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| author | Paolo Bonzini <bonzini@gnu.org> | 2009-04-11 00:43:33 +0000 |
|---|---|---|
| committer | H.J. Lu <hjl@gcc.gnu.org> | 2009-04-10 17:43:33 -0700 |
| commit | 567a90f59cd53598b49d52fe079d025ec8752ca1 (patch) | |
| tree | ce35741803e4b49332cd8345a4ec57c833a70ba1 | |
| parent | 1f544684434f7058560b224cccd2286585e70ea2 (diff) | |
| download | gcc-567a90f59cd53598b49d52fe079d025ec8752ca1.tar.gz | |
re PR middle-end/39701 (Revision 145846 caused many test failures)
2009-04-10 Paolo Bonzini <bonzini@gnu.org>
PR tree-optimization/39701
* doc/invoke.texi (Optimization Options): Document change in
meaning and initialization of -fdelete-null-pointer-checks.
From-SVN: r145948
| -rw-r--r-- | gcc/ChangeLog | 6 | ||||
| -rw-r--r-- | gcc/doc/invoke.texi | 23 |
2 files changed, 20 insertions, 9 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index c61b4cde606..24e0f46f56f 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +2009-04-10 Paolo Bonzini <bonzini@gnu.org> + + PR tree-optimization/39701 + * doc/invoke.texi (Optimization Options): Document change in + meaning and initialization of -fdelete-null-pointer-checks. + 2009-04-10 H.J. Lu <hongjiu.lu@intel.com> PR middle-end/39701 diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index e87de62049a..a09ce75d362 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -5888,17 +5888,22 @@ Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fdelete-null-pointer-checks @opindex fdelete-null-pointer-checks -Use global dataflow analysis to identify and eliminate useless checks -for null pointers. The compiler assumes that dereferencing a null -pointer would have halted the program. If a pointer is checked after -it has already been dereferenced, it cannot be null. - -In some environments, this assumption is not true, and programs can -safely dereference null pointers. Use -@option{-fno-delete-null-pointer-checks} to disable this optimization +Assume that programs cannot safely dereference null pointers, and that +no code or data element resides there. This enables simple constant +folding optimizations at all optimization levels. In addition, other +optimization passes in GCC use this flag to control global dataflow +analyses that eliminate useless checks for null pointers; these assume +that if a pointer is checked after it has already been dereferenced, +it cannot be null. + +Note however that in some environments this assumption is not true. +Use @option{-fno-delete-null-pointer-checks} to disable this optimization for programs which depend on that behavior. -Enabled by default. +Some targets, especially embedded ones, disable this option at all levels. +Otherwise it is enabled at all levels: @option{-O0}, @option{-O1}, +@option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information +are enabled independently at different optimization levels. @item -fexpensive-optimizations @opindex fexpensive-optimizations |