According to PR: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110751
As Richard and Richi suggested, we recognize uninitialized SSA_NAME and convert it into SCRATCH rtx if the target predicate allows SCRATCH. It can help to reduce redundant data move instructions of targets like RISC-V. gcc/ChangeLog: * internal-fn.cc (expand_fn_using_insn): Support undefined rtx. * optabs.cc (maybe_legitimize_operand): Ditto. (can_reuse_operands_p): Ditto. * optabs.h (enum expand_operand_type): Ditto. (create_undefined_input_operand): Ditto. --- gcc/internal-fn.cc | 4 ++++ gcc/optabs.cc | 16 ++++++++++++++++ gcc/optabs.h | 14 +++++++++++++- 3 files changed, 33 insertions(+), 1 deletion(-) diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc index 0fd34359247..61d5a9e4772 100644 --- a/gcc/internal-fn.cc +++ b/gcc/internal-fn.cc @@ -247,6 +247,10 @@ expand_fn_using_insn (gcall *stmt, insn_code icode, unsigned int noutputs, create_convert_operand_from (&ops[opno], rhs_rtx, TYPE_MODE (rhs_type), TYPE_UNSIGNED (rhs_type)); + else if (TREE_CODE (rhs) == SSA_NAME + && SSA_NAME_IS_DEFAULT_DEF (rhs) + && VAR_P (SSA_NAME_VAR (rhs))) + create_undefined_input_operand (&ops[opno], TYPE_MODE (rhs_type)); else create_input_operand (&ops[opno], rhs_rtx, TYPE_MODE (rhs_type)); opno += 1; diff --git a/gcc/optabs.cc b/gcc/optabs.cc index 32ff379ffc3..d8c771547a3 100644 --- a/gcc/optabs.cc +++ b/gcc/optabs.cc @@ -8102,6 +8102,21 @@ maybe_legitimize_operand (enum insn_code icode, unsigned int opno, goto input; } break; + + case EXPAND_UNDEFINED: + { + mode = insn_data[(int) icode].operand[opno].mode; + rtx scratch = gen_rtx_SCRATCH (mode); + /* For SCRATCH rtx which is converted from uninitialized + SSA, we convert it as fresh pseudo when target doesn't + allow scratch rtx in predicate. Otherwise, return true. */ + if (!insn_operand_matches (icode, opno, scratch)) + { + op->value = gen_reg_rtx (mode); + goto input; + } + return true; + } } return insn_operand_matches (icode, opno, op->value); } @@ -8147,6 +8162,7 @@ can_reuse_operands_p (enum insn_code icode, case EXPAND_INPUT: case EXPAND_ADDRESS: case EXPAND_INTEGER: + case EXPAND_UNDEFINED: return true; case EXPAND_CONVERT_TO: diff --git a/gcc/optabs.h b/gcc/optabs.h index c80b7f4dc1b..4eb1f9ee09a 100644 --- a/gcc/optabs.h +++ b/gcc/optabs.h @@ -37,7 +37,8 @@ enum expand_operand_type { EXPAND_CONVERT_TO, EXPAND_CONVERT_FROM, EXPAND_ADDRESS, - EXPAND_INTEGER + EXPAND_INTEGER, + EXPAND_UNDEFINED }; /* Information about an operand for instruction expansion. */ @@ -117,6 +118,17 @@ create_input_operand (class expand_operand *op, rtx value, create_expand_operand (op, EXPAND_INPUT, value, mode, false); } +/* Make OP describe an undefined input operand for uninitialized + SSA. It's the scratch operand with mode MODE; MODE cannot be + VOIDmode. */ + +inline void +create_undefined_input_operand (class expand_operand *op, machine_mode mode) +{ + create_expand_operand (op, EXPAND_UNDEFINED, gen_rtx_SCRATCH (mode), mode, + false); +} + /* Like create_input_operand, except that VALUE must first be converted to mode MODE. UNSIGNED_P says whether VALUE is unsigned. */ -- 2.36.3