On Tue, 25 Jun 2019 at 20:05, Richard Sandiford
<[email protected]> wrote:
>
> Prathamesh Kulkarni <[email protected]> writes:
> > On Mon, 24 Jun 2019 at 21:41, Prathamesh Kulkarni
> > <[email protected]> wrote:
> >>
> >> On Mon, 24 Jun 2019 at 19:51, Richard Sandiford
> >> <[email protected]> wrote:
> >> >
> >> > Prathamesh Kulkarni <[email protected]> writes:
> >> > > @@ -1415,6 +1460,19 @@ forward_propagate_into (df_ref use)
> >> > > if (!def_set)
> >> > > return false;
> >> > >
> >> > > + if (reg_prop_only
> >> > > + && !REG_P (SET_SRC (def_set))
> >> > > + && !REG_P (SET_DEST (def_set)))
> >> > > + return false;
> >> >
> >> > This should be:
> >> >
> >> > if (reg_prop_only
> >> > && (!REG_P (SET_SRC (def_set)) || !REG_P (SET_DEST (def_set))))
> >> > return false;
> >> >
> >> > so that we return false if either operand isn't a register.
> >> Oops, sorry about that -:(
> >> >
> >> > > +
> >> > > + /* Allow propagations into a loop only for reg-to-reg copies, since
> >> > > + replacing one register by another shouldn't increase the cost.
> >> > > */
> >> > > +
> >> > > + if (DF_REF_BB (def)->loop_father != DF_REF_BB (use)->loop_father
> >> > > + && !REG_P (SET_SRC (def_set))
> >> > > + && !REG_P (SET_DEST (def_set)))
> >> > > + return false;
> >> >
> >> > Same here.
> >> >
> >> > OK with that change, thanks.
> >> Thanks for the review, will make the changes and commit the patch
> >> after re-testing.
> > Hi,
> > Testing the patch showed following failures on 32-bit x86:
> >
> > Executed from: g++.target/i386/i386.exp
> > g++:g++.target/i386/pr88152.C scan-assembler-not vpcmpgt|vpcmpeq|vpsra
> > Executed from: gcc.target/i386/i386.exp
> > gcc:gcc.target/i386/pr66768.c scan-assembler add*.[ \t]%gs:
> > gcc:gcc.target/i386/pr90178.c scan-assembler-times xorl[\\t
> > ]*\\%eax,[\\t ]*%eax 1
> >
> > The failure of pr88152.C is also seen on x86_64.
> >
> > For pr66768.c, and pr90178.c, forwprop replaces register which is
> > volatile and frame related respectively.
> > To avoid that, the attached patch, makes a stronger constraint that
> > src and dest should be a register
> > and not have frame_related or volatil flags set, which is checked in
> > usable_reg_p().
> > Which avoids the failures for both the cases.
> > Does it look OK ?
>
> That's not the reason it's a bad transform. In both cases we're
> propagating r2 <- r1 even though
>
> (a) r1 dies in the copy and
> (b) fwprop can't replace all uses of r2, because some have multiple
> definitions
>
> This has the effect of making both values live in cases where only one
> was previously.
>
> In the case of pr66768.c, fwprop2 is undoing the effect of
> cse.c:canon_reg, which tries to pick the best register to use
> (see cse.c:make_regs_eqv). fwprop1 makes the same change,
> and made it even before the patch, but the cse.c choice should win.
>
> A (hopefully) conservative fix would be to propagate the copy only if
> both registers have a single definition, which you can test with:
>
> (DF_REG_DEF_COUNT (regno) == 1
> && !bitmap_bit_p (DF_LR_OUT (ENTRY_BLOCK_PTR_FOR_FN (m_fn)), regno))
>
> In that case, fwprop should see all uses of the destination, and should
> be able to replace it in all cases with the source.
Ah I see, thanks for the explanation!
The above check works to resolve the failure.
IIUC, !bitmap_bit_p (...) above checks that reg isn't used uninitialized ?
