aarch64: Fix aarch64 backend-use of (u|s|us)dot_prod patterns

aarch64: Fix aarch64 backend-use of (u|s|us)dot_prod patterns

Given recent changes to the dot_prod standard pattern name, this patch
fixes the aarch64 back-end by implementing the following changes:

1. Add 2nd mode to all (u|s|us)dot_prod patterns in .md files.
2. Rewrite initialization and function expansion mechanism for simd
builtins.
3. Fix all direct calls to back-end `dot_prod' patterns in SVE
builtins.

Finally, given that it is now possible for the compiler to
differentiate between the two- and four-way dot product, we add a test
to ensure that autovectorization picks up on dot-product patterns
where the result is twice the width of the operands.

gcc/ChangeLog:

	* config/aarch64/aarch64-simd.md
	(<sur>dot_prod<vsi2qi><vczle><vczbe>): Renamed to...
	(<sur>dot_prod<mode><vsi2qi><vczle><vczbe>): ...this.
	(usdot_prod<vsi2qi><vczle><vczbe>): Renamed to...
	(usdot_prod<mode><vsi2qi><vczle><vczbe>): ...this.
	(<su>sadv16qi): Adjust call to gen_udot_prod take second mode.
	(popcount<mode2>): fix use of `udot_prod_optab'.
	* config/aarch64/aarch64-sve.md
	(<sur>dot_prod<vsi2qi>): Renamed to...
	(<sur>dot_prod<mode><vsi2qi>): ...this.
	(@<sur>dot_prod<vsi2qi>): Renamed to...
	(@<sur>dot_prod<mode><vsi2qi>): ...this.
	(<su>sad<vsi2qi>): Adjust call to gen_udot_prod take second mode.
	* config/aarch64/aarch64-sve2.md
	(@aarch64_sve_<sur>dotvnx4sivnx8hi): Renamed to...
	(<sur>dot_prodvnx4sivnx8hi): ...this.
	* config/aarch64/aarch64-simd-builtins.def: Modify macro
	expansion-based initialization and expansion
	of (u|s|us)dot_prod builtins.
	* config/aarch64/aarch64-builtins.cc
	(CODE_FOR_aarch64_sdot_prodv8qi): Define as alias to
	new CODE_FOR_sdot_prodv2siv8qi.
	(CODE_FOR_aarch64_udot_prodv8qi): Define as alias to
	new CODE_FOR_udot_prodv2siv8qi.
	(CODE_FOR_aarch64_usdot_prodv8qi): Define as alias to
	new CODE_FOR_usdot_prodv2siv8qi.
	(CODE_FOR_aarch64_sdot_prodv16qi): Define as alias to
	new CODE_FOR_sdot_prodv4siv16qi.
	(CODE_FOR_aarch64_udot_prodv16qi): Define as alias to
	new CODE_FOR_udot_prodv4siv16qi.
	(CODE_FOR_aarch64_usdot_prodv16qi): Define as alias to
	new CODE_FOR_usdot_prodv4siv16qi.
	* config/aarch64/aarch64-sve-builtins-base.cc
	(svdot_impl::expand): s/direct/convert/ in
	`convert_optab_handler_for_sign' function call.
	(svusdot_impl::expand): add second mode argument in call to
	`code_for_dot_prod'.
	* config/aarch64/aarch64-sve-builtins.cc
	(function_expander::convert_optab_handler_for_sign): New class
	method.
	* config/aarch64/aarch64-sve-builtins.h
	(class function_expander): Add prototype for new
	`convert_optab_handler_for_sign' method.

gcc/testsuite/ChangeLog:
	* gcc.target/aarch64/sme/vect-dotprod-twoway.c (udot2): New.