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

[Nick Lewycky]

On 9 July 2015 at 15:27, Sanjay Patel <spatel at rotateright.com> wrote:

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

Thank you! I tested it and found exactly nothing wrong. Hopefully I didn't
goof the testing, but I think it's time to flip the flag to true, then wait
a few days before removing the flag entirely.

Note however, that we still have problems with PR24141 which is related to
unsafe fp math, but doesn't change with the -enable-fmf-dag flag.

Nick

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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