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.
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 from an statement.
* internal-fn.def: New reduc_fmax_scal and reduc_fmin_scal optabs for
ieee fp max/min reductions
* 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.
final.patch
Description: final.patch
