expr.c: exapnd_expr() assumes TARGET bytes same as HOST bytes?

[Alan Lehotsky <apl at alum dot mit dot edu>]

In expand_expr(), the following

	/* Fold an expression like: "foo"[2].
	   This is not done in fold so it won't happen inside &.
	   Don't fold if this is for wide characters since it's too
	   difficult to do correctly and this is a very rare case.  */

	if (modifier != EXPAND_CONST_ADDRESS && modifier != EXPAND_INITIALIZER
	    && TREE_CODE (array) == STRING_CST
	    && TREE_CODE (index) == INTEGER_CST
	    && compare_tree_int (index, TREE_STRING_LENGTH (array)) < 0
	    && GET_MODE_CLASS (mode) == MODE_INT
	    && GET_MODE_SIZE (mode) == 1)
	  return
	    GEN_INT (TREE_STRING_POINTER (array)[TREE_INT_CST_LOW (index)]);


assumes that the HOST machine's bytes are the same size as the
target's bytes.  Cross compiling for a machine with 32 bit bytes
from a SPARC causes me to generate bad code for the executable test
921218-1.c because the SPARC sign-extends the fetched byte \0377.

I'm not quite sure if the fix for this should just  zero-or-sign
extend the character according to the value of DEFAULT_SIGNED_CHAR, or
if something more complex is required.

Any opinions?

-- Al