On Fri, Jun 5, 2026 at 4:19 AM Kyrylo Tkachov <[email protected]> wrote:
>
>
>
> > On 5 Jun 2026, at 12:11, Andrew Pinski <[email protected]>
> > wrote:
> >
> > This takes https://gcc.gnu.org/pipermail/gcc-patches/2026-June/719384.html
> > and merge it into factor_out_conditional_operation. Also expands it to
> > allow for more than just unary and binary operands.
> > It handles as similar as what ifcvt does in factor_out_operators
> > but rejects some cases due to those not being profitable.
> > The cases which are not profitable:
> > * pointer plus in early with constant operand 1 (except if equal).
> > * division/mod with constant operand 1
> >
> > some cases needed to be rejected for validity (copied from ifcvt):
> > * BIT_FIELD_REF/BIT_INSERT_EXPR (non first operand)
> > * VEC_PERM_EXPR with constant operand 2
> >
> > Notes on the testcase changes:
> > The recip-*.c testcases need to be disable phiopt since it removes
> > a division in some cases which causes the recip pass not to run.
> >
> > slsr-12.c and slsr-34.c need to be xfailed. SLSR pass is mostly
> > in maintaince mode and is not getting improved.
> >
> > pr122629-1.c and vect-reduc-cond-2.c are now handled in phiopt
> > rather than ifcvt.
> >
> > PR tree-optimization/125557
> > PR tree-optimization/64700
> > PR tree-optimization/29144
> > PR tree-optimization/94274
> > gcc/ChangeLog:
> >
> > * tree-if-conv.cc: Include tree-ssa-phiopt.h
> > (find_different_opnum): Move to ...
> > * tree-ssa-phiopt.cc (find_different_opnum): Here.
> > (is_divide_or_mod_p): New function.
> > (factor_out_conditional_operation): Handle operands > 1,
> > including operands communitive operands. Add early_p argument
> > for costing.
> > (pass_phiopt::execute): Pass early_p to
> > factor_out_conditional_operation.
> > * tree-ssa-phiopt.h: New file.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/tree-ssa/recip-3.c: Disable phiopt since it removes
> > one division and recip pass needs 3.
> > * gcc.dg/tree-ssa/recip-5.c: Likewise.
> > * gcc.dg/tree-ssa/recip-6.c: Likewise.
> > * gcc.dg/tree-ssa/recip-7.c: Likewise.
> > * gcc.dg/tree-ssa/slsr-12.c: xfail.
> > * gcc.dg/tree-ssa/slsr-34.c: Likewise.
> > * gcc.dg/tree-ssa/pr122629-1.c: Update to scan phiopt1.
> > * gcc.dg/vect/vect-reduc-cond-2.c: Likewise.
> > * gcc.dg/tree-ssa/phi-factor-binary-1.c: New test.
> > * gcc.dg/tree-ssa/phi-factor-binary-2.c: New test.
> > * gcc.target/aarch64/phi-factor-binary-1.c: New test.
> > Co-authored-by: Kyrylo Tkachov <[email protected]>
> >
> > Signed-off-by: Andrew Pinski <[email protected]>
> > ---
> > .../gcc.dg/tree-ssa/phi-factor-binary-1.c | 20 ++
> > .../gcc.dg/tree-ssa/phi-factor-binary-2.c | 41 +++++
> > gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c | 4 +-
> > gcc/testsuite/gcc.dg/tree-ssa/recip-3.c | 3 +
> > gcc/testsuite/gcc.dg/tree-ssa/recip-5.c | 2 +-
> > gcc/testsuite/gcc.dg/tree-ssa/recip-6.c | 2 +-
> > gcc/testsuite/gcc.dg/tree-ssa/recip-7.c | 2 +-
> > gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c | 2 +-
> > gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c | 2 +-
> > gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c | 4 +-
> > .../gcc.target/aarch64/phi-factor-binary-1.c | 60 ++++++
> > gcc/tree-if-conv.cc | 80 +-------
> > gcc/tree-ssa-phiopt.cc | 172 ++++++++++++++++--
> > gcc/tree-ssa-phiopt.h | 24 +++
> > 14 files changed, 319 insertions(+), 99 deletions(-)
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> > create mode 100644 gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> > create mode 100644 gcc/tree-ssa-phiopt.h
> >
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> > new file mode 100644
> > index 00000000000..bfcae888125
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> > @@ -0,0 +1,20 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -fdump-tree-phiopt1-details" } */
> > +
> > +/* PR tree-optimization/125557. Both arms of the diamond apply the same
> > binary
> > + operation sharing one operand (* c), so phi-opt factors it out: the join
> > + becomes t = PHI <a, b>; x = t * c -- one multiply at the merge instead
> > of
> > + one in each arm, and no extra PHI. */
> > +
> > +int
> > +f (int cond, int a, int b, int c)
> > +{
> > + int x;
> > + if (cond)
> > + x = a * c;
> > + else
> > + x = b * c;
> > + return x;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump " changed to factor operation out from
