On 18/04/13 06:34, Bin Cheng wrote:
> Hi,
> Before thumb1_reorg, ARM backend uses peephole to save comparison
> instructions when a flag setting move is found before branch instruction.
> Since we are using thumb1_reog now, it can be extended to catch more
> opportunities by searching flag setting move instruction before branch,
> rather than only the exact one before branch.
> For example:
>
> mov r0, r1
> //other insns does not kill r0
> branch if (r0 == 0)
> //other insns
>
> Tested on thumb1, is it OK?
>
>
> 2013-04-18 Bin Cheng <bin.ch...@arm.com>
>
> * config/arm/arm.c (thumb1_reorg): Search for flag setting insn
> before branch in same basic block. Check both src and dest of
> the move insn.
>
>
Sorry for the delay, I've been trying to get my head around this one.
> thumb1_reorg-20130417.txt
>
>
> Index: gcc/config/arm/arm.c
> ===================================================================
> --- gcc/config/arm/arm.c (revision 197562)
> +++ gcc/config/arm/arm.c (working copy)
> @@ -14026,6 +14026,7 @@ thumb1_reorg (void)
> rtx set, dest, src;
> rtx pat, op0;
> rtx prev, insn = BB_END (bb);
> + bool insn_clobbered = false;
>
> while (insn != BB_HEAD (bb) && DEBUG_INSN_P (insn))
> insn = PREV_INSN (insn);
> @@ -14034,12 +14035,29 @@ thumb1_reorg (void)
> if (INSN_CODE (insn) != CODE_FOR_cbranchsi4_insn)
> continue;
>
> - /* Find the first non-note insn before INSN in basic block BB. */
> + /* Get the register with which we are comparing. */
> + pat = PATTERN (insn);
> + op0 = XEXP (XEXP (SET_SRC (pat), 0), 0);
> +
> + /* Find the first flag setting insn before INSN in basic block BB. */
> gcc_assert (insn != BB_HEAD (bb));
> - prev = PREV_INSN (insn);
> - while (prev != BB_HEAD (bb) && (NOTE_P (prev) || DEBUG_INSN_P (prev)))
> - prev = PREV_INSN (prev);
> + for (prev = PREV_INSN (insn);
> + (!insn_clobbered
> + && prev != BB_HEAD (bb)
> + && (NOTE_P (prev)
> + || DEBUG_INSN_P (prev)
> + || (GET_CODE (prev) == SET
This can't be right. prev is an insn of some form, so the test that it
is a SET will always fail.
What you need to do here is to initialize 'set' to null before the loop
and then have something like
|| ((set = single_set (prev)) != NULL
> + && get_attr_conds (prev) == CONDS_NOCOND)));
> + prev = PREV_INSN (prev))
> + {
> + if (reg_set_p (op0, prev))
> + insn_clobbered = true;
> + }
>
> + /* Skip if op0 is clobbered by insn other than prev. */
> + if (insn_clobbered)
> + continue;
> +
> set = single_set (prev);
This now becomes redundant and ...
> if (!set)
> continue;
This will be based on the set you extracted above.
> @@ -14050,12 +14068,9 @@ thumb1_reorg (void)
> || !low_register_operand (src, SImode))
> continue;
>
> - pat = PATTERN (insn);
> - op0 = XEXP (XEXP (SET_SRC (pat), 0), 0);
> /* Rewrite move into subtract of 0 if its operand is compared with ZERO
> - in INSN. Don't need to check dest since cprop_hardreg pass propagates
> - src into INSN. */
> - if (REGNO (op0) == REGNO (src))
> + in INSN. Both src and dest of the move insn are checked. */
> + if (REGNO (op0) == REGNO (src) || REGNO (op0) == REGNO (dest))
> {
> dest = copy_rtx (dest);
> src = copy_rtx (src);
>
R.
