can detect state of -fomit-frame-pointer at compile time?

[Doug Evans <dje at transmeta dot com>]

Scott A Sumner writes:
 > Hi,
 > 
 > Can I do something like the following?  If so, can anyone help me out
 > with the exact syntax?
 > 
 > #if (compiling using -fomit-frame-pointer)
 >    // do this
 > #else
 >    // do that
 > #endif

There is a way to accomplish this but it's a hack.
I only mention it here for information's sake.
I don't recommend doing this.
Instead, have your Makefile specify the appropriate thing.

What you want to do is create your own specs
file and have it predefine something if -fomit-frame-pointer
is specified.

N.B. The -B./ argument below is used to tell gcc where to
find the specs file.  Make sure there is nothing else in
the directory that you don't want gcc to use.
[e.g. having a symlink called `as' to /bin/sh would not be
a good idea :-)  [sh won't understand the arguments anyway
but you get the point]]

On my i386-linux box:
---
gcc -dumpspecs >specs

Edit specs and apply this:

--- specs.~1~	Fri Mar 17 17:49:01 2000
+++ specs	Fri Mar 17 17:49:26 2000
@@ -5,7 +5,7 @@
 %|
 
 *cpp:
-%(cpp_cpu) %{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}
+%(cpp_cpu) %{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT} %{fomit-frame-pointer:-DFOMIT_FRAME_POINTER}
 
 *cc1:
 %(cc1_cpu) %{profile:-p}


---
foo.c:
#ifdef FOMIT_FRAME_POINTER
int omitted;
#else
int nope;
#endif
---
gcc -B./ -E foo.c

# 1 "foo.c"



int nope;

---
gcc -B./ -E -fomit-frame-pointer foo.c

# 1 "foo.c"

int omitted;



---

------
Want more information?  See the CrossGCC FAQ, http://www.objsw.com/CrossGCC/
Want to unsubscribe? Send a note to crossgcc-unsubscribe@sourceware.cygnus.com