> -----Original Message----- > From: Segher Boessenkool [mailto:seg...@kernel.crashing.org] > Sent: Friday, February 13, 2015 6:16 AM > To: Hale Wang; 'GCC Patches'; Richard Sandiford > Subject: Re: Ping : [PATCH] [gcc, combine] PR46164: Don't combine the insns > if a volatile register is contained. > > On Thu, Feb 12, 2015 at 03:54:21PM +0000, Richard Sandiford wrote: > > "Hale Wang" <hale.w...@arm.com> writes: > > > Ping? > > It's not a regression (or is it?), so it is not appropriate for stage4. > > > > >> diff --git a/gcc/combine.c b/gcc/combine.c index 5c763b4..6901ac2 > > >> 100644 > > >> --- a/gcc/combine.c > > >> +++ b/gcc/combine.c > > >> @@ -1904,6 +1904,12 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, > > >> rtx_insn *pred ATTRIBUTE_UNUSED, > > >> set = expand_field_assignment (set); > > >> src = SET_SRC (set), dest = SET_DEST (set); > > >> > > >> + /* Don't combine if dest contains a user specified register, > > >> + because > > > the > > >> + user specified register (same with dest) in i3 would be > > >> + replaced by > > > the > > >> + src of insn which might be different with the user's expectation. > > >> + */ if (REG_P (dest) && REG_USERVAR_P (dest) && > HARD_REGISTER_P > > >> (dest)) > > >> + return 0; > > > > I suppose this is similar to Andrew's comment, but I think the rule is > > that it's invalid to replace a REG_USERVAR_P operand in an inline asm. > > Why not? You probably mean register asm, not all user variables? > > > Outside of an inline asm we make no guarantee about whether something > > is stored in a particular register or not. > > > > So IMO we should be checking whether either INSN or I3 is an asm as > > well as the above. > > [ INSN can never be an asm, that is already refused by can_combine_p. ] >
Indeed. If INSN is an asm operand, it's already refused by can_combine_p. Hale. > We do not guarantee things will end up in the specified reg (except for asm), > but will it hurt to leave things in the reg the user said it should be in, even if > we do not guarantee this behaviour? > > > Segher
