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Richard Sandiford 6cedf5d8e2 predcom: Fix invalid store-store commoning [PR93434]
predcom has the following code to stop one rogue load from
interfering with other store-load opportunities:

      /* If A is read and B write or vice versa and there is unsuitable
	 dependence, instead of merging both components into a component
	 that will certainly not pass suitable_component_p, just put the
	 read into bad component, perhaps at least the write together with
	 all the other data refs in it's component will be optimizable.  */

But when store-store commoning was added later, this had the effect
of ignoring loads that occur between two candidate stores.

There is code further up to handle loads and stores with unknown
dependences:

      /* Don't do store elimination if there is any unknown dependence for
	 any store data reference.  */
      if ((DR_IS_WRITE (dra) || DR_IS_WRITE (drb))
	  && (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know
	      || DDR_NUM_DIST_VECTS (ddr) == 0))
	eliminate_store_p = false;

But the store-load code above skips loads for *known* dependences
if (a) the load has already been marked "bad" or (b) the data-ref
machinery knows the dependence distance, but determine_offsets
can't handle the combination.

(a) happens to be the problem in the testcase, but a different
sequence could have given (b) instead.  We have writes to individual
fields of a structure and reads from the whole structure.  Since
determine_offsets requires the types to be the same, it returns false
for each such read/write combination.

This patch records which components have had loads removed and
prevents store-store commoning for them.  It's a bit too pessimistic,
since there shouldn't be a problem if a "bad" load dominates all stores
in a component.  But (a) we can't AFAIK use pcom_stmt_dominates_stmt_p
here and (b) the handling for that case would probably need to be
removed again if we handled more exotic cases in future.

2020-01-28  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR tree-optimization/93434
	* tree-predcom.c (split_data_refs_to_components): Record which
	components have had aliasing loads removed.  Prevent store-store
	commoning for all such components.

gcc/testsuite/
	PR tree-optimization/93434
	* gcc.c-torture/execute/pr93434.c: New test.
2020-01-28 10:47:43 +00:00
config gcc: Add new configure options to allow static libraries to be selected 2020-01-27 22:02:35 +00:00
contrib contrib: Change 'remote' for personal branches and add branch creation script 2020-01-24 14:38:16 +00:00
fixincludes Fix missing SCNuMAX defines in inttypes.h on hpux11.[01]* 2020-01-25 12:20:24 -05:00
gcc predcom: Fix invalid store-store commoning [PR93434] 2020-01-28 10:47:43 +00:00
gnattools PR81878: fix --disable-bootstrap --enable-languages=ada 2018-11-20 00:07:47 +00:00
gotools libgo: update to Go1.14beta1 2020-01-21 23:53:22 -08:00
include OpenACC 'acc_get_property' cleanup 2020-01-10 23:24:36 +01:00
INSTALL
intl iconv.m4 (AM_ICONV_LINK): Don't overwrite CPPFLAGS. 2018-11-07 15:41:21 -07:00
libada Add `--with-toolexeclibdir=' configuration option 2020-01-24 11:24:25 +00:00
libatomic Add `--with-toolexeclibdir=' configuration option 2020-01-24 11:24:25 +00:00
libbacktrace Update copyright years. 2020-01-01 12:51:42 +01:00
libcc1 init.c (build_new): Add location_t parameter and use it throughout. 2020-01-07 17:58:18 +00:00
libcpp gcc: Add new configure options to allow static libraries to be selected 2020-01-27 22:02:35 +00:00
libdecnumber Update copyright years. 2020-01-01 12:51:42 +01:00
libffi Add `--with-toolexeclibdir=' configuration option 2020-01-24 11:24:25 +00:00
libgcc Add __gcov_indirect_call_profiler_v4_atomic. 2020-01-27 16:20:10 +01:00
libgfortran Add `--with-toolexeclibdir=' configuration option 2020-01-24 11:24:25 +00:00
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libhsail-rt Add `--with-toolexeclibdir=' configuration option 2020-01-24 11:24:25 +00:00
libiberty [libiberty] output empty args as a pair of quotes 2020-01-23 16:45:24 -03:00
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libssp Add `--with-toolexeclibdir=' configuration option 2020-01-24 11:24:25 +00:00
libstdc++-v3 Fix 2 typos in documentation of libstdc++. 2020-01-28 10:25:30 +01:00
libvtv Add `--with-toolexeclibdir=' configuration option 2020-01-24 11:24:25 +00:00
lto-plugin Update copyright years. 2020-01-01 12:51:42 +01:00
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.dir-locals.el
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.gitignore Add .clangd and compile_commands.json to .gitignore. 2019-08-28 19:33:28 +00:00
ABOUT-NLS
ar-lib Update GCC to autoconf 2.69, automake 1.15.1 (PR bootstrap/82856). 2018-10-31 17:03:16 +00:00
ChangeLog Add *.md diff=md. 2020-01-15 14:29:53 +01:00
ChangeLog.jit
ChangeLog.tree-ssa
compile
config-ml.in MSP430: Add -fno-exceptions multilib 2019-12-11 19:19:50 +00:00
config.guess Update config.sub and config.guess. 2019-09-09 11:14:32 +02:00
config.rpath
config.sub Update config.sub and config.guess. 2019-09-09 11:14:32 +02:00
configure configure.ac: Factor out common cases for compare_exclusions. 2019-12-11 20:59:35 +00:00
configure.ac configure.ac: Factor out common cases for compare_exclusions. 2019-12-11 20:59:35 +00:00
COPYING
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depcomp
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libtool.m4 [ARM/FDPIC v6 02/24] [ARM] FDPIC: Handle arm*-*-uclinuxfdpiceabi in configure scripts 2019-09-10 09:37:00 +02:00
ltgcc.m4
ltmain.sh libtool.m4: Sort output of 'find' to enable deterministic builds. 2018-07-05 13:13:45 -06:00
ltoptions.m4
ltsugar.m4
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lt~obsolete.m4
MAINTAINERS MAINTAINERS: Update my email address. 2020-01-13 22:10:14 +03:00
Makefile.def Sync top-level change from gdb 2019-06-15 21:32:03 +00:00
Makefile.in Makefile.tpl (HOST_EXPORTS): Add CXX_FOR_BUILD. 2019-08-23 15:37:22 -06:00
Makefile.tpl Makefile.tpl (HOST_EXPORTS): Add CXX_FOR_BUILD. 2019-08-23 15:37:22 -06:00
missing
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multilib.am Update GCC to autoconf 2.69, automake 1.15.1 (PR bootstrap/82856). 2018-10-31 17:03:16 +00:00
README
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test-driver Update GCC to autoconf 2.69, automake 1.15.1 (PR bootstrap/82856). 2018-10-31 17:03:16 +00:00
ylwrap

This directory contains the GNU Compiler Collection (GCC).

The GNU Compiler Collection is free software.  See the files whose
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