>
> > For g++.target/i386/pr88152.C, the issue is that after the patch,
> > forwprop1 does following propagation (in f10) which wasn't done
> > before:
> >
> > In insn 10, replacing
> > (unspec:SI [
> > (reg:V2DF 91)
> > ] UNSPEC_MOVMSK)
> > with (unspec:SI [
> > (subreg:V2DF (reg:V2DI 90) 0)
> > ] UNSPEC_MOVMSK)
> >
> > This later defeats combine because insn 9 gets deleted.
> > Without patch, the following combination takes place:
> >
> > Trying 7 -> 9:
> > 7: r90:V2DI=r89:V2DI>r93:V2DI
> > REG_DEAD r93:V2DI
> > REG_DEAD r89:V2DI
> > 9: r91:V2DF=r90:V2DI#0
> > REG_DEAD r90:V2DI
> > Successfully matched this instruction:
> > (set (subreg:V2DI (reg:V2DF 91) 0)
> > (gt:V2DI (reg:V2DI 89)
> > (reg:V2DI 93)))
> > allowing combination of insns 7 and 9
> >
> > and then:
> > Trying 6, 9 -> 10:
> > 6: r89:V2DI=const_vector
> > 9: r91:V2DF#0=r89:V2DI>r93:V2DI
> > REG_DEAD r89:V2DI
> > REG_DEAD r93:V2DI
> > 10: r87:SI=unspec[r91:V2DF] 43
> > REG_DEAD r91:V2DF
> > Successfully matched this instruction:
> > (set (reg:SI 87)
> > (unspec:SI [
> > (lt:V2DF (reg:V2DI 93)
> > (const_vector:V2DI [
> > (const_int 0 [0]) repeated x2
> > ]))
> > ] UNSPEC_MOVMSK))
>
> Eh? lt:*V2DF*? Does that mean that it's 0 for false and an all-1 NaN
> for true?
Well looking at .optimized dump:
vector(2) long int _2;
vector(2) double _3;
int _6;
signed long _7;
long int _8;
signed long _9;
long int _10;
<bb 2> [local count: 1073741824]:
_7 = BIT_FIELD_REF <a_4(D), 64, 0>;
_8 = _7 < 0 ? -1 : 0;
_9 = BIT_FIELD_REF <a_4(D), 64, 64>;
_10 = _9 < 0 ? -1 : 0;
_2 = {_8, _10};
_3 = VIEW_CONVERT_EXPR<__m128d>(_2);
_6 = __builtin_ia32_movmskpd (_3); [tail call]
return _6;
So AFAIU, we're using -1 for representing true and 0 for false
and casting -1 (literally) to double would change it's value to -NaN ?
The above insn 10 created by combine is then transformed to following insn 22:
(insn 22 9 16 2 (set (reg:SI 0 ax [87])
(unspec:SI [
(reg:V2DF 20 xmm0 [93])
] UNSPEC_MOVMSK))
"../../stage1-build/gcc/include/emmintrin.h":958:34 4222
{sse2_movmskpd}
(nil))
deleting insn 10.
Thanks,
Prathamesh
>
> Looks like a bug that we manage to fold to that, and manage to match it.
>
> Thanks,
> Richard
>
> > allowing combination of insns 6, 9 and 10
> > original costs 4 + 8 + 4 = 16
> > replacement cost 12
> > deferring deletion of insn with uid = 9.
> > deferring deletion of insn with uid = 6.
> > which deletes insns 2, 3, 6, 7, 9.
> >
> > With patch, it fails to combine 7->10:
> > Trying 7 -> 10:
> > 7: r90:V2DI=r89:V2DI>r93:V2DI
> > REG_DEAD r93:V2DI
> > REG_DEAD r89:V2DI
> > 10: r87:SI=unspec[r90:V2DI#0] 43
> > REG_DEAD r90:V2DI
> > Failed to match this instruction:
> > (set (reg:SI 87)
> > (unspec:SI [
> > (subreg:V2DF (gt:V2DI (reg:V2DI 89)
> > (reg:V2DI 93)) 0)
> > ] UNSPEC_MOVMSK))
> >
> > and subsequently 6, 7 -> 10
> > (attached combine dumps before and after patch).
> >
> > So IIUC, the issue is that the target does not have a pattern that can
> > match the above insn ?
