[gcc] Prefer bsl/bit/bif for copysignf. (backport GCC-8)

[direc85]

This (slightly modified) patch supposedly fixes the compiler segfault @llewelld ran into while updating Gecko from ESR 78 to ESR 91:

47:04.13   cargo:warning=during RTL pass: expand
47:04.13   cargo:warning=src/glsl.h: In function ‘glsl::vec2_scalar
           glsl::sign(glsl::vec2_scalar)’:
47:04.13   cargo:warning=src/glsl.h:662:39: internal compiler error:
           Segmentation fault
47:04.13   cargo:warning= float sign(float a) { return copysignf(1.0f, a); }
47:04.13   cargo:warning=                              ~~~~~~~~~^~~~~~~~~
47:04.13   cargo:warning=Please submit a full bug report,
47:04.13   cargo:warning=with preprocessed source if appropriate.
47:04.14   cargo:warning=See  for instructions.
47:04.14   exit status: 1

I haven't been able to compile nor test this patch in Platform SDK, but with minor tweaks (two changes for Changelog and a one-line add for aarch64.md) the patch applies at least. As such, I wish to someone who is more familiar with this process pick this up and build/test it further.

The original bug I found was: Bug 90075 - [7/8 Regression] [AArch64] ICE during RTL pass when member of union passed to copysignf (also contains code to reproduce the issue - untested my be though).

The unmodified patch can be downloaded here (or from the bug link by following the gcc-8 backport links).

[mlehtima]

You need to run the precheckin.sh script to sync the cross-gcc spec files with gcc.spec.

[Thaodan]

Please smash the two commits

[direc85]

precheckin.sh script ran and commits squashed.

[Thaodan]

LGTM

[direc85]

We still don't know if this patch actually fixes the problem flypig is facing with gecko build. I would have built this myself, but it looks like not all cross-aarch64 dependencies for GCC are available for i486 built target. The cross-i486 dependencies are available, and I can compile that one, but it doesn't help here. Perhaps OBS helps us out here.

[Thaodan]

Did you install the cross-* packages into the tooling? Which cross-aarch64 dependencies are missing?

[rainemak]

@direc85 this is neat! As discussed earlier today, let's do not merge quite yet.

Quote from @llewelld from IRC meeting:

As it happens the latest changes built for aarch64 on OBS last night, so I can now test this on the gecko source. I don't think it makes sense to merge it before that.

[llewelld]

I was just able to test this new version, and it does seem to fix the issue I was experiencing. Here's the error output from before:

In file included from src/glsl.h:7,
                 from src/gl.cc:92:
src/vector_type.h: In instantiation of ‘static T glsl::Unaligned<T>::load(const P*) [with P = glsl::VectorType<float, 16>; T = glsl::vec4]’:
src/vector_type.h:532:28:   required from ‘T glsl::unaligned_load(const P*) [with T = glsl::vec4; P = glsl::VectorType<float, 16>]’
src/vector_type.h:543:27:   required from ‘D glsl::bit_cast(const S&) [with D = glsl::vec4; S = glsl::VectorType<float, 16>]’
src/blend.h:53:41:   required from here
src/vector_type.h:503:11: warning: ‘void* memcpy(void*, const void*, size_t)’ writing to an object of type ‘struct glsl::vec4’ with no trivial copy-assignment; use copy-assignment or copy-initialization instead [-Wclass-memaccess]
     memcpy(&v, p, sizeof(v));
     ~~~~~~^~~~~~~~~~~~~~~~~~
In file included from src/gl.cc:92:
src/glsl.h:1796:8: note: ‘struct glsl::vec4’ declared here
 struct vec4 {
        ^~~~
during RTL pass: expand
src/glsl.h: In function ‘glsl::vec2_scalar glsl::sign(glsl::vec2_scalar)’:
src/glsl.h:662:39: internal compiler error: Segmentation fault
 float sign(float a) { return copysignf(1.0f, a); }
                              ~~~~~~~~~^~~~~~~~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://git.sailfishos.org/> for instructions.

And this is what I get now (no error!):

In file included from src/glsl.h:7,
                 from src/gl.cc:92:
src/vector_type.h: In instantiation of ‘static T glsl::Unaligned<T>::load(const P*) [with P = glsl::VectorType<float, 16>; T = glsl::vec4]’:
src/vector_type.h:532:28:   required from ‘T glsl::unaligned_load(const P*) [with T = glsl::vec4; P = glsl::VectorType<float, 16>]’
src/vector_type.h:543:27:   required from ‘D glsl::bit_cast(const S&) [with D = glsl::vec4; S = glsl::VectorType<float, 16>]’
src/blend.h:53:41:   required from here
src/vector_type.h:503:11: warning: ‘void* memcpy(void*, const void*, size_t)’ writing to an object of type ‘struct glsl::vec4’ with no trivial copy-assignment; use copy-assignment or copy-initialization instead [-Wclass-memaccess]
     memcpy(&v, p, sizeof(v));
     ~~~~~~^~~~~~~~~~~~~~~~~~
In file included from src/gl.cc:92:
src/glsl.h:1796:8: note: ‘struct glsl::vec4’ declared here
 struct vec4 {
        ^~~~

Great work @direc85!

[llewelld]

This fixes the issue I was experiencing. Thanks @direc85!

[mlehtima]

I will make a full devel test build with these changs to make sure nothing breaks. If that is ok then I will approve this.