This patch folds certain reductions of X & CST to X[I] & CST[I] if I is the only nonzero element of CST. This includes the motivating case in which CST[I] is -1.
We could do the same for REDUC_MAX on unsigned types, but I wasn't sure that that special case was worth it. Tested on aarch64-linux-gnu, aarch64_be-elf and x86_64-linux-gnu. OK to install? Obvious follow-ons include handling multiplications of single_nonzero_element constants, multiplications of uniform constants, and additions of any constant, but this is enough to fix the PR. Richard 2019-01-04 Richard Sandiford <richard.sandif...@arm.com> gcc/ PR tree-optimization/88598 * tree.h (single_nonzero_element): Declare. * tree.c (single_nonzero_element): New function. * match.pd: Fold certain reductions of X & CST to X[I] & CST[I] if I is the only nonzero element of CST. gcc/testsuite/ PR tree-optimization/88598 * gcc.dg/vect/pr88598-1.c: New test. * gcc.dg/vect/pr88598-2.c: Likewise. * gcc.dg/vect/pr88598-3.c: Likewise. * gcc.dg/vect/pr88598-4.c: Likewise. * gcc.dg/vect/pr88598-5.c: Likewise. * gcc.dg/vect/pr88598-6.c: Likewise. Index: gcc/tree.h =================================================================== --- gcc/tree.h 2019-01-04 11:40:33.141683783 +0000 +++ gcc/tree.h 2019-01-04 11:40:36.581654424 +0000 @@ -4522,6 +4522,8 @@ extern tree uniform_vector_p (const_tree extern tree uniform_integer_cst_p (tree); +extern int single_nonzero_element (const_tree); + /* Given a CONSTRUCTOR CTOR, return the element values as a vector. */ extern vec<tree, va_gc> *ctor_to_vec (tree); Index: gcc/tree.c =================================================================== --- gcc/tree.c 2019-01-04 11:40:33.141683783 +0000 +++ gcc/tree.c 2019-01-04 11:40:36.577654458 +0000 @@ -11355,6 +11355,38 @@ uniform_integer_cst_p (tree t) return NULL_TREE; } +/* If VECTOR_CST T has a single nonzero element, return the index of that + element, otherwise return -1. */ + +int +single_nonzero_element (const_tree t) +{ + unsigned HOST_WIDE_INT nelts; + unsigned int repeat_nelts; + if (VECTOR_CST_NELTS (t).is_constant (&nelts)) + repeat_nelts = nelts; + else if (VECTOR_CST_NELTS_PER_PATTERN (t) == 2) + { + nelts = vector_cst_encoded_nelts (t); + repeat_nelts = VECTOR_CST_NPATTERNS (t); + } + else + return -1; + + int res = -1; + for (unsigned int i = 0; i < nelts; ++i) + { + tree elt = vector_cst_elt (t, i); + if (!integer_zerop (elt) && !real_zerop (elt)) + { + if (res >= 0 || i >= repeat_nelts) + return -1; + res = i; + } + } + return res; +} + /* Build an empty statement at location LOC. */ tree Index: gcc/match.pd =================================================================== --- gcc/match.pd 2019-01-04 11:40:33.137683817 +0000 +++ gcc/match.pd 2019-01-04 11:40:36.573654492 +0000 @@ -5251,3 +5251,19 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) { wide_int_to_tree (sizetype, off); }) { swap_p ? @0 : @2; })) { rhs_tree; }))))))))) + +/* Fold REDUC (@0 & @1) -> @0[I] & @1[I] if element I is the only nonzero + element of @1. */ +(for reduc (IFN_REDUC_PLUS IFN_REDUC_IOR IFN_REDUC_XOR) + (simplify (reduc (view_convert? (bit_and @0 VECTOR_CST@1))) + (with { int i = single_nonzero_element (@1); } + (if (i >= 0) + (with { tree elt = vector_cst_elt (@1, i); + tree elt_type = TREE_TYPE (elt); + unsigned int elt_bits = tree_to_uhwi (TYPE_SIZE (elt_type)); + tree