[PATCH] Fix tree-opt/21840, FRE/PRE mismatch types in MODIFY_EXPR

[Andrew Pinski <pinskia at physics dot uc dot edu>]

The problem here is that PRE/FRE forgets to add a cast if we going from
a void* to another type (like a function pointer).  Since x86 requires
the correct function type to be able to call the function, the cast is
really needed.  This is caught even without my patch attached in PR 
22368.

This patch fixes the type mismatch by converting the type to the correct
type.  The reason why this is safe is because we always get back either
a SSA_NAME or a constant and we can cast that expression and still be
valid gimple as we are always replacing the rhs of a MODIFY_EXPR.

OK? Bootstrapped and tested on powerpc-darwin with no regressions.


Thanks,
Andrew Pinski

ChangeLog:

	* tree-ssa-pre.c (eliminate): Convert the sprime to the correct type
	if *rhs_p is not a SSA_NAME.

testsuite/ChangeLog:

	* gcc.c-torture/compile/pr21840.c: New test.

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