHECK: lw $2, %call16(foo)($3)
>>>>> +; CHECK: lw $5, %got(__mips16_call_stub_sf_1)($3)
>>>>> +  ret void
>>>>> +}
>>>>> +
>>>>> +declare float @foo(float) #2
>>>>> +
>>>>> +attributes #0 = {
>>>>> +  nounwind
>>>>> +  "less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
>>>>> +  "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
>>>>> +  "no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
>>>>> +  "unsafe-fp-math"="false" "use-soft-float"="false"
>>>>> +}
>>>>> +attributes #1 = {
>>>>> +  nounwind
>>>>> +  "less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
>>>>> +  "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
>>>>> +  "no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
>>>>> +  "unsafe-fp-math"="false" "use-soft-float"="true"
>>>>> +}
>>>>> +attributes #2 = {
>>>>> +  "less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
>>>>> +  "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
>>>>> +  "no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
>>>>> +  "unsafe-fp-math"="false" "use-soft-float"="true"
>>>>> +}
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>> llvm-commits at cs.uiuc.edu
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>>>
>>>
>

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