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| author | Sandra Loosemore <sloosemore@baylibre.com> | 2025-04-15 18:37:37 +0000 |
|---|---|---|
| committer | Sandra Loosemore <sloosemore@baylibre.com> | 2025-04-15 19:18:27 +0000 |
| commit | d91aab4dd6814ca54c211a93fec3f072745a52c4 (patch) | |
| tree | fb578eb55ed4e5c443f417b48c8433536895cac6 /gcc | |
| parent | 628aecb050bbbc4bb0bd4468c474623e20d64e21 (diff) | |
| download | gcc-d91aab4dd6814ca54c211a93fec3f072745a52c4.zip gcc-d91aab4dd6814ca54c211a93fec3f072745a52c4.tar.gz gcc-d91aab4dd6814ca54c211a93fec3f072745a52c4.tar.bz2 | |
Docs: Address -fivopts, -O0, and -Q confusion [PR71094]
There's a blurb at the top of the "Optimize Options" node telling
people that most optimization options are completely disabled at -O0
and a similar blurb in the entry for -Og, but nothing at the entry for
-O0. Since this is a continuing point of confusion it seems wise to
duplicate the information in all the places users are likely to look
for it.
gcc/ChangeLog
PR tree-optimization/71094
* doc/invoke.texi (Optimize Options): Document that -fivopts is
enabled at -O1 and higher. Add blurb about -O0 causing GCC to
completely ignore most optimization options.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/doc/invoke.texi | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index b99da94..0b6644b 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -12746,6 +12746,7 @@ complexity than at @option{-O}. -fipa-pure-const -fipa-reference -fipa-reference-addressable +-fivopts -fmerge-constants -fmove-loop-invariants -fmove-loop-stores @@ -12854,6 +12855,13 @@ by @option{-O2} and also turns on the following optimization flags: Reduce compilation time and make debugging produce the expected results. This is the default. +At @option{-O0}, GCC completely disables most optimization passes; +they are not run even if you explicitly enable them on the command +line, or are listed by @option{-Q --help=optimizers} as being enabled by +default. Many optimizations performed by GCC depend on code analysis +or canonicalization passes that are enabled by @option{-O}, and it would +not be useful to run individual optimization passes in isolation. + @opindex Os @item -Os Optimize for size. @option{-Os} enables all @option{-O2} optimizations @@ -14306,6 +14314,7 @@ Enabled by default at @option{-O1} and higher. @item -fivopts Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees. +Enabled by default at @option{-O1} and higher. @opindex ftree-parallelize-loops @item -ftree-parallelize-loops=n |