This is the mail archive of the
mailing list for the GCC project.
Re: Speedup to propagate_one_insn
- From: law at redhat dot com
- To: Jan Hubicka <jh at suse dot cz>
- Cc: gcc-patches at gcc dot gnu dot org, rth at redhat dot com
- Date: Thu, 05 Feb 2004 11:38:56 -0700
- Subject: Re: Speedup to propagate_one_insn
- Reply-to: law at redhat dot com
In message <20040205163522.GT21096@kam.mff.cuni.cz>, Jan Hubicka writes:
>Bootstrapped/regetsted i686-pc-gnu-linux, OK?
>2004-02-05 Jan Hubicka <firstname.lastname@example.org>
> * recog.c (split_all_insns): Do not update reg info.
> * regrename.c (regrename_optimize): Likewise.
> * toplev.c (rest_of_handle_reorder_blocks): Likewise.
> * flow.c (struct propagate_block_info): Add insn_num field.
> (reg_deaths): New array.
> (life_analysis): Free reg_deaths info.
> (allocate_reg_life_data): Allocate reg_deaths array.
> (propagate_one_insn): Use new array.
> (init_propagate_block): Initialize it.
> (free_propagate_block_info): Finish compuation of REG_LIVE_LENGTH
> (attempt_auto_inc): Sanity check that REG_INFO is not computed
> at same time.
> (mark_used_regs): Update new array.
Funny, I had noticed basically the same thing within the last couple
weeks as I was analyzing a register allocation issues with tree-ssa.
Since ultimately this issue doesn't affect how registers are allocated,
I just noted it and went on with my analysis.
I suspect you didn't mean to include this hunk
>+ /* When PROP_REG_INFO set, array containing information at what
>+ instruction given register died. */
>+ static int *reg_deaths;
So what happens when a register dies more than once in a block?
Oh, I see where that's handled. You might want to add a comment
either to reg_deaths or somewhere in the code which briefly describes
how pbi->num_insn - reg_deaths represents the number of insns
between the most recent death of the register and the current instruction
within the block.
Consider it pre-approved after removal of the cp/tree.c hunk and a
slight update to the comments for the issue noted above.
What I was pondering to fix this problem was to compute n_insns on a
For registers which are live through the block (ie, they never die in the
block) we'd use n_insns. For registers which die in the block we'd
fall back to something like what we do now.
Of course I haven't actually tried to implement it, so I don't know
how feasible my scheme is.
BTW, is the qty comparison function in local/global showing up at all?
There's some obvious lossage in those as well, though it may not be
enough to matter.