On Wed, Dec 19, 2018 at 10:33 AM Alejandro Martinez Vicente
<alejandro.martinezvice...@arm.com> wrote:
>
> Hi all,
>
> Loops that use the fmin/fmax builtins can be vectorized even without
> -ffast-math using SVE's FMINNM/FMAXNM instructions. This is an example:
>
> double
> f (double *x, int n)
> {
> double res = 100.0;
> for (int i = 0; i < n; ++i)
> res = __builtin_fmin (res, x[i]);
> return res;
> }
>
> Before this patch, the compiler would generate this code (-march=armv8.2-a+sve
> -O2 -ftree-vectorize):
>
> 0000000000000000 <f>:
> 0: 7100003f cmp w1, #0x0
> 4: 5400018d b.le 34 <f+0x34>
> 8: 51000422 sub w2, w1, #0x1
> c: 91002003 add x3, x0, #0x8
> 10: d2e80b21 mov x1, #0x4059000000000000
> 14: 9e670020 fmov d0, x1
> 18: 8b224c62 add x2, x3, w2, uxtw #3
> 1c: d503201f nop
> 20: fc408401 ldr d1, [x0],#8
> 24: 1e617800 fminnm d0, d0, d1
> 28: eb02001f cmp x0, x2
> 2c: 54ffffa1 b.ne 20 <f+0x20>
> 30: d65f03c0 ret
> 34: d2e80b20 mov x0, #0x4059000000000000
> 38: 9e670000 fmov d0, x0
> 3c: d65f03c0 ret
>
> After this patch, this is the code that gets generated:
>
> 0000000000000000 <f>:
> 0: 7100003f cmp w1, #0x0
> 4: 5400020d b.le 44 <f+0x44>
> 8: d2800002 mov x2, #0x0
> c: 25d8e3e0 ptrue p0.d
> 10: 93407c21 sxtw x1, w1
> 14: 90000003 adrp x3, 0 <f>
> 18: 25804001 mov p1.b, p0.b
> 1c: 91000063 add x3, x3, #0x0
> 20: 85c0e060 ld1rd {z0.d}, p0/z, [x3]
> 24: 25e11fe0 whilelo p0.d, xzr, x1
> 28: a5e24001 ld1d {z1.d}, p0/z, [x0, x2, lsl #3]
> 2c: 04f0e3e2 incd x2
> 30: 65c58020 fminnm z0.d, p0/m, z0.d, z1.d
> 34: 25e11c40 whilelo p0.d, x2, x1
> 38: 54ffff81 b.ne 28 <f+0x28> // b.any
> 3c: 65c52400 fminnmv d0, p1, z0.d
> 40: d65f03c0 ret
> 44: d2e80b20 mov x0, #0x4059000000000000
> 48: 9e670000 fmov d0, x0
> 4c: d65f03c0 ret
>
> This patch extends the support for reductions to include calls to internal
> functions, in addition to assign statements. For this purpose, in most places
> where a tree_code would be used, a code_helper is used instead. The
> code_helper
> allows to hold either a tree_code or combined_fn.
>
> This patch implements these tasks:
>
> - Detect a reduction candidate based on a call to an internal function
> (currently only fmin or fmax).
> - Process the reduction using code_helper. This means that at several places
> we have to check whether this is as assign-based reduction or a call-based
> reduction.
> - Add new internal functions for the fmin/fmax reductions and for conditional
> fmin/fmax. In architectures where ieee fmin/fmax reductions are available,
> it
> is still possible to vectorize the loop using unconditional instructions.
> - Update SVE's md to support these new reductions.
> - Add new SVE tests to check that the optimal code is being generated.
>
> I tested this patch in an aarch64 machine bootstrapping the compiler and
> running the checks.
Just some quick comments based on the above and the changelog.
Using code_helper is reasonable I guess.
> Alejandro
>
> gcc/Changelog:
>
> 2018-12-18 Alejandro Martinez <alejandro.martinezvice...@arm.com>
>
> * gimple-match.h (code_helper_for_stmnt): New function to get a
code_helper_for_stmt I hope.
> code_helper from an statement.
> * internal-fn.def: New reduc_fmax_scal and reduc_fmin_scal optabs for
> ieee fp max/min reductions
Aren't they necessarily fold_left reductions then? Thus, should the optabs
be named accordingly fold_left_fmax_optab?
> * optabs.def: Likewise.
> * tree-vect-loop.c (reduction_fn_for_scalar_code): Changed function
> signature to accept code_helper instead of tree_code. Handle the
> fmax/fmin builtins.
> (needs_fold_left_reduction_p): Likewise.
> (check_reduction_path): Likewise.
> (vect_is_simple_reduction): Use code_helper instead of tree_code.
> Check
> for supported call-based reductions. Extend support for both
> assignment-based and call-based reductions.
> (vect_model_reduction_cost): Extend cost-model support to call-based
> reductions (just use MAX expression).
> (get_initial_def_for_reduction): Use code_helper instead of tree_code.
> Extend support for both assignment-based and call-based reductions.
> (vect_create_epilog_for_reduction): Likewise.
> (vectorizable_reduction): Likewise.
> * tree-vectorizer.h: include gimple-match.h for code_helper. Use
> code_helper in check_reduction_path signature.
> * config/aarch64/aarch64-sve.md: Added define_expand to capture new
> reduc_fmax_scal and reduc_fmin_scal optabs.
> * config/aarch64/iterators.md: New FMAXMINNMV and fmaxmin_uns
> iterators
> to support the new define_expand.
>
> gcc/testsuite/Changelog:
>
> 2018-12-18 Alejandro Martinez <alejandro.martinezvice...@arm.com>
>
> * gcc.target/aarch64/sve/reduc_9.c: New test to check
> SVE-vectorized reductions without -ffast-math.
> * gcc.target/aarch64/sve/reduc_10.c: New test to check
> SVE-vectorized builtin reductions without -ffast-math.
