[PATCH] Fix PR47566

[Ulrich Weigand]

Richard Guenther wrote:
> On Fri, 22 Jul 2011, Ulrich Weigand wrote:
> > Now that we have the linker plugin, this fails on spu-elf with:
> > 
> > /tmp/cce6KuRb.ltrans0.ltrans.o: In function `foo':
> > cce6KuRb.ltrans0.o:(.text+0x28): undefined reference to `sqrt'
> > 
> > because nothing links against libm.  I'm a bit confused by the comment
> > above: even with the linker plugin, where should libm be pulled in?
> > Don't we need to use -lm on the linker line anyway?
> 
> Well, the testcase was for an ICE which required that cabs is folded
> to sqrt(real**2 + imag**2), it requires "late" folding, thus
> -O0 during the compile step (it's a trick to use LTO here, to delay
> folding until after IPA opts).  Not linking with -lm and relying
> on a HW sqrt instruction makes sure we do that late folding
> which we want to happen.
> 
> So, if you can in any way retain all of the above features with
> fixing non-HW sqrt targets fine - otherwise I suggest you skip spu-elf.

Well, it works for me with just adding -lm to the dg-extra-ld-options.
This still folds cabs to sqrt in the LTO step, and then satisfies that
call via the libm routine ...  If I understood your intent correctly,
this should still test the same thing, shouldn't it?

Bye,
Ulrich

ChangeLog:

	* testsuite/gcc.dg/lto/20110201-1_0.c: Add -lm to dg-extra-ld-options.
	Update comment.

Index: gcc/testsuite/gcc.dg/lto/20110201-1_0.c
===================================================================
*** gcc/testsuite/gcc.dg/lto/20110201-1_0.c	(revision 176572)
--- gcc/testsuite/gcc.dg/lto/20110201-1_0.c	(working copy)
***************
*** 1,12 ****
  /* { dg-lto-do run } */
  /* { dg-lto-options { { -O0 -flto } } } */
! /* { dg-extra-ld-options "-O2 -ffast-math -fuse-linker-plugin" } */
  /* { dg-require-linker-plugin "" } */
  
! /* We require a linker plugin because otherwise we'd need to link
!    against libm which we are not sure here has cabs on all targets.
!    This is because collect2 invokes ld on the -O0 object code
!    which does not have folded cabs.  */
  
  double cabs(_Complex double);
  double __attribute__((used))
--- 1,14 ----
  /* { dg-lto-do run } */
  /* { dg-lto-options { { -O0 -flto } } } */
! /* { dg-extra-ld-options "-O2 -ffast-math -fuse-linker-plugin -lm" } */
  /* { dg-require-linker-plugin "" } */
  
! /* Since we compile with -O0, the object code will have a reference
!    to cabs.  The LTO link step will then fold this to either a call
!    to sqrt or a hardware square-root instruction.  We require the
!    linker plugin because otherwise a reference to cabs might remain
!    in the final output, which is not present on all targets.  We
!    still link against libm in case it is needed for sqrt.  */
  
  double cabs(_Complex double);
  double __attribute__((used))

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com