install.texi (Specific, [...]): Document need to bootstrap with -mips3.

	* doc/install.texi (Specific, mips-sgi-irix6): Document need to
	bootstrap with -mips3.

From-SVN: r53564

gcc/ChangeLog

+2002-05-17  Rainer Orth  <ro@TechFak.Uni-Bielefeld.DE>
+
+	* doc/install.texi (Specific, mips-sgi-irix6): Document need to
+	bootstrap with -mips3.
+
 2002-05-17  Kazu Hirata  <kazu@cs.umass.edu>
 
 	* final.c: Fix formatting.

gcc/doc/install.texi

@@ -3187,6 +3187,27 @@ then your version of @command{cc} uses the O32 or N64 ABI by default.  You
 should set the environment variable @env{CC} to @samp{cc -n32}
 before configuring GCC@.
 
+If you want the resulting @command{gcc} to run on old 32-bit systems
+with the MIPS R4400 CPU, you need to ensure that only code for the mips3
+instruction set architecture (ISA) is generated.  While GCC 3.x does
+this correctly, both GCC 2.95 and SGI's MIPSpro @command{cc} may change
+the ISA depending on the machine where GCC is built.  Using one of them
+as the bootstrap compiler may result in mips4 code, which won't run at
+all on mips3-only systems.  For the test program above, you should see:
+
+@example
+test.o: ELF N32 MSB mips-3 @dots{}
+@end example
+
+If you get:
+
+@example
+test.o: ELF N32 MSB mips-4 @dots{}
+@end example
+
+instead, you should set the environment variable @env{CC} to @samp{cc
+-n32 -mips3} or @samp{gcc -mips3} respectively before configuring GCC@.
+
 GCC on IRIX 6 is usually built to support both the N32 and N64 ABIs.  If
 you build GCC on a system that doesn't have the N64 libraries installed,
 you need to configure with @option{--disable-multilib} so GCC doesn't