Hi, This patch adds const0 move checking for CLEAR_BY_PIECES. The original vec_duplicate handles duplicates of non-constant inputs. But 0 is a constant. So even a platform doesn't support vec_duplicate, it could still do clear by pieces if it supports const0 move by that mode.
Compared to the previous version, the main changes are to create a new class for clear by pieces and add an additional argument to indicate if the object is constant in pieces_addr. https://gcc.gnu.org/pipermail/gcc-patches/2024-July/658337.html I didn't convert const0 move predicate check to an assertion as it caused ICEs on i386. On i386, some modes (V8QI V4HI V2SI V1DI) have move expand defined but their predicates don't include const0. Bootstrapped and tested on powerpc64-linux BE and LE with no regressions. On i386, it got several regressions. One issue is the predicate of V16QI move expand doesn't include const0. Thus V16QI mode can't be used for clear by pieces with the patch. The second issue is the const0 is passed directly to the move expand with the patch. Originally it is forced to a pseudo and i386 can leverage the previous data to do optimization. The patch also raises several regressions on aarch64. The V2x8QImode replaces TImode to do 16-byte clear by pieces as V2x8QImode move expand supports const0 and vector mode is preferable. I drafted a patch to address the issue. It will be sent for review in a separate email. Another problem is V8QImode replaces DImode to do 8-byte clear by pieces. It seems cause different sequences of instructions but the actually instructions are the same. ChangeLog expand: Add const0 move checking for CLEAR_BY_PIECES optabs vec_duplicate handles duplicates of non-constant inputs. The 0 is a constant. So even a platform doesn't support vec_duplicate, it could still do clear by pieces if it supports const0 move. This patch adds the checking. gcc/ * expr.cc (by_pieces_mode_supported_p): Add const0 move checking for CLEAR_BY_PIECES. (pieces_addr::pieces_addr): Add fifth argument is_const to indicate if object is a constant. Do not set m_addr_inc if object is a constant. (op_by_pieces_d::op_by_pieces_d): Initialize m_from by setting is_const to true for CLEAR_BY_PIECES. (class clear_by_pieces_d): New. (clear_by_pieces_d::prepare_mode): New. (clear_by_pieces_d::generate): New. (clear_by_pieces): Replace store_by_pieces_d with clear_by_pieces_d. patch.diff diff --git a/gcc/expr.cc b/gcc/expr.cc index 9f66d479445..abf69c8d698 100644 --- a/gcc/expr.cc +++ b/gcc/expr.cc @@ -1014,14 +1014,20 @@ can_use_qi_vectors (by_pieces_operation op) static bool by_pieces_mode_supported_p (fixed_size_mode mode, by_pieces_operation op) { - if (optab_handler (mov_optab, mode) == CODE_FOR_nothing) + enum insn_code icode = optab_handler (mov_optab, mode); + if (icode == CODE_FOR_nothing) return false; - if ((op == SET_BY_PIECES || op == CLEAR_BY_PIECES) + if (op == SET_BY_PIECES && VECTOR_MODE_P (mode) && optab_handler (vec_duplicate_optab, mode) == CODE_FOR_nothing) return false; + if (op == CLEAR_BY_PIECES + && VECTOR_MODE_P (mode) + && !insn_operand_matches (icode, 1, CONST0_RTX (mode))) + return false; + if (op == COMPARE_BY_PIECES && !can_compare_p (EQ, mode, ccp_jump)) return false; @@ -1184,7 +1190,7 @@ class pieces_addr by_pieces_constfn m_constfn; void *m_cfndata; public: - pieces_addr (rtx, bool, by_pieces_constfn, void *); + pieces_addr (rtx, bool, by_pieces_constfn, void *, bool = false); rtx adjust (fixed_size_mode, HOST_WIDE_INT, by_pieces_prev * = nullptr); void increment_address (HOST_WIDE_INT); void maybe_predec (HOST_WIDE_INT); @@ -1204,7 +1210,7 @@ public: memory load. */ pieces_addr::pieces_addr (rtx obj, bool is_load, by_pieces_constfn constfn, - void *cfndata) + void *cfndata, bool is_const) : m_obj (obj), m_is_load (is_load), m_constfn (constfn), m_cfndata (cfndata) { m_addr_inc = 0; @@ -1228,7 +1234,9 @@ pieces_addr::pieces_addr (rtx obj, bool is_load, by_pieces_constfn constfn, else { m_addr = NULL_RTX; - if (!is_load) + if (is_const) + ; + else if (!is_load) { m_auto = true; if (STACK_GROWS_DOWNWARD) @@ -1391,7 +1399,7 @@ op_by_pieces_d::op_by_pieces_d (unsigned int max_pieces, rtx to, unsigned int align, bool push, by_pieces_operation op) : m_to (to, to_load, NULL, NULL), - m_from (from, from_load, from_cfn, from_cfn_data), + m_from (from, from_load, from_cfn, from_cfn_data, op == CLEAR_BY_PIECES), m_len (len), m_max_size (max_pieces + 1), m_push (push), m_op (op) { @@ -1724,6 +1732,48 @@ store_by_pieces_d::finish_retmode (memop_ret retmode) return m_to.adjust (QImode, m_offset); } +/* Derived class from op_by_pieces_d, providing support for block clear + operations. */ + +class clear_by_pieces_d : public op_by_pieces_d +{ + insn_gen_fn m_gen_fun; + + void generate (rtx, rtx, machine_mode) final override; + bool prepare_mode (machine_mode, unsigned int) final override; + + public: + clear_by_pieces_d (rtx to, unsigned HOST_WIDE_INT len, unsigned int align) + : op_by_pieces_d (STORE_MAX_PIECES, to, false, NULL_RTX, false, NULL, + NULL, len, align, false, CLEAR_BY_PIECES) + { + } +}; + +/* Return true if MODE can be used for a set of stores, given an + alignment ALIGN. Prepare whatever data is necessary for later + calls to generate. */ + +bool +clear_by_pieces_d::prepare_mode (machine_mode mode, unsigned int align) +{ + insn_code icode = optab_handler (mov_optab, mode); + m_gen_fun = GEN_FCN (icode); + return icode != CODE_FOR_nothing && align >= GET_MODE_ALIGNMENT (mode); +} + +/* A callback used when iterating for a clear_by_pieces_operation. + The input op1 should be NULL for clear_by_pieces and set it to + const0 of that mode. */ + +void +clear_by_pieces_d::generate (rtx op0, rtx op1, machine_mode mode) +{ + gcc_assert (!op1); + op1 = CONST0_RTX (mode); + emit_insn (m_gen_fun (op0, op1)); +} + /* Determine whether the LEN bytes generated by CONSTFUN can be stored to memory using several move instructions. CONSTFUNDATA is a pointer which will be passed as argument in every CONSTFUN call. @@ -1849,10 +1899,7 @@ clear_by_pieces (rtx to, unsigned HOST_WIDE_INT len, unsigned int align) if (len == 0) return; - /* Use builtin_memset_read_str to support vector mode broadcast. */ - char c = 0; - store_by_pieces_d data (to, builtin_memset_read_str, &c, len, align, - CLEAR_BY_PIECES); + clear_by_pieces_d data (to, len, align); data.run (); }
