PR tree-optimization/50789
	* tree-vect-stmts.c (process_use): Add force argument, avoid
	exist_non_indexing_operands_for_use_p check if true.
	(vect_mark_stmts_to_be_vectorized): Adjust callers.  Handle
	STMT_VINFO_GATHER_P.
	(gen_perm_mask): New function.
	(perm_mask_for_reverse): Use it.
	(reverse_vec_element): Rename to...
	(permute_vec_elements): ... this.  Add Y and MASK_VEC arguments,
	generalize for any permutations.
	(vectorizable_load): Adjust caller.  Handle STMT_VINFO_GATHER_P.
	* target.def (TARGET_VECTORIZE_BUILTIN_GATHER): New hook.
	* doc/tm.texi.in (TARGET_VECTORIZE_BUILTIN_GATHER): Document it.
	* doc/tm.texi: Regenerate.
	* tree-data-ref.c (initialize_data_dependence_relation,
	compute_self_dependence): No longer static.
	* tree-data-ref.h (initialize_data_dependence_relation,
	compute_self_dependence): New prototypes.
	* tree-vect-data-refs.c (vect_check_gather): New function.
	(vect_analyze_data_refs): Detect possible gather load data
	refs.
	* tree-vectorizer.h (struct _stmt_vec_info): Add gather_p field.
	(STMT_VINFO_GATHER_P): Define.
	(vect_check_gather): New prototype.
	* config/i386/i386-builtin-types.def: Add types for alternate
	gather builtins.
	* config/i386/sse.md (AVXMODE48P_DI): Remove.
	(VEC_GATHER_MODE): Rename mode_attr to...
	(VEC_GATHER_IDXSI): ... this.
	(VEC_GATHER_IDXDI, VEC_GATHER_SRCDI): New mode_attrs.
	(avx2_gathersi<mode>, *avx2_gathersi<mode>): Use <VEC_GATHER_IDXSI>
	instead of <VEC_GATHER_MODE>.
	(avx2_gatherdi<mode>): Use <VEC_GATHER_IDXDI> instead of
	<<AVXMODE48P_DI> and <VEC_GATHER_SRCDI> instead of VEC_GATHER_MODE
	on src and mask operands.
	(*avx2_gatherdi<mode>): Likewise.  Use VEC_GATHER_MODE iterator
	instead of AVXMODE48P_DI.
	(avx2_gatherdi<mode>256, *avx2_gatherdi<mode>256): Removed.
	* config/i386/i386.c (enum ix86_builtins): Add
	IX86_BUILTIN_GATHERALTSIV4DF, IX86_BUILTIN_GATHERALTDIV8SF,
	IX86_BUILTIN_GATHERALTSIV4DI and IX86_BUILTIN_GATHERALTDIV8SI.
	(ix86_init_mmx_sse_builtins): Create those builtins.
	(ix86_expand_builtin): Handle those builtins and adjust expansions
	of other gather builtins.
	(ix86_vectorize_builtin_gather): New function.
	(TARGET_VECTORIZE_BUILTIN_GATHER): Define.

	* gcc.target/i386/avx2-gather-1.c: New test.
	* gcc.target/i386/avx2-gather-2.c: New test.
	* gcc.target/i386/avx2-gather-3.c: New test.
	* gcc.target/i386/avx2-gather-4.c: New test.

From-SVN: r181089