[PATCH] propagate IR-level fast-math-flags to DAG nodes, disabled by default

[Sanjay Patel]

Hi Nick,

The reciprocal fix is in at r241826. Please let me know when you find
another failure. Thanks!

On Mon, Jun 22, 2015 at 3:43 PM, Nick Lewycky <nlewycky at google.com> wrote:

> On 22 June 2015 at 14:09, Sanjay Patel <spatel at rotateright.com> wrote:
>
>> Thanks, Nick.
>>
>> This is the same bug (convert repeated divisions by the same divisor to
>> multiplication by the reciprocal) that should be solved by D9893 (
>> http://reviews.llvm.org/D9893 ). After I apply that patch, the output
>> asm looks correct to me.
>>
>
> OK! Let me know once that lands and I'll re-test it. There were a lot of
> failures, so there may be something more left after this particular problem
> is resolved.
>
>
>>
>> On Fri, Jun 19, 2015 at 5:53 PM, Nick Lewycky <nlewycky at google.com>
>> wrote:
>>
>>> On 17 June 2015 at 13:57, Sanjay Patel <spatel at rotateright.com> wrote:
>>>
>>>>
>>>>
>>>> On Wed, Jun 17, 2015 at 12:59 AM, Nick Lewycky <nicholas at mxc.ca> wrote:
>>>>
>>>>> Sanjay Patel wrote:
>>>>>
>>>>>> Please let me know if I can still take you up on this offer:
>>>>>> "Could you add FMF under a flag and then let me test it before
>>>>>> turning it on? I can test for compiler crashes in 24 hours, or for
>>>>>> miscompiles over a weekend."
>>>>>>
>>>>>
>>>>> Right! Yes, I can do that.
>>>>>
>>>>
>>>> Great! Let me know when you see bugs crawling out from under the rug. :)
>>>>
>>>
>>> Just finished the first creduce.
>>>
>>> Testcase:
>>>
>>> int a, b, c;
>>> void fn1() {
>>>   b = c / (1.0 + c);
>>>   a = 1 / (1.0 + c);
>>> }
>>>
>>> Build with "clang -O2 -mllvm -enable-fmf-dag -ffast-math" to get
>>>
>>>  fatal error: error in backend: Cannot select: 0x2a8a760: f64 =
>>>       ConstantFP<1.000000e+00> [ID=7]
>>> In function: _Z3fn1v
>>>
>>> and here it is as .ll:
>>>
>>> target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>>> target triple = "x86_64-grtev4-linux-gnu"
>>>
>>> @a = global i32 0, align 4
>>> @b = global i32 0, align 4
>>> @c = global i32 0, align 4
>>>
>>> ; Function Attrs: nounwind uwtable
>>> define void @_Z3fn1v() #0 {
>>>   %1 = load i32, i32* @c, align 4, !tbaa !1
>>>   %2 = sitofp i32 %1 to double
>>>   %3 = fadd fast double %2, 1.000000e+00
>>>   %4 = fdiv fast double %2, %3
>>>   %5 = fptosi double %4 to i32
>>>   store i32 %5, i32* @b, align 4, !tbaa !1
>>>   %6 = fdiv fast double 1.000000e+00, %3
>>>   %7 = fptosi double %6 to i32
>>>   store i32 %7, i32* @a, align 4, !tbaa !1
>>>   ret void
>>> }
>>>
>>> attributes #0 = { nounwind uwtable "disable-tail-calls"="false"
>>> "less-precise-fpmad"="false" "no-frame-pointer-elim"="false"
>>> "no-infs-fp-math"="true" "no-nans-fp-math"="true"
>>> "stack-protector-buffer-size"="8" "target-cpu"="x86-64"
>>> "target-features"="+sse,+sse2" "unsafe-fp-math"="true"
>>> "use-soft-float"="false" }
>>>
>>> !llvm.ident = !{!0}
>>>
>>> !0 = !{!"clang version google3-trunk (trunk r240125)"}
>>> !1 = !{!2, !2, i64 0}
>>> !2 = !{!"int", !3, i64 0}
>>> !3 = !{!"omnipotent char", !4, i64 0}
>>> !4 = !{!"Simple C/C++ TBAA"}
>>>
>>>
>>
>
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