Ping?
On Wed, Sep 03, 2014 at 06:51:44AM -0700, Segher Boessenkool wrote:
> This came up when investigating PR62151. In that PR combine messes up a
> four-insn combination. It should really have done the combination of the
> first three insns in that. The second of those instructions sets a register;
> the third clobbers the same. Substituting the source of the set into the
> clobber usually results in invalid RTL so that the combination will not be
> valid; also, it confuses the undobuf machinery. can_combine_p rejects
> the combination for this reason.
>
> But we can simply make subst not substitute into clobbers of registers.
> Any unnecessary clobbers will be removed later anyway.
>
> With this patch, the three-insn combination in PR62151 is successful. It
> does likely not really solve the problem there though, it just hides it.
>
> Bootstrapped and regression checked on powerpc64-linux, options
> -m64,-m32,-m32/-mpowerpc64.
>
> Is this okay for mainline?
>
>
> Segher
>
>
> 2014-09-03 Segher Boessenkool <seg...@kernel.crashing.org>
>
> PR rtl-optimization/62151
> * combine.c (can_combine_p): Allow the destination register of INSN
> to be clobbered in I3.
> (subst): Do not substitute into clobbers of registers.
>
> ---
> gcc/combine.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/gcc/combine.c b/gcc/combine.c
> index 60524b5..6a5dfbb 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -1950,11 +1950,7 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn
> *pred ATTRIBUTE_UNUSED,
> for (i = XVECLEN (PATTERN (i3), 0) - 1; i >= 0; i--)
> if (GET_CODE (XVECEXP (PATTERN (i3), 0, i)) == CLOBBER)
> {
> - /* Don't substitute for a register intended as a clobberable
> - operand. */
> rtx reg = XEXP (XVECEXP (PATTERN (i3), 0, i), 0);
> - if (rtx_equal_p (reg, dest))
> - return 0;
>
> /* If the clobber represents an earlyclobber operand, we must not
> substitute an expression containing the clobbered register.
> @@ -4964,6 +4960,11 @@ subst (rtx x, rtx from, rtx to, int in_dest, int
> in_cond, int unique_copy)
> || (REG_P (X) && REG_P (Y) \
> && REGNO (X) == REGNO (Y) && GET_MODE (X) == GET_MODE (Y)))
>
> + /* Do not substitute into clobbers of regs -- this will never result in
> + valid RTL. */
> + if (GET_CODE (x) == CLOBBER && REG_P (XEXP (x, 0)))
> + return x;
> +
> if (! in_dest && COMBINE_RTX_EQUAL_P (x, from))
> {
> n_occurrences++;
> --
> 1.8.1.4
