[PATCH] Improve Store CCP for NULL DECL_INITIAL (PR 35402)

[Andrew_Pinski@PlayStation.Sony.Com]

Hi,
  When the DECL_INITIAL is NULL for read only variables, we don't 
propagate the default (zero) value to the code so we still reference the 
symbol.
This patch changes Store CPP to do this optimization for these variables. 
It only handles intergal and scalar float types because fold_convert does 
not handle many more types.

OK?  Bootstrapped and tested on i686-linux-gnu with no regressions.

Thanks,
Andrew Pinski

ChangeLog:

        * tree-ssa-ccp.c (get_symbol_constant_value): Handle
        integral and scalar float variables which have a
        NULL DECL_INITIAL.

        * gcc.dg/tree-ssa/ssa-store-ccp-1.c: New test.

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