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[PATCH] Change default optimization level to -Og


GCC's default optimization level is -O0.  Unfortunately unlike other compilers,
GCC generates extremely inefficient code with -O0.  It is almost unusable for
low-level debugging or manual inspection of generated code.  So a -O option is
always required for compilation.  -Og not only allows for fast compilation, but
also produces code that is efficient, readable as well as debuggable.
Therefore -Og makes for a much better default setting.

Any comments?

2017-10-26  Wilco Dijkstra  <wdijkstr@arm.com>

	* opts.c (default_options_optimization): Set default to -Og.

doc/
	* invoke.texi (-O0) Remove default mention.
	(-Og): Add mention of default setting.

--
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 3328a3b5fafa6a98007eff52d2a26af520de9128..74c33ea35b9f320b419a3417e6007d2391536f1b 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -7343,7 +7343,7 @@ by @option{-O2} and also turns on the following optimization flags:
 @item -O0
 @opindex O0
 Reduce compilation time and make debugging produce the expected
-results.  This is the default.
+results.
 
 @item -Os
 @opindex Os
@@ -7371,7 +7371,7 @@ Optimize debugging experience.  @option{-Og} enables optimizations
 that do not interfere with debugging. It should be the optimization
 level of choice for the standard edit-compile-debug cycle, offering
 a reasonable level of optimization while maintaining fast compilation
-and a good debugging experience.
+and a good debugging experience.  This is the default.
 @end table
 
 If you use multiple @option{-O} options, with or without level numbers,
diff --git a/gcc/opts.c b/gcc/opts.c
index dfad955e220870a3250198640f3790c804b191e0..74511215309f11445685db4894be2ab6881695d3 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -565,6 +565,12 @@ default_options_optimization (struct gcc_options *opts,
   int opt2;
   bool openacc_mode = false;
 
+  /* Set the default optimization to -Og.  */
+  opts->x_optimize_size = 0;
+  opts->x_optimize = 1;
+  opts->x_optimize_fast = 0;
+  opts->x_optimize_debug = 1;
+
   /* Scan to see what optimization level has been specified.  That will
      determine the default value of many flags.  */
   for (i = 1; i < decoded_options_count; i++)


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