Update -ffunction/data-sections documentation

gcc/
	* doc/invoke.texi (ffunction-sections and fdata-sections):
	Update.

From-SVN: r253842

gcc/ChangeLog

+2017-10-18  Sebastian Huber  <sebastian.huber@embedded-brains.de>
+
+	* doc/invoke.texi (ffunction-sections and fdata-sections):
+	Update.
+
 2017-10-17  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* tree-ssa-loop-ivopts.c (add_autoinc_candidates): Bail out only if

gcc/doc/invoke.texi

@@ -9712,18 +9712,26 @@ file if the target supports arbitrary sections.  The name of the
 function or the name of the data item determines the section's name
 in the output file.
 
-Use these options on systems where the linker can perform optimizations
-to improve locality of reference in the instruction space.  Most systems
-using the ELF object format and SPARC processors running Solaris 2 have
-linkers with such optimizations.  AIX may have these optimizations in
-the future.
-
-Only use these options when there are significant benefits from doing
-so.  When you specify these options, the assembler and linker
-create larger object and executable files and are also slower.
-You cannot use @command{gprof} on all systems if you
-specify this option, and you may have problems with debugging if
-you specify both this option and @option{-g}.
+Use these options on systems where the linker can perform optimizations to
+improve locality of reference in the instruction space.  Most systems using the
+ELF object format have linkers with such optimizations.  On AIX, the linker
+rearranges sections (CSECTs) based on the call graph.  The performance impact
+varies.
+
+Together with a linker garbage collection (linker @option{--gc-sections}
+option) these options may lead to smaller statically-linked executables (after
+stripping).
+
+On ELF/DWARF systems these options do not degenerate the quality of the debug
+information.  There could be issues with other object files/debug info formats.
+
+Only use these options when there are significant benefits from doing so.  When
+you specify these options, the assembler and linker create larger object and
+executable files and are also slower.  These options affect code generation.
+They prevent optimizations by the compiler and assembler using relative
+locations inside a translation unit since the locations are unknown until
+link time.  An example of such an optimization is relaxing calls to short call
+instructions.
 
 @item -fbranch-target-load-optimize
 @opindex fbranch-target-load-optimize