> > I tried a simple workaround to "pessimize" the else condition in
> > propagate_rtx_1 in patch, to require old_rtx and new_rtx have same
> > rtx_code, which at least
> > works for this test-case, but not sure if that's the correct approach.
> > Could you suggest how to proceed ?
> >
> > Thanks,
> > Prathamesh
> >>
> >> Thanks,
> >> Prathamesh
> >> >
> >> > Richard
diff --git a/gcc/fwprop.c b/gcc/fwprop.c
index 45703fe5f01..49e9023a4db 100644
--- a/gcc/fwprop.c
+++ b/gcc/fwprop.c
@@ -448,6 +448,18 @@ enum {
PR_OPTIMIZE_FOR_SPEED = 4
};
+/* Check that X has a single def. */
+
+static bool
+reg_single_def_p (rtx x)
+{
+ if (!REG_P (x))
+ return false;
+
+ int regno = REGNO (x);
+ return (DF_REG_DEF_COUNT (regno) == 1
+ && !bitmap_bit_p (DF_LR_OUT (ENTRY_BLOCK_PTR_FOR_FN (cfun)), regno));
+}
/* Replace all occurrences of OLD in *PX with NEW and try to simplify the
resulting expression. Replace *PX with a new RTL expression if an
@@ -547,6 +559,54 @@ propagate_rtx_1 (rtx *px, rtx old_rtx, rtx new_rtx, int flags)
tem = simplify_gen_subreg (mode, op0, GET_MODE (SUBREG_REG (x)),
SUBREG_BYTE (x));
}
+
+ else
+ {
+ rtvec vec;
+ rtvec newvec;
+ const char *fmt = GET_RTX_FORMAT (code);
+ rtx op;
+
+ for (int i = 0; fmt[i]; i++)
+ switch (fmt[i])
+ {
+ case 'E':
+ vec = XVEC (x, i);
+ newvec = vec;
+ for (int j = 0; j < GET_NUM_ELEM (vec); j++)
+ {
+ op = RTVEC_ELT (vec, j);
+ valid_ops &= propagate_rtx_1 (&op, old_rtx, new_rtx, flags);
+ if (op != RTVEC_ELT (vec, j))
+ {
+ if (newvec == vec)
+ {
+ newvec = shallow_copy_rtvec (vec);
+ if (!tem)
+ tem = shallow_copy_rtx (x);
+ XVEC (tem, i) = newvec;
+ }
+ RTVEC_ELT (newvec, j) = op;
+ }
+ }
+ break;
+
+ case 'e':
+ if (XEXP (x, i))
+ {
+ op = XEXP (x, i);
+ valid_ops &= propagate_rtx_1 (&op, old_rtx, new_rtx, flags);
+ if (op != XEXP (x, i))
+ {
+ if (!tem)
+ tem = shallow_copy_rtx (x);
+ XEXP (tem, i) = op;
+ }
+ }
+ break;
+ }
+ }
+
break;
case RTX_OBJ:
@@ -1370,10 +1430,11 @@ forward_propagate_and_simplify (df_ref use, rtx_insn *def_insn, rtx def_set)
/* Given a use USE of an insn, if it has a single reaching
definition, try to forward propagate it into that insn.
- Return true if cfg cleanup will be needed. */
+ Return true if cfg cleanup will be needed.
