procyberian/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Document and test __builtin_expect_with_probability.

Browse source 
2019-07-09  Martin Liska  <mliska@suse.cz>

	* doc/extend.texi: Document influence on loop
	optimizers.
2019-07-09  Martin Liska  <mliska@suse.cz>

	* gcc.dg/predict-17.c: Test loop optimizer assumption
	about loop iterations.

From-SVN: r273295
This commit is contained in:
Martin Liska 2019-07-09 11:22:30 +02:00 • committed by Martin Liska
parent c2851dc289
commit b52db15861
4 changed files with 17 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
gcc/ChangeLog
View file

@ -6,6 +6,11 @@
(vn_reference_lookup_pieces): Adjust.
(vn_reference_lookup): Pass down original ref if we valueized.
2019-07-09 Martin Liska <mliska@suse.cz>
* doc/extend.texi: Document influence on loop
optimizers.
2019-07-09 Martin Liska <mliska@suse.cz>
* lto-compress.c (lto_normalized_zstd_level): Do not use

5
gcc/doc/extend.texi
View file

@ -13045,8 +13045,11 @@ when testing pointer or floating-point values.
For the purposes of branch prediction optimizations, the probability that
a @code{__builtin_expect} expression is @code{true} is controlled by GCC's
@code{builtin-expect-probability} parameter, which defaults to 90%.
You can also use @code{__builtin_expect_with_probability} to explicitly
assign a probability value to individual expressions.
assign a probability value to individual expressions. If the built-in
is used in a loop construct, the provided probability will influence
the expected number of iterations made by loop optimizations.
@end deftypefn
@deftypefn {Built-in Function} long __builtin_expect_with_probability

5
gcc/testsuite/ChangeLog
View file

@ -1,3 +1,8 @@
2019-07-09 Martin Liska <mliska@suse.cz>
* gcc.dg/predict-17.c: Test loop optimizer assumption
about loop iterations.
2019-07-09 Richard Biener <rguenther@suse.de>
* gcc.dg/tree-ssa/alias-access-path-1.c: Scan fre1 dump.

4
gcc/testsuite/gcc.dg/predict-17.c
View file

@ -1,5 +1,5 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
/* { dg-options "-O2 -fdump-tree-profile_estimate-details" } */
extern int global;
@ -11,3 +11,5 @@ void foo (int base)
/* { dg-final { scan-tree-dump "first match heuristics: 5.00%" "profile_estimate"} } */
/* { dg-final { scan-tree-dump "__builtin_expect_with_probability heuristics of edge .*->.*: 5.00%" "profile_estimate"} } */
/* { dg-final { scan-tree-dump "is probably executed at most 19" "profile_estimate"} } */