https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121311
Bug ID: 121311
Summary: [16 Regression][gcn] Bootstrap fails in
testsuite/selftests since r16-2614-g965564eafb721f:
simplify-rtx.cc:8732: test_scalar_int_ext_ops: FAIL:
ASSERT_RTX_EQ
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
CC: ams at gcc dot gnu.org, rsandifo at gcc dot gnu.org
Target Milestone: ---
Target: gcn
Bisecting points to:
commit r16-2614-g965564eafb721f8000013a3112f1bba8d8fae32b
commit 965564eafb721f8000013a3112f1bba8d8fae32b (HEAD)
Author: Richard Sandiford
Date: Tue Jul 29 15:58:34 2025 +0100
simplify-rtx: Simplify subregs of logic ops
This patch adds a new rule for distributing lowpart subregs through
ANDs, IORs, and XORs with a constant, in cases where one of the terms
then disappears. For example:
(lowart-subreg:QI (and:HI x 0x100))
simplifies to zero and
(lowart-subreg:QI (and:HI x 0xff))
simplifies to (lowart-subreg:QI x).
This would often be handled at some point using nonzero bits. However,
the specific case I want the optimisation for is SVE predicates,
where nonzero bit tracking isn't currently an option. Specifically:
the predicate modes VNx8BI, VNx4BI and VNx2BI have the same size as
VNx16BI, but treat only every second, fourth, or eighth bit as
significant. Thus if we have:
(subreg:VNx8BI (and:VNx16BI x C))
where C is the repeating constant { 1, 0, 1, 0, ... }, then the
AND only clears bits that are made insignificant by the subreg,
and so the result is equal to (subreg:VNx8BI x). Later patches
rely on this.
gcc/
* simplify-rtx.cc (simplify_context::simplify_subreg): Distribute
lowpart subregs through AND/IOR/XOR, if doing so eliminates one
of the terms.
(test_scalar_int_ext_ops): Add some tests of the above for
integers.
* config/aarch64/aarch64.cc (aarch64_test_sve_folding): Likewise
add tests for predicate modes.
* * *
Building GCN (--enable-as-accelerator-for=x86_64-pc-linux-gnu
--target=amdgcn-amdhsa)
fails in the selftest step directly after building the actual compiler with:
LC_ALL=C GCC_COLORS=
/home/tob/projects/build-gcc-trunk-offload-amdgcn/./gcc/xgcc
-B/home/tob/projects/build-gcc-trunk-offload-amdgcn/./gcc/ -xc -nostdinc
/dev/null -S -o /dev/null
-fself-test=/home/tob/repos/gcc/gcc/testsuite/selftests
/home/tob/repos/gcc/gcc/simplify-rtx.cc:8732: test_scalar_int_ext_ops:
FAIL: ASSERT_RTX_EQ (
lowpart_subreg (smode, simplify_gen_binary (XOR, bmode, bsubreg, smask),
bmode),
lowpart_subreg (smode, gen_rtx_NOT (bmode, bsubreg), bmode))
expected: (not:SI (reg:SI 698))
actual: (subreg:SI (not:DI (subreg:DI (reg:SI 698) 0)) 0)
cc1: internal compiler error: in assert_rtx_eq_at, at selftest-rtl.cc:57
0x20fe6af internal_error(char const*, ...)
/home/tob/repos/gcc/gcc/diagnostic-global-context.cc:534
0x9eda51 fancy_abort(char const*, int, char const*)
/home/tob/repos/gcc/gcc/diagnostics/context.cc:1640
0x1105f34 selftest::assert_rtx_eq_at(selftest::location const&, char const*,
rtx_def*, rtx_def*)
/home/tob/repos/gcc/gcc/selftest-rtl.cc:57
0x1121b11 test_scalar_int_ext_ops
/home/tob/repos/gcc/gcc/simplify-rtx.cc:8732
0x11242a0 test_scalar_ops
/home/tob/repos/gcc/gcc/simplify-rtx.cc:8873
0x11242a0 selftest::simplify_rtx_cc_tests()
/home/tob/repos/gcc/gcc/simplify-rtx.cc:9455
0x1ff1072 selftest::run_tests()
/home/tob/repos/gcc/gcc/selftest-run-tests.cc:121
0x114de4a toplev::run_self_tests()
/home/tob/repos/gcc/gcc/toplev.cc:2275