+ REG_PROP_ONLY is true if we should only propagate register copies. */
static bool
-forward_propagate_into (df_ref use)
+forward_propagate_into (df_ref use, bool reg_prop_only = false)
{
df_ref def;
rtx_insn *def_insn, *use_insn;
@@ -1394,10 +1455,6 @@ forward_propagate_into (df_ref use)
if (DF_REF_IS_ARTIFICIAL (def))
return false;
- /* Do not propagate loop invariant definitions inside the loop. */
- if (DF_REF_BB (def)->loop_father != DF_REF_BB (use)->loop_father)
- return false;
-
/* Check if the use is still present in the insn! */
use_insn = DF_REF_INSN (use);
if (DF_REF_FLAGS (use) & DF_REF_IN_NOTE)
@@ -1415,6 +1472,19 @@ forward_propagate_into (df_ref use)
if (!def_set)
return false;
+ if (reg_prop_only
+ && (!reg_single_def_p (SET_SRC (def_set))
+ || !reg_single_def_p (SET_DEST (def_set))))
+ return false;
+
+ /* Allow propagations into a loop only for reg-to-reg copies, since
+ replacing one register by another shouldn't increase the cost. */
+
+ if (DF_REF_BB (def)->loop_father != DF_REF_BB (use)->loop_father
+ && (!reg_single_def_p (SET_SRC (def_set))
+ || !reg_single_def_p (SET_DEST (def_set))))
+ return false;
+
/* Only try one kind of propagation. If two are possible, we'll
do it on the following iterations. */
if (forward_propagate_and_simplify (use, def_insn, def_set)
@@ -1483,7 +1553,7 @@ gate_fwprop (void)
}
static unsigned int
-fwprop (void)
+fwprop (bool fwprop_addr_p)
{
unsigned i;
@@ -1502,11 +1572,16 @@ fwprop (void)
df_ref use = DF_USES_GET (i);
if (use)
- if (DF_REF_TYPE (use) == DF_REF_REG_USE
- || DF_REF_BB (use)->loop_father == NULL
- /* The outer most loop is not really a loop. */
- || loop_outer (DF_REF_BB (use)->loop_father) == NULL)
- forward_propagate_into (use);
+ {
+ if (DF_REF_TYPE (use) == DF_REF_REG_USE
+ || DF_REF_BB (use)->loop_father == NULL
+ /* The outer most loop is not really a loop. */
+ || loop_outer (DF_REF_BB (use)->loop_father) == NULL)
+ forward_propagate_into (use, fwprop_addr_p);
+
+ else if (fwprop_addr_p)
+ forward_propagate_into (use, false);
+ }
}
fwprop_done ();
@@ -1537,7 +1612,7 @@ public:
/* opt_pass methods: */
virtual bool gate (function *) { return gate_fwprop (); }
- virtual unsigned int execute (function *) { return fwprop (); }
+ virtual unsigned int execute (function *) { return fwprop (false); }
}; // class pass_rtl_fwprop
@@ -1549,33 +1624,6 @@ make_pass_rtl_fwprop (gcc::context *ctxt)
return new pass_rtl_fwprop (ctxt);
}
-static unsigned int
-fwprop_addr (void)
-{
- unsigned i;
-
- fwprop_init ();
-
- /* Go through all the uses. df_uses_create will create new ones at the
- end, and we'll go through them as well. */
- for (i = 0; i < DF_USES_TABLE_SIZE (); i++)
- {
- if (!propagations_left)
- break;
-
- df_ref use = DF_USES_GET (i);
- if (use)
- if (DF_REF_TYPE (use) != DF_REF_REG_USE
- && DF_REF_BB (use)->loop_father != NULL
- /* The outer most loop is not really a loop. */
- && loop_outer (DF_REF_BB (use)->loop_father) != NULL)
- forward_propagate_into (use);
- }
-
- fwprop_done ();
- return 0;
-}
-
namespace {
const pass_data pass_data_rtl_fwprop_addr =
@@ -1600,7 +1648,7 @@ public:
/* opt_pass methods: */
virtual bool gate (function *) { return gate_fwprop (); }
- virtual unsigned int execute (function *) { return fwprop_addr (); }
+ virtual unsigned int execute (function *) { return fwprop (true); }
}; // class pass_rtl_fwprop_addr
diff --git a/gcc/testsuite/gfortran.dg/pr88833.f90 b/gcc/testsuite/gfortran.dg/pr88833.f90
new file mode 100644
index 00000000000..224e6ce5f3d
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr88833.f90
@@ -0,0 +1,9 @@
+! { dg-do assemble { target aarch64_asm_sve_ok } }
+! { dg-options "-O3 -march=armv8.2-a+sve --save-temps" }
+
+subroutine foo(x)
+ real :: x(100)
+ x = x + 10
+end subroutine foo
+
+! { dg-final { scan-assembler {\twhilelo\tp[0-9]+\.s, wzr, (w[0-9]+).*\twhilelo\tp[0-9]+\.s, w[0-9]+, \1} } }
