This patch addresses a code quality regression in GCC 12 by implementing some constant folding/simplification transformations for REDUC_PLUS_EXPR in match.pd. The motivating example is gcc.dg/vect/pr89440.c which with -O2 -ffast-math (with vectorization now enabled) gets optimized to:
float f (float x) { vector(4) float vect_x_14.11; vector(4) float _2; float _32; _2 = {x_9(D), 0.0, 0.0, 0.0}; vect_x_14.11_29 = _2 + { 1.0e+1, 2.6e+1, 4.2e+1, 5.8e+1 }; _32 = .REDUC_PLUS (vect_x_14.11_29); [tail call] return _32; } With these proposed new transformations, we can simplify the above code even further. float f (float x) { float _32; _32 = x_9(D) + 1.36e+2; return _32; } [which happens to match what we'd produce with -fno-tree-vectorize, and with GCC 11]. This patch has been tested on x86_64-pc-linux-gnu with make bootstrap and make -k check with no new failures. Ok for mainline? 2022-02-21 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog * fold-const.cc (ctor_single_nonzero_element): New function to return the single non-zero element of a (vector) constructor. * fold-const.h (ctor_single_nonzero_element): Prototype here. * match.pd (reduc (constructor@0)): Simplify reductions of a constructor containing a single non-zero element. (reduc (@0 op VECTOR_CST) -> (reduc @0) op CONST): Simplify reductions of vector operations of the same operator with constant vector operands. gcc/testsuite/ChangeLog * gcc.dg/fold-reduc-1.c: New test case. Thanks in advance, Roger --
diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index 386d573..4283308 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -16792,6 +16792,33 @@ address_compare (tree_code code, tree type, tree op0, tree op1, return equal; } +/* Return the single non-zero element of a CONSTRUCTOR or NULL_TREE. */ +tree +ctor_single_nonzero_element (const_tree t) +{ + unsigned HOST_WIDE_INT idx; + constructor_elt *ce; + tree elt = NULL_TREE; + + if (TREE_CODE (t) == SSA_NAME) + { + gassign *def = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (t)); + if (gimple_assign_rhs_code (def) == CONSTRUCTOR) + t = gimple_assign_rhs1 (def); + } + + if (TREE_CODE (t) != CONSTRUCTOR) + return NULL_TREE; + for (idx = 0; vec_safe_iterate (CONSTRUCTOR_ELTS (t), idx, &ce); idx++) + if (!integer_zerop (ce->value) && !real_zerop (ce->value)) + { + if (elt) + return NULL_TREE; + elt = ce->value; + } + return elt; +} + #if CHECKING_P namespace selftest { diff --git a/gcc/fold-const.h b/gcc/fold-const.h index f217598..b2f0a2f 100644 --- a/gcc/fold-const.h +++ b/gcc/fold-const.h @@ -224,6 +224,7 @@ extern const char *c_getstr (tree); extern wide_int tree_nonzero_bits (const_tree); extern int address_compare (tree_code, tree, tree, tree, tree &, tree &, poly_int64 &, poly_int64 &, bool); +extern tree ctor_single_nonzero_element (const_tree); /* Return OFF converted to a pointer offset type suitable as offset for POINTER_PLUS_EXPR. Use location LOC for this conversion. */ diff --git a/gcc/match.pd b/gcc/match.pd index d9d8359..047fb50 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -7528,6 +7528,20 @@ and, (BIT_FIELD_REF:elt_type @0 { size; } { pos; }) { elt; }))))))) +/* Fold reduction of a single nonzero element constructor. */ +(for reduc (IFN_REDUC_PLUS IFN_REDUC_IOR IFN_REDUC_XOR) + (simplify (reduc (CONSTRUCTOR@0)) + (with { tree elt = ctor_single_nonzero_element (@0); } + (if (elt) + (non_lvalue { elt; }))))) + +/* Fold REDUC (@0 op VECTOR_CST) as REDUC (@0) op REDUC (VECTOR_CST). */ +(for reduc (IFN_REDUC_PLUS IFN_REDUC_MAX IFN_REDUC_MIN IFN_REDUC_FMAX + IFN_REDUC_FMIN IFN_REDUC_AND IFN_REDUC_IOR IFN_REDUC_XOR) + op (plus max min IFN_FMAX IFN_FMIN bit_and bit_ior bit_xor) + (simplify (reduc (op @0 VECTOR_CST@1)) + (op (reduc:type @0) (reduc:type @1)))) + (simplify (vec_perm @0 @1 VECTOR_CST@2) (with diff --git a/gcc/testsuite/gcc.dg/fold-reduc-1.c b/gcc/testsuite/gcc.dg/fold-reduc-1.c new file mode 100644 index 0000000..c8360b0 --- /dev/null +++ b/gcc/testsuite/gcc.dg/fold-reduc-1.c @@ -0,0 +1,19 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -ffast-math -fdump-tree-optimized" } */ +float foo (float x) +{ + int i; + float j; + float a = 0; + for (i = 0; i < 4; ++i) + { + for (j = 0; j < 4; ++j) + { + a += 1; + x += a; + } + } + return x; +} + +/* { dg-final { scan-tree-dump-not "REDUC_PLUS" "optimized"} } */