I've run into a situation where assign_hard_reg()
decides that there are no registers available. This
results in a memory reference being substituted for a
pseudo-register. There's no check to see if the modified
instruction is valid, which it isn't.
There are a lot of live registers and it is possible
that there are no unused register. assign_hard_reg()
is finding that the cost of using any of the registers
it checks is higher than the cost of a memory reference.
I looked at record_operand_costs() and record_reg_classes().
This is supposed to calculate the cost of using memory
or a hard reg for an insn's operands. Since none of the
constraints permit a memory reference, I would expect that
the mem_cost calculated for each operand would be a high
value; instead it is low. If I force the mem_cost value
to be high, then assign_hard_reg() does assign a register.
record_operand_costs() does initialize op_costs[] to
high values, both for memory and registers. This is
reset in record_reg_classes() to the value from
ira_memory_move_cost[] in the following code:
/* If the alternative actually allows memory, make
things a bit cheaper since we won't need an extra
insn to load it. */
pp->mem_cost
= ((recog_data.operand_type[i] != OP_IN
? ira_memory_move_cost[mode][classes[i]][0] : 0)
+ (recog_data.operand_type[i] != OP_OUT
? ira_memory_move_cost[mode][classes[i]][1] : 0)
- allows_mem[i]) * frequency;
The alternative doesn't allow memory, so I'm unclear why
mem_cost is being set. allows_mem[] is zero for all
operands in the insn.
Can anyone give me some guidance here?
--
Michael Eager ea...@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306 650-325-8077
