[PATCH, rs6000] Do not do gimple-folding of expressions that are missing their LHS

[Bill Schmidt]

Although I said this was invalid code, it really isn't -- it's legal code.  It's more of an ice-on-stupid-code situation. :)  So probably you should remove the "invalid" language from the commentary.  Sorry for misleading you.

-- Bill

Bill Schmidt, Ph.D.
GCC for Linux on Power
Linux on Power Toolchain
IBM Linux Technology Center
wschmidt@linux.vnet.ibm.com

> On Jul 12, 2017, at 11:45 AM, Will Schmidt <will_schmidt@vnet.ibm.com> wrote:
> 
> Hi,
> 
> 
> Do not do the gimple-folding optimizations of expressions that are
> missing their LHS.  (Preventing an ICE on invalid code).
> 
> This was noticed during debug of PR81317, but is not a fix for that PR.
> This is based on a patch suggested by Segher.
> 
> (This will need a revisit if/when we get as far as doing early gimple
> folding for expressions without a lhs, but for now, this seems sufficient).
> 
> This seems straightforward.  regtest going on ppc64LE just in case.
> OK for trunk?
> 
> [gcc]
> 
> 	2017-07-12  Will Schmidt  <will_schmidt@vnet.ibm.com>
> 
> 	* config/rs6000/rs6000.c (rs6000_gimple_fold_builtin): Return
> 	early if there is no lhs.
> 
> [gcc/testsuite]
> 
> 	2017-07-12  Will Schmidt  <will_schmidt@vnet.ibm.com>
> 
> 	* gcc.target/powerpc/fold-vec-missing-lhs.c: New.
> 
> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> index 10c5521..e21b56f 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -16297,6 +16297,9 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>     = (enum rs6000_builtins) DECL_FUNCTION_CODE (fndecl);
>   tree arg0, arg1, lhs;
> 
> +  /*  Generic solution to prevent gimple folding of code without a LHS.  */
> +  if (!gimple_call_lhs (stmt)) return false;
> +
>   switch (fn_code)
>     {
>     /* Flavors of vec_add.  We deliberately don't expand
> diff --git a/gcc/testsuite/gcc.target/powerpc/fold-vec-missing-lhs.c b/gcc/testsuite/gcc.target/powerpc/fold-vec-missing-lhs.c
> new file mode 100644
> index 0000000..d62f913
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/fold-vec-missing-lhs.c
> @@ -0,0 +1,24 @@
> +/* This test is meant to verify that the gimple-folding does not
> +occur when the LHS portion of an expression is missing.
> +Though we would consider this invalid code, this should not generate an ICE.
> +This was noticed during debug of PR81317.  */
> +
> +/* { dg-do compile } */
> +/* { dg-require-effective-target powerpc_altivec_ok } */
> +/* { dg-options "-maltivec" } */
> +
> +#include <altivec.h>
> +
> +vector signed short
> +test1_nolhs (vector bool short x, vector signed short y)
> +{
> +  vec_add (x, y);
> +  return vec_add (x, y);
> +}
> +
> +vector signed short
> +test2_nolhs (vector signed short x, vector bool short y)
> +{
> +  vec_add (x, y);
> +  return vec_add (x, y);
> +}
> 
>