size = bitsize_int (elt_bits); + tree pos = bitsize_int (elt_bits * i); } + (view_convert + (bit_and:elt_type + (BIT_FIELD_REF:elt_type @0 { size; } { pos; }) + { elt; }))))))) Index: gcc/testsuite/gcc.dg/vect/pr88598-1.c =================================================================== --- /dev/null 2018-12-31 11:20:29.178325188 +0000 +++ gcc/testsuite/gcc.dg/vect/pr88598-1.c 2019-01-04 11:40:36.577654458 +0000 @@ -0,0 +1,55 @@ +/* { dg-do run } */ +/* { dg-additional-options "-fdump-tree-optimized" } */ + +#include "tree-vect.h" + +#define N 4 + +int a[N]; + +int __attribute__ ((noipa)) +f1 (void) +{ + int b[N] = { 15, 0, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] & b[i]; + return res; +} + +int __attribute__ ((noipa)) +f2 (void) +{ + int b[N] = { 0, 31, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] & b[i]; + return res; +} + +int __attribute__ ((noipa)) +f3 (void) +{ + int b[N] = { 0, 0, 0, -1 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] & b[i]; + return res; +} + +int +main () +{ + check_vect (); + + for (int i = 0; i < N; ++i) + a[i] = 0xe0 + i; + + if (f1 () != (a[0] & 15) + || f2 () != (a[1] & 31) + || f3 () != a[N - 1]) + __builtin_abort (); + + return 0; +} + +/* ??? We need more constant folding for this to work with fully-masked + loops. */ +/* { dg-final { scan-tree-dump-not {REDUC_PLUS} "optimized" { xfail aarch64_sve } } } */ Index: gcc/testsuite/gcc.dg/vect/pr88598-2.c =================================================================== --- /dev/null 2018-12-31 11:20:29.178325188 +0000 +++ gcc/testsuite/gcc.dg/vect/pr88598-2.c 2019-01-04 11:40:36.577654458 +0000 @@ -0,0 +1,55 @@ +/* { dg-do run } */ +/* { dg-additional-options "-fdump-tree-optimized" } */ + +#include "tree-vect.h" + +#define N 4 + +int a[N]; + +int __attribute__ ((noipa)) +f1 (void) +{ + int b[N] = { 1, 0, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int __attribute__ ((noipa)) +f2 (void) +{ + int b[N] = { 0, 1, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int __attribute__ ((noipa)) +f3 (void) +{ + int b[N] = { 0, 0, 0, 1 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int +main () +{ + check_vect (); + + for (int i = 0; i < N; ++i) + a[i] = 0xe0 + i; + + if (f1 () != a[0] + || f2 () != a[1] + || f3 () != a[N - 1]) + __builtin_abort (); + + return 0; +} + +/* ??? We need more constant folding for this to work with fully-masked + loops. */ +/* { dg-final { scan-tree-dump-not {REDUC_PLUS} "optimized" { xfail aarch64_sve } } } */ Index: gcc/testsuite/gcc.dg/vect/pr88598-3.c =================================================================== --- /dev/null 2018-12-31 11:20:29.178325188 +0000 +++ gcc/testsuite/gcc.dg/vect/pr88598-3.c 2019-01-04 11:40:36.577654458 +0000 @@ -0,0 +1,55 @@ +/* { dg-do run } */ +/* { dg-additional-options "-ffast-math -fdump-tree-optimized" } */ + +#include "tree-vect.h" + +#define N 4 + +float a[N]; + +float __attribute__ ((noipa)) +f1 (void) +{ + float b[N] = { 1, 0, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +float __attribute__ ((noipa)) +f2 (void) +{ + float b[N] = { 0, 1, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +float __attribute__ ((noipa)) +f3 (void) +{ + float b[N] = { 0, 0, 0, 1 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int +main () +{ + check_vect (); + + for (int i = 0; i < N; ++i) + a[i] = 0xe0 + i; + + if (f1 () != a[0] + || f2 () != a[1] + || f3 () != a[N - 1]) + __builtin_abort (); + + return 0; +} + +/* ??? We need more constant folding for this to work with fully-masked + loops. */ +/* { dg-final { scan-tree-dump-not {REDUC_PLUS} "optimized" { xfail aarch64_sve } } } */ Index: gcc/testsuite/gcc.dg/vect/pr88598-4.c =================================================================== --- /dev/null 2018-12-31 11:20:29.178325188 +0000 +++ gcc/testsuite/gcc.dg/vect/pr88598-4.c 2019-01-04 11:40:36.577654458 +0000 @@ -0,0 +1,51 @@ +/* { dg-do run } */ +/* { dg-additional-options "-fdump-tree-optimized" } */ + +#include "tree-vect.h" + +#define N 4 + +int a[N]; + +int __attribute__ ((noipa)) +f1 (void) +{ + int b[N] = { 0, 15, 15, 15 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] & b[i]; + return res; +} + +int __attribute__ ((noipa)) +f2 (void) +{ + int b[N] = { 0, 31, 0, 31 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] & b[i]; + return res; +} + +int __attribute__ ((noipa)) +f3 (void) +{ + int b[N] = { -1, -1, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] & b[i]; + return res; +} + +int +main () +{ + check_vect (); + + for (int i = 0; i < N; ++i) + a[i] = 0xe0 + i; + + if (f1 () != (a[1] & 15) + (a[2] & 15) + (a[3] & 15) + || f2 () != (a[1] & 31) + (a[3] & 31) + || f3 () != a[0] + a[1]) + __builtin_abort (); + + return 0; +} Index: gcc/testsuite/gcc.dg/vect/pr88598-5.c =================================================================== --- /dev/null 2018-12-31 11:20:29.178325188 +0000 +++ gcc/testsuite/gcc.dg/vect/pr88598-5.c 2019-01-04 11:40:36.577654458 +0000 @@ -0,0 +1,51 @@ +/* { dg-do run } */ +/* { dg-additional-options "-fdump-tree-optimized" } */ + +#include "tree-vect.h" + +#define N 4 + +int a[N]; + +int __attribute__ ((noipa)) +f1 (void) +{ + int b[N] = { 0, 1, 1, 1 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int __attribute__ ((noipa)) +f2 (void) +{ + int b[N] = { 0, 1, 0, 1 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int __attribute__ ((noipa)) +f3 (void) +{ + int b[N] = { 1, 1, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int +main () +{ + check_vect (); + + for (int i = 0; i < N; ++i) + a[i] = 0xe0 + i; + + if (f1 () != a[1] + a[2] + a[3] + || f2 () != a[1] + a[3] + || f3 () != a[0] + a[1]) + __builtin_abort (); + + return 0; +} Index: gcc/testsuite/gcc.dg/vect/pr88598-6.c =================================================================== --- /dev/null 2018-12-31 11:20:29.178325188 +0000 +++ gcc/testsuite/gcc.dg/vect/pr88598-6.c 2019-01-04 11:40:36.577654458 +0000 @@ -0,0 +1,51 @@ +/* { dg-do run } */ +/* { dg-additional-options "-ffast-math -fdump-tree-optimized" } */ + +#include "tree-vect.h" + +#define N 4 + +float a[N]; + +float __attribute__ ((noipa)) +f1 (void) +{ + float b[N] = { 0, 1, 1, 1 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +float __attribute__ ((noipa)) +f2 (void) +{ + float b[N] = { 0, 1, 0, 1 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +float __attribute__ ((noipa)) +f3 (void) +{ + float b[N] = { 1, 1, 0, 0 }, res = 0; + for (int i = 0; i < N; ++i) + res += a[i] * b[i]; + return res; +} + +int +main () +{ + check_vect (); + + for (int i = 0; i < N; ++i) + a[i] = 0xe0 + i; + + if (f1 () != a[1] + a[2] + a[3] + || f2 () != a[1] + a[3] + || f3 () != a[0] + a[1]) + __builtin_abort (); + + return 0; +}