On 05/19/2014 07:30 AM, Tom de Vries wrote:
> + for (insn = get_insns (); insn != NULL_RTX; insn = next_insn (insn))
> + {
> + HARD_REG_SET insn_used_regs;
> +
> + if (!NONDEBUG_INSN_P (insn))
> + continue;
> +
> + find_all_hard_reg_sets (insn, &insn_used_regs, false);
> +
> + if (CALL_P (insn)
> + && !get_call_reg_set_usage (insn, &insn_used_regs, call_used_reg_set))
> + {
> + CLEAR_HARD_REG_SET (node->function_used_regs);
> + return;
> + }
> +
> + IOR_HARD_REG_SET (node->function_used_regs, insn_used_regs);
> + }
As an aside, wouldn't it work out better if we collect into a local variable
instead of writing to memory here in node->function_used_regs each time? But
not the main point...
Let's suppose that we've got a rather large function, with only local calls for
which we can acquire usage. Let's suppose that even one of those callees
further calls something else, such that insn_used_regs == call_used_reg_set.
We fill node->function_used_regs immediately, but keep scanning the rest of the
large function.
> +
> + /* Be conservative - mark fixed and global registers as used. */
> + IOR_HARD_REG_SET (node->function_used_regs, fixed_reg_set);
> + for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
> + if (global_regs[i])
> + SET_HARD_REG_BIT (node->function_used_regs, i);
> +
> +#ifdef STACK_REGS
> + /* Handle STACK_REGS conservatively, since the df-framework does not
> + provide accurate information for them. */
> +
> + for (i = FIRST_STACK_REG; i <= LAST_STACK_REG; i++)
> + SET_HARD_REG_BIT (node->function_used_regs, i);
> +#endif
> +
> + node->function_used_regs_valid = 1;
Wouldn't it be better to compare the collected function_used_regs; if it
contains all of call_used_reg_set, decline to set function_used_regs_valid.
That way, we'll early exit from the above loop whenever we see that we can't
improve over the default call-clobber set.
Although perhaps function_used_regs_valid is no longer the best name in that
case...
r~
