https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104957
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Tom de Vries <vr...@gcc.gnu.org>: https://gcc.gnu.org/g:f8b15e177155960017ac0c5daef8780d1127f91c commit r12-7766-gf8b15e177155960017ac0c5daef8780d1127f91c Author: Tom de Vries <tdevr...@suse.de> Date: Fri Mar 11 13:41:01 2022 +0100 [nvptx] Use .alias directive for mptx >= 6.3 Starting with ptx isa version 6.3, a ptx directive .alias is available. Use this directive to support symbol aliases, as far as possible. The alias support is off by default. It can be turned on using a switch -malias. Furthermore, for pre-sm_75, it's not effective unless the ptx version is bumped to 6.3 or higher using -mptx (given that the default for pre-sm_75 is 6.0). The alias support has the following limitations. Only function aliases are supported. Weak aliases are not supported. That is, if I disable the check in nvptx_asm_output_def_from_decls that disallows this, a weak alias is emitted and parsed by the driver. But the test gcc.dg/globalalias.c starts failing, with the behaviour matching the comment about "weird behavior of AIX's .set pseudo-op": a weak alias may resolve to different functions in different files. Aliases to weak symbols are not supported (see gcc.dg/localalias.c). This is currently not prohibited by the compiler, but with the driver link we run into: "error: Function test with .weak scope cannot be aliased". Aliases to aliases are not supported (see libgomp.c-c++-common/pr96390.c). This is currently not prohibited by the compiler, but with the driver link we run into: "Internal error: alias to unknown symbol" . Unreferenced aliases are not emitted (these can occur f.i. when inlining a call to an alias). This avoids driver link error "Internal error: reference to deleted section". When enabling malias by default, libgomp detects alias support and consequently libgomp.a will contains a few uses of .alias. This however results in aforementioned "Internal error: reference to deleted section" in many test-cases. Either there's some error with how .alias is used, or there's a driver bug. While this issue is not resolved, we keep malias off-by-default. At some point we may add support in the nvptx-tools linker for symbol aliases, and define f.i. malias=ptx and malias=ld to choose between the two in the compiler. An example of where this support is useful, is the OvO (OpenMP vs Offload) testsuite. The testsuite passes already at -O2. But at -O0, there are errors in some c++ test-cases due to missing symbol alias support. By compiling with -malias, the whole testsuite passes also at -O0. This patch causes a regression: ... -PASS: gcc.dg/pr60797.c (test for errors, line 4) +FAIL: gcc.dg/pr60797.c (test for errors, line 4) ... The test-case is skipped for effective target alias, and both without and with this patch the nvptx target is considered to not support it, so the test-case is executed. The test-case expects an error message along the lines of "alias definitions not supported in this configuration", but instead we run into: ... gcc.dg/pr60797.c:4:12: error: foo aliased to undefined symbol ... This is probably due to the fact that the nvptx backend now defines macros ASM_OUTPUT_DEF and ASM_OUTPUT_DEF_FROM_DECLS, so from the point of view of the common part of the compiler, aliases are supported. gcc/ChangeLog: 2022-03-18 Tom de Vries <tdevr...@suse.de> PR target/104957 * config/nvptx/nvptx-protos.h (nvptx_asm_output_def_from_decls): Declare. * config/nvptx/nvptx.cc (write_fn_proto_1): Don't add function marker for alias. (SET_ASM_OP, NVPTX_ASM_OUTPUT_DEF): New macro def. (nvptx_asm_output_def_from_decls): New function. * config/nvptx/nvptx.h (ASM_OUTPUT_DEF): New macro def, define to gcc_unreachable (). (ASM_OUTPUT_DEF_FROM_DECLS): New macro def, define to nvptx_asm_output_def_from_decls. * config/nvptx/nvptx.opt (malias): New opt. gcc/testsuite/ChangeLog: 2022-03-18 Tom de Vries <tdevr...@suse.de> PR target/104957 * gcc.target/nvptx/alias-1.c: New test. * gcc.target/nvptx/alias-2.c: New test. * gcc.target/nvptx/alias-3.c: New test. * gcc.target/nvptx/alias-4.c: New test. * gcc.target/nvptx/nvptx.exp (check_effective_target_runtime_ptx_isa_version_6_3): New proc.
