On Tuesday, May 8, 2018 1:23:32 AM PDT Eero Tamminen wrote:
> Hi,
>
> On 08.05.2018 06:45, Matt Turner wrote:
> > On Mon, May 7, 2018 at 8:02 PM, Brian Paul <bri...@vmware.com> wrote:
> >>
> >> I don't know when this started happening (I'll try bisecting tomorrow) but
> >> we're seeing a crash in ast_type_qualifier::validate_in_qualifier() in -O3
> >> builds with gcc 5.4.0 on Ubuntu 16.04.
> >>
> >> Specifically, at ast_type.cpp:654:
> >>
> >> if ((this->flags.i & ~valid_in_mask.flags.i) != 0) {
> >>
> >> It seems to be the ~ operator/function which is implemented with an SSE
> >> pxor
> >> instruction.
> >>
> >> I found that this patch avoids the issue:
> >>
> >> diff --git a/src/compiler/glsl/ast.h b/src/compiler/glsl/ast.h
> >> index a1ec0d5..2e518ce 100644
> >> --- a/src/compiler/glsl/ast.h
> >> +++ b/src/compiler/glsl/ast.h
> >> @@ -474,7 +474,7 @@ enum {
> >>
> >> struct ast_type_qualifier {
> >> DECLARE_RALLOC_CXX_OPERATORS(ast_type_qualifier);
> >> - DECLARE_BITSET_T(bitset_t, 128);
> >> + DECLARE_BITSET_T(bitset_t, 96);
> >>
> >> union flags {
> >> struct {
> >>
> >> This probably prevents use of xmm instructions, but I haven't inspected the
> >> code.
> >>
> >> Is anyone else seeing this?
> >
> > Yes, it's https://bugs.freedesktop.org/show_bug.cgi?id=105497
> >
> > I was surprised that we decided it's not worth working around.
>
> By making above part perform worse for everybody using -O3, or by
> disabling vectorization optimization (enabled by -O3) just for
> the buggy GCC version?
>
> (If that GCC version gets it wrong in this place, it may get it
> wrong also elsewhere, so better turn that particular -O3 optimization
> off completely.)
>
> Is there an upstream GCC bug report about that, which would tell
> which GCC versions are affected?
>
>
> - EeroI wouldn't worry about performance here, the AST code is basically never the hot path (even without shader cache, and now it's glacial). I was honestly surprised to see it start using xmm intrinsics. --Ken
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