gcc-14 bug compiling test/arm/neon/ext.cpp on x86

[Blarse]

When compiling simde with gcc 14.2.1 on i586 I get the following error:

[1561/4004] Compiling C++ object test/arm/neon/ext-emul-cpp.p/meson-generated_.._ext.cpp.o
FAILED: test/arm/neon/ext-emul-cpp.p/meson-generated_.._ext.cpp.o 
c++ -Itest/arm/neon/ext-emul-cpp.p -Itest/arm/neon -I../test/arm/neon -I. -I.. -fdiagnostics-color=always -D_GLIBCXX_ASSERTIONS=1 -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -O2 -g -pipe -frecord-gcc-switches -Wall -g -O2 -flto=auto -march=i586 -mtune=generic -fopenmp-simd -DSIMDE_CONSTRAINED_COMPILATION -DSIMDE_ENABLE_OPENMP -Wno-psabi -DSIMDE_TEST_BARE -DSIMDE_NO_NATIVE -ffloat-store -MD -MQ test/arm/neon/ext-emul-cpp.p/meson-generated_.._ext.cpp.o -MF test/arm/neon/ext-emul-cpp.p/meson-generated_.._ext.cpp.o.d -o test/arm/neon/ext-emul-cpp.p/meson-generated_.._ext.cpp.o -c test/arm/neon/ext.cpp
during GIMPLE pass: local-fnsummary
In file included from test/arm/neon/ext.cpp:2235:
../test/arm/neon/test-neon-footer.h: In function ‘simde_vext_p64’:
../test/arm/neon/test-neon-footer.h:17:3: internal compiler error: in predicate_for_phi_result, at ipa-fnsummary.cc:2447
   17 |   }
      |   ^
0x8fcfced internal_error(char const*, ...)
	???:0
0x8fcfdc2 fancy_abort(char const*, int, char const*)
	???:0
0x92f057c compute_fn_summary(cgraph_node*, bool)
	???:0
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.

The bug occurs only with -O2 or -O3 in function simde_vext_p64 specifically in simde/arm/neon/ext.h:967, when assigning destination vector values:

r_.values[i] = (src < (sizeof(r_.values) / sizeof(r_.values[0]))) ? a_.values[src] : b_.values[src & 0];

Simply reversing the condition fixes the issue:

r_.values[i] = (src >= (sizeof(r_.values) / sizeof(r_.values[0]))) ? b_.values[src & 0] : a_.values[src];

[mr-c]

Thank you @Blarse for the report. Did you file an issue in the GCC bug tracker?

[Blarse]

Thank you @Blarse for the report. Did you file an issue in the GCC bug tracker?

Not yet actually, as I found this with our ALT Linux gcc ("i586-alt-linux-gcc (GCC) 14.2.1 20241028 (ALT Sisyphus 14.2.1-alt1)") and still wasn't able to test if this bug occurs on other systems. If you have an i586 system with gcc-14 at hand, I would appreciate it if you could confirm this error.

I'm also trying to create a small and independent from simde reproducer.

If you think it's better to report this right now without additional analysis, then I'll do it.

[Blarse]

I've written a minimal reproducer.
Also I was able to reproduce this bug in debian experimental container with gcc (Debian 14.2.0-11) 14.2.0

#include "stdint.h"
#include "stddef.h"

typedef uint64_t poly64x1 __attribute__((__vector_size__(8)));

poly64x1 vext_p64(poly64x1 a, poly64x1 b, const int n)
{
  poly64x1 r = a;
  size_t src = ((size_t) (n));
  r[0] = (src < 1) ? a[src] : b[0];
  return r;
}

$ gcc -O2 -c ./reproducer.c 
during GIMPLE pass: local-fnsummary
./reproducer.c: In function 'vext_p64':
./reproducer.c:12:1: internal compiler error: in predicate_for_phi_result, at ipa-fnsummary.cc:2447
   12 | }
      | ^
0x9133008 internal_error(char const*, ...)
	???:0
0x91330d2 fancy_abort(char const*, int, char const*)
	???:0
0x9291277 compute_fn_summary(cgraph_node*, bool)
	???:0
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-14/README.Bugs> for instructions.

$ gcc -O1 -c ./reproducer.c 
during GIMPLE pass: uncprop
./reproducer.c: In function 'vext_p64':
./reproducer.c:6:10: internal compiler error: in promote_ssa_mode, at explow.cc:923
    6 | poly64x1 vext_p64(poly64x1 a, poly64x1 b, const int n)
      |          ^~~~~~~~
0x9133008 internal_error(char const*, ...)
	???:0
0x91330d2 fancy_abort(char const*, int, char const*)
	???:0
0x93bf7d9 gimple_can_coalesce_p(tree_node*, tree_node*)
	???:0
0x944fe9d uncprop_dom_walker::before_dom_children(basic_block_def*)
	???:0
0x958ed71 dom_walker::walk(basic_block_def*)
	???:0
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-14/README.Bugs> for instructions.

Now I will create an issue in the GCC bug tracker.

[mr-c]

That's great, thank you @Blarse . We can add the GCC bug number to https://github.com/simd-everywhere/simde/wiki/Compiler-Bugs