On 1/12/25 11:47 AM, Jakub Jelinek wrote:
Hi!
As mentioned in the second PR, using table names like
crc_table_for_crc_8_polynomial_0x12
in the user namespace is wrong, user could have defined such variables
in their code and as can be seen on the last testcase, then it just
misbehaves.
At minimum such names should start with 2 underscores, moving it into
implementation namespace, and if possible have some dot or dollar in the
name if target supports it.
I think assemble_crc_table right now always emits tables a local variables,
I really don't see what would be setting TREE_PUBLIC flag on
IDENTIFIER_NODEs.
It might be nice to share the tables between TUs in the same binary or
shared library, but it in that case should have hidden visibility if
possible, so that it isn't exported from the libraries or binaries, we don't
want the optimization to affect set of exported symbols from libraries.
And, as can be seen in the first PR, building gen_rtx_SYMBOL_REF by hand
is certainly unexpected on some targets, e.g. those which use
-fsection-anchors, so we should instead use DECL_RTL of the VAR_DECL.
For that we'd need to look it up if we haven't emitted it already, while
IDENTIFIER_NODEs can be looked up easily, I guess for the VAR_DECLs we'd
need custom hash table.
Now, all of the above (except sharing between multiple TUs) is already
implemented in output_constant_def, so I think it is much better to just
use that function.
And, if we want to share it between multiple TUs, we could extend the
SHF_MERGE usage in gcc, currently we only use it for constant pool
entries with same size as alignment, from 1 to 32 bytes, using .rodata.cstN
sections. We could just use say .rodata.cstM.N sections where M would be
alignment and N would be the entity size. We could use that for all
constant pool entries say up to 2048 bytes.
Though, as the current code doesn't share between multiple TUs, I think it
can be done incrementally (either still for GCC 15, or GCC 16+).
Bootstrapped/regtested on {x86_64,i686,aarch64,powerpc64le,s390x}-linux, on
aarch64 it also fixes
-FAIL: crypto/rsa
-FAIL: hash
ok for trunk?
2025-01-12 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/117997
PR middle-end/118415
* expr.cc (assemble_crc_table): Make static, remove id argument,
use output_constant_def. Emit note if -fdump-rtl-expand-details
about which table has been emitted.
(generate_crc_table): Make static, adjust assemble_crc_table
caller, call it always.
(calculate_table_based_CRC): Make static.
* internal-fn.cc (expand_crc_optab_fn): Emit note if
-fdump-rtl-expand-details about using optab for crc. Formatting fix.
* gcc.dg/crc-builtin-target32.c: Add -fdump-rtl-expand-details
as dg-additional-options. Scan expand dump rather than assembly,
adjust the regexps.
* gcc.dg/crc-builtin-target64.c: Likewise.
* gcc.dg/crc-builtin-rev-target32.c: Likewise.
* gcc.dg/crc-builtin-rev-target64.c: Likewise.
* gcc.dg/pr117997.c: New test.
* gcc.dg/pr118415.c: New test.
I went ahead and commited/pushed this to the trunk. Thanks again Jakub.
jeff
