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Re: [tree-ssa]: PRE updates

On Wed, 2003-06-11 at 09:27, Andrew MacLeod wrote:

> SO the code you are looking at above created thge a_5 PHI stmt... Its
> a_5 I am creating the var_ann for, because I just created it out of thin
> air.
But wait, var_ann(a_5) *must* be the same as var_ann(a_4) which is
var_ann(a).  SSA_NAMEs do not have annotations, their associated
VAR_DECLs do.  So, if you are only creating a new SSA_NAME for a
VAR_DECL that has been referenced already, then that VAR_DECL should
already have an annotation.

So, I still wonder why VAR_DECL 'a' didn't have an annotation.  It

> Index: tree-cfg.c
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/Attic/tree-cfg.c,v
> retrieving revision
> diff -c -p -r1.1.4.104 tree-cfg.c
> *** tree-cfg.c	9 Jun 2003 22:37:01 -0000
> --- tree-cfg.c	11 Jun 2003 13:19:49 -0000
> *************** handle_switch_split (basic_block src, ba
> *** 3677,3684 ****
> --- 3677,3688 ----
>   	  for (; phi; phi = TREE_CHAIN (phi))
>   	    {
>   	      tree new_phi;
> + 	      var_ann_t ann;
>   	      new_phi = create_phi_node (SSA_NAME_VAR (PHI_RESULT (phi)),
>   					 new_bb);
> + 	      ann = create_var_ann (PHI_RESULT (new_phi));
> + 	      ann->has_real_refs = var_ann (PHI_RESULT (phi))->has_real_refs;
> + 
Hmm, create_var_ann() shouldn't allow creating annotations on
SSA_NAMEs.  We may want to change that, but in the current
implementation the above is wrong: var_ann (PHI_RESULT (phi)) will never
access the annotation you just created.  The first thing var_ann() does
is peel the SSA_NAME wrapper to get at the VAR_DECL.

Which brings me to the real issue.  Is it the case that we want to have
annotations on SSA_NAMEs instead of the _DECLs that they wrap?  That is
a non-trivial change because var_ann_d describes attributes for
VAR_DECLs.  Those attributes are shared by all the SSA_NAMEs created for
that _DECL.


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