doc: mention STAGE1_CFLAGS

STAGE1_CFLAGS can be used to accelerate the just-built stage1 compiler
which especially improves its performance on some of the large generated
files during bootstrap. It defaults to nothing (i.e. -O0).

The downside is that if the native compiler is buggy, there's a greater
risk of a failed bootstrap. Those with a modern native compiler, ideally
a recent version of GCC, should be able to use -O1 or -O2 without issue
to get a faster build.

	PR rtl-optimization/111619
	* doc/install.texi (Building a native compiler): Discuss STAGE1_CFLAGS.

diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index fc771448274ae665cd202105d1bb7853717f2fce..576b7eead5ec1062dc5443671d3329b4fed00ac9 100644 (file)
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -3125,6 +3125,13 @@ Again, if the native compiler miscompiles the stage1 compiler, you may
 need to work around this by avoiding non-working parts of the stage1
 compiler.  Use @code{STAGE1_TFLAGS} to this end.
 
+You can use @code{STAGE1_CFLAGS} to set the flags passed to the host compiler
+when building the stage1 compiler.  The default is to pass @option{-g}, but when
+the host compiler is GCC, this results in a non-optimized build of the stage1
+compiler.  You can speed up the bootstrap by using @samp{STAGE1_CFLAGS='-O2'}
+at the increased risk of miscompiling the stage1 compiler when the host
+compiler is buggy.
+
 If you used the flag @option{--enable-languages=@dots{}} to restrict
 the compilers to be built, only those you've actually enabled will be
 built.  This will of course only build those runtime libraries, for