[llvm-dev] By default clang does not emit trap insn

[David Blaikie via llvm-dev]

looks like experimental/work in progress support:
https://reviews.llvm.org/D62731

On Tue, May 26, 2020 at 10:39 PM kamlesh kumar via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
>
> On Wed, May 27, 2020 at 11:06 AM kamlesh kumar <kamleshbhalui at gmail.com>
> wrote:
>
>> Hi Devs,
>> going by this link https://llvm.org/docs/LangRef.html#floatenv
>> it says that floating point operation does not have side effects by
>> defaults.
>> but when compile a test case
>> i.e.
>> cat a.c
>> float foo(float a, float b)
>> {
>> return a+b;
>> }
>>
>> $clang a.c -O2 -S -emit-llvm
>> emit ir like:
>> $cat a.ll
>> ---------------------------------------
>> ; ModuleID = 'a.c'
>> source_filename = "a.c"
>> target datalayout =
>> "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
>> target triple = "x86_64-unknown-linux-gnu"
>>
>> ; Function Attrs: norecurse nounwind readnone uwtable
>> define dso_local float @foo(float %a, float %b) local_unnamed_addr #0 {
>> entry:
>>   %add = fadd float %a, %b
>>   ret float %add
>> }
>>
>> attributes #0 = { norecurse nounwind readnone uwtable
>> "correctly-rounded-divide-sqrt-fp-math"="false"
>> "disable-tail-calls"="false" "frame-pointer"="none"
>> "less-precise-fpmad"="false" "min-legal-vector-width"="0"
>> "no-infs-fp-math"="false" "no-jump-tables"="false"
>> "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
>> "no-trapping-math"="false" "stack-protector-buffer-size"="8"
>> "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87"
>> "unsafe-fp-math"="false" "use-soft-float"="false" }
>> ---------------------
>> and the setting "no-trapping-math"="false" should mean -ftrapping-math
>> but it does not and it also contradict with documentation.
>>
>> I think clang should emit this "no-trapping-math"="true" by default if it
>> goes with this assumption  https://llvm.org/docs/LangRef.html#floatenv ?
>> what is default behavior of clang -fno-trapping-math or -ftrapping-math?
>> also clang default behavior does not match gcc?
>> https://godbolt.org/z/B3YvxE
>>
>> ./kamlesh
>>
>>
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