Bernd Schmidt <ber...@codesourcery.com> writes:
> + CLEAR_HARD_REG_SET (set_regs);
> + note_stores (PATTERN (scan), record_hard_reg_sets,
> + &set_regs);
> + if (CALL_P (scan))
> + IOR_HARD_REG_SET (set_regs, call_used_reg_set);
> + for (link = REG_NOTES (scan); link; link = XEXP (link, 1))
> + if (REG_NOTE_KIND (link) == REG_INC)
> + record_hard_reg_sets (XEXP (link, 0), NULL, &set_regs);
> +
> + if (TEST_HARD_REG_BIT (set_regs, srcreg)
> + || reg_referenced_p (SET_DEST (set),
> + PATTERN (scan)))
> + {
> + scan = NULL_RTX;
> + break;
> + }
> + if (CALL_P (scan))
> + {
> + rtx link = CALL_INSN_FUNCTION_USAGE (scan);
> + while (link)
> + {
> + rtx tmp = XEXP (link, 0);
> + if (GET_CODE (tmp) == USE
> + && reg_referenced_p (SET_DEST (set), tmp))
> + break;
> + link = XEXP (link, 1);
> + }
> + if (link)
> + {
> + scan = NULL_RTX;
> + break;
> + }
> + }
Could we use DF_REF_USES/DEFS here instead?
I'd like to get a stage where new code should treat DF_REF_USES/DEFS
as the default way of testing for register usage. I think this sort
of ad-hoc liveness stuff should be a last resort, and should have a
comment saying why DF_REF_USES/DEFS isn't suitable.
Rather than walk all the instructions of intermediate blocks,
you could just test DF_LR_BB_INFO (bb)->use to see whether the
block uses the register at all.
> + FOR_BB_INSNS_SAFE (entry_block, insn, curr)
Is there any particular reason for doing a forward walk rather than
a backward walk? A backward walk would allow chains to be moved,
and would avoid the need for the quadraticness in the current:
for each insn I in bb
for each insn J after I in bb
since you could then keep an up-to-date record of what registers
are used or set by the instructions that you aren't moving.
Also:
+/* Look for sets of call-saved registers in the first block of the
+ function, and move them down into successor blocks if the register
+ is used only on one path. This exposes more opportunities for
+ shrink-wrapping.
+ These kinds of sets often occur when incoming argument registers are
+ moved to call-saved registers because their values are live across
+ one or more calls during the function. */
+
+static void
+prepare_shrink_wrap (basic_block entry_block)
There's no check for call-savedness. Is that deliberate? I'm seeing
a case where we have:
(set (reg 2) (reg 15))
(set (reg 15) (reg 2))
(yes, it's silly, but bear with me) for call-clobbered registers 2 and 15.
We move the second instruction as far as possible, making 2 live for
much longer. So if the prologue uses 2 as a temporary register, this
would actually prevent shrink-wrapping.
The reason I'm suddenly "reviewing" the code now is that it
doesn't prevent shrink-wrapping, because nothing adds register 2
to the liveness info of the affected blocks. The temporary prologue
value of register 2 is then moved into register 15.
Testcase is gcc.c-torture/execute/920428-2.c on mips64-linux-gnu cc1
(although any MIPS should do) with:
-O2 -mabi=32 -mips16 -mno-shared -mabicalls -march=mips32
Richard
