This patch is the main part of PR85694. The aim is to recognise at least:
signed char *a, *b, *c;
...
for (int i = 0; i < 2048; i++)
c[i] = (a[i] + b[i]) >> 1;
as an over-widening pattern, since the addition and shift can be done
on shorts rather than ints. However, it ended up being a lot more
general than that.
The current over-widening pattern detection is limited to a few simple
cases: logical ops with immediate second operands, and shifts by a
constant. These cases are enough for common pixel-format conversion
and can be detected in a peephole way.
The loop above requires two generalisations of the current code: support
for addition as well as logical ops, and support for non-constant second
operands. These are harder to detect in the same peephole way, so the
patch tries to take a more global approach.
The idea is to get information about the minimum operation width
in two ways:
(1) by using the range information attached to the SSA_NAMEs
(effectively a forward walk, since the range info is
context-independent).
(2) by back-propagating the number of output bits required by
users of the result.
As explained in the comments, there's a balance to be struck between
narrowing an individual operation and fitting in with the surrounding
code. The approach is pretty conservative: if we could narrow an
operation to N bits without changing its semantics, it's OK to do that if:
- no operations later in the chain require more than N bits; or
- all internally-defined inputs are extended from N bits or fewer,
and at least one of them is single-use.
See the comments for the rationale.
I didn't bother adding STMT_VINFO_* wrappers for the new fields
since the code seemed more readable without.
2018-06-20 Richard Sandiford <richard.sandiford@arm.com>
gcc/
* poly-int.h (print_hex): New function.
* dumpfile.h (dump_dec, dump_hex): Declare.
* dumpfile.c (dump_dec, dump_hex): New poly_wide_int functions.
* tree-vectorizer.h (_stmt_vec_info): Add min_output_precision,
min_input_precision, operation_precision and operation_sign.
* tree-vect-patterns.c (vect_get_range_info): New function.
(vect_same_loop_or_bb_p, vect_single_imm_use)
(vect_operation_fits_smaller_type): Delete.
(vect_look_through_possible_promotion): Add an optional
single_use_p parameter.
(vect_recog_over_widening_pattern): Rewrite to use new
stmt_vec_info infomration. Handle one operation at a time.
(vect_recog_cast_forwprop_pattern, vect_narrowable_type_p)
(vect_truncatable_operation_p, vect_set_operation_type)
(vect_set_min_input_precision): New functions.
(vect_determine_min_output_precision_1): Likewise.
(vect_determine_min_output_precision): Likewise.
(vect_determine_precisions_from_range): Likewise.
(vect_determine_precisions_from_users): Likewise.
(vect_determine_stmt_precisions, vect_determine_precisions): Likewise.
(vect_vect_recog_func_ptrs): Put over_widening first.
Add cast_forwprop.
(vect_pattern_recog): Call vect_determine_precisions.
gcc/testsuite/
* gcc.dg/vect/vect-widen-mult-u8-u32.c: Check specifically for a
widen_mult pattern.
* gcc.dg/vect/vect-over-widen-1.c: Update the scan tests for new
over-widening messages.
* gcc.dg/vect/vect-over-widen-1-big-array.c: Likewise.
* gcc.dg/vect/vect-over-widen-2.c: Likewise.
* gcc.dg/vect/vect-over-widen-2-big-array.c: Likewise.
* gcc.dg/vect/vect-over-widen-3.c: Likewise.
* gcc.dg/vect/vect-over-widen-3-big-array.c: Likewise.
* gcc.dg/vect/vect-over-widen-4.c: Likewise.
* gcc.dg/vect/vect-over-widen-4-big-array.c: Likewise.
* gcc.dg/vect/bb-slp-over-widen-1.c: New test.
* gcc.dg/vect/bb-slp-over-widen-2.c: Likewise.
* gcc.dg/vect/vect-over-widen-5.c: Likewise.
* gcc.dg/vect/vect-over-widen-6.c: Likewise.
* gcc.dg/vect/vect-over-widen-7.c: Likewise.
* gcc.dg/vect/vect-over-widen-8.c: Likewise.
* gcc.dg/vect/vect-over-widen-9.c: Likewise.
* gcc.dg/vect/vect-over-widen-10.c: Likewise.
* gcc.dg/vect/vect-over-widen-11.c: Likewise.
* gcc.dg/vect/vect-over-widen-12.c: Likewise.
* gcc.dg/vect/vect-over-widen-13.c: Likewise.
* gcc.dg/vect/vect-over-widen-14.c: Likewise.
* gcc.dg/vect/vect-over-widen-15.c: Likewise.
* gcc.dg/vect/vect-over-widen-16.c: Likewise.
* gcc.dg/vect/vect-over-widen-17.c: Likewise.
* gcc.dg/vect/vect-over-widen-18.c: Likewise.
* gcc.dg/vect/vect-over-widen-19.c: Likewise.
* gcc.dg/vect/vect-over-widen-20.c: Likewise.
* gcc.dg/vect/vect-over-widen-21.c: Likewise.
From-SVN: r262333
