Allow subregs around constant displacements [PR116516]

This patch fixes a regression introduced by g:708ee71808ea61758e73.
x86_64 allows addresses of the form:

  (zero_extend:DI (subreg:SI (symbol_ref:DI "foo") 0))

Before the previous patch, a lax SUBREG check meant that we would
treat the subreg as a base and reload it into a base register.
But that wasn't what the target was expecting.  Instead we should
treat "foo" as a constant displacement, to match:

	leal foo, <dest>

After the patch, we recognised that "foo" isn't a base register,
but ICEd on it rather than handling it as a displacement.

With or without the recent patches, if the address had instead been:

  (zero_extend:DI
    (subreg:SI (plus:DI (reg:DI R) (symbol_ref:DI "foo") 0)))

then we would have treated "foo" as the displacement and R as the base
or index, as expected.  The problem was that the code that does this was
rejecting all subregs of objects, rather than just subregs of variable
objects.

gcc/
	PR middle-end/116516
	* rtlanal.cc (strip_address_mutations): Allow subregs around
	constant displacements.

gcc/testsuite/
	PR middle-end/116516
	* gcc.c-torture/compile/pr116516.c: New test.

0 files changed, 0 insertions, 0 deletions