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.
Bootstrap and Regression on x86 passed.
gcc/ChangeLog:
* internal-fn.cc (expand_fn_using_insn): Support undefined rtx value.
* 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 | 13 ++++++++++++-
gcc/optabs.h | 13 ++++++++++++-
3 files changed, 28 insertions(+), 2 deletions(-)
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..8b96f23aec0 100644
--- a/gcc/optabs.cc
+++ b/gcc/optabs.cc
@@ -8102,6 +8102,16 @@ maybe_legitimize_operand (enum insn_code icode, unsigned
int opno,
goto input;
}
break;
+
+ case EXPAND_UNDEFINED_INPUT:
+ /* See if the predicate accepts a SCRATCH rtx, which in this context
+ indicates an undefined value. Use an uninitialized register if not. */
+ if (!insn_operand_matches (icode, opno, op->value))
+ {
+ op->value = gen_reg_rtx (op->mode);
+ goto input;
+ }
+ return true;
}
return insn_operand_matches (icode, opno, op->value);
}
@@ -8140,7 +8150,8 @@ can_reuse_operands_p (enum insn_code icode,
switch (op1->type)
{
case EXPAND_OUTPUT:
- /* Outputs must remain distinct. */
+ case EXPAND_UNDEFINED_INPUT:
+ /* Outputs and undefined intputs must remain distinct. */
return false;
case EXPAND_FIXED:
diff --git a/gcc/optabs.h b/gcc/optabs.h
index c80b7f4dc1b..9b78d40a46c 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_INPUT
};
/* Information about an operand for instruction expansion. */
@@ -117,6 +118,16 @@ 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 of mode MODE. MODE cannot
+ be null. */
+
+inline void
+create_undefined_input_operand (class expand_operand *op, machine_mode mode)
+{
+ create_expand_operand (op, EXPAND_UNDEFINED_INPUT, 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
