[RFC ARM] Error if overriding --with-tune by --with-cpu

[James Greenhalgh <james dot greenhalgh at arm dot com>]

Hi,

We error in the case where both --with-tune and --with-cpu are specified at
configure time. In this case, we cannot distinguish this situation from the
situation where --with-tune was specified at configure time and -mcpu was
passed on the command line, so we give -mcpu precedence.

This might be surprising if you expect the precedence rules we give
to the command line options, but we can't change this precedence without
breaking our definition of -mcpu.

We also promote the warning which used to be thrown in the case of
--with-arch and --with-cpu to an error.

I've marked this is an RFC as it isn't clear that configure should be
catching something like this. Other blatant errors in configuration
options like passing "--with-languages=c,c++" pass without event.

Tested with a few combinations of configure options with no issues and the
expected behaviour.

Any opinions, and if not, OK for trunk?

Thanks,
James

---
gcc/

2014-05-30  James Greenhalgh  <james.greenhalgh@arm.com>

	* config.gcc (supported_defaults): Error when passing either
	--with-tune or --with-arch in conjunction with --with-cpu for ARM.

diff --git a/gcc/config.gcc b/gcc/config.gcc
index c3f3ea6..7e82700 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -3560,7 +3560,13 @@ case "${target}" in
 		esac
 
 		if test "x$with_arch" != x && test "x$with_cpu" != x; then
-			echo "Warning: --with-arch overrides --with-cpu=$with_cpu" 1>&2
+			echo "Switch \"--with-arch\" may not be used with switch \"--with-cpu\""  1>&2
+			exit 1
+		fi
+
+		if test "x$with_cpu" != x && test "x$with_tune" != x; then
+			echo "Switch \"--with-tune\" may not be used with switch \"--with-cpu\""  1>&2
+			exit 1
 		fi
 
 		# Add extra multilibs