> > COND_EXP" "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> > new file mode 100644
> > index 00000000000..eb7669b664b
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> > @@ -0,0 +1,41 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -fdump-tree-phiopt1-details" } */
> > +
> > +/* tree-optimization/125557. factor_out_binary_common_operand handles
> > more than
> > + one operation kind and, when several join PHIs share the differing
> > operand,
> > + factors each of them -- collapsing the arms to a single select. */
> > +
> > +/* Two PHIs share the differing operand a/b: the multiply and the add are
> > each
> > + factored out, so both arms reduce to one select of a/b. */
> > +void
> > +f2 (int cond, int a, int b, int c, int d, int *p, int *q)
> > +{
> > + int x, y;
> > + if (cond)
> > + {
> > + x = a * c;
> > + y = a + d;
> > + }
> > + else
> > + {
> > + x = b * c;
> > + y = b + d;
> > + }
> > + *p = x;
> > + *q = y;
> > +}
> > +
> > +/* A shift is factored just like the arithmetic ops. */
> > +unsigned long
> > +f3 (int cond, unsigned long a, unsigned long b, int s)
> > +{
> > + unsigned long x;
> > + if (cond)
> > + x = a << s;
> > + else
> > + x = b << s;
> > + return x;
> > +}
> > +
> > +/* f2 factors twice (the * and the +), f3 once (the <<). */
> > +/* { dg-final { scan-tree-dump-times " changed to factor operation out
> > from COND_EXP" 3 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> > index a80d4a1990b..54f7bf11d48 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> > @@ -1,5 +1,5 @@
> > /* { dg-do compile } */
> > -/* { dg-options "-O2 -fdump-tree-ifcvt-details" } */
> > +/* { dg-options "-O2 -fdump-tree-ifcvt-details -fdump-tree-phiopt-details"
> > } */
> > /* PR tree-optimization/122629 */
> >
> > typedef int ix4 __attribute__((vector_size(4*sizeof(int))));
> > @@ -33,4 +33,4 @@ int g(ix4 *a, int l, int *b, ix4 *c)
> > }
> >
> > /* Make sure BIT_INSERT_EXPR/BIT_FIELD_REF is still factored out for the
> > case if operand 0 is different. */
> > -/* { dg-final { scan-tree-dump-times "changed to factor operation out
> > from" 2 "ifcvt" } } */
> > +/* { dg-final { scan-tree-dump-times "changed to factor operation out
> > from" 2 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> > index 036f32a9c33..3c6df8d0726 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> > @@ -5,6 +5,9 @@
> > to optimize a sequence. With a FP enabled ranger, we eliminate one of
> > them
> > earlier, causing the pass to skip this optimization. */
> > /* { dg-additional-options "-fno-thread-jumps -fno-tree-dominator-opts" } */
> > +/* PHI-OPT will factor out the `/d` from the `?:` expression which means
> > there will
> > + only be 2 `/d` left so disable that. */
> > +/* { dg-additional-options "-fno-ssa-phiopt" } */
> >
> > double F[5] = { 0.0, 0.0 }, e;
> >
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> > index 6ac0559bc7c..f05cfe866cc 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> > @@ -1,4 +1,4 @@
> > -/* { dg-options "-O1 -funsafe-math-optimizations -ftrapping-math
> > -fdump-tree-recip -fdump-tree-optimized" } */
> > +/* { dg-options "-O1 -funsafe-math-optimizations -ftrapping-math
> > -fdump-tree-recip -fdump-tree-optimized -fno-ssa-phiopt" } */
> > /* { dg-do compile } */
> > /* { dg-warning "'-fassociative-math' disabled" "" { target *-*-* } 0 } */
> >
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> > index b5d537a6ccd..c172fb34fcf 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> > @@ -1,4 +1,4 @@
> > -/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> > -fdump-tree-recip" } */
> > +/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> > -fdump-tree-recip -fno-ssa-phiopt" } */
> > /* { dg-do compile } */
> >
> > /* Test inserting in a block that does not contain a division. */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> > index 13fca0b0e09..0e205d17891 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> > @@ -1,4 +1,4 @@
> > -/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> > -fdump-tree-recip" } */
> > +/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> > -fdump-tree-recip -fno-ssa-phiopt" } */
> > /* { dg-do compile } */
> >
> > /* Test inserting in a block that does not contain a division. */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> > index f92b70ffafb..f50c2020157 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> > @@ -26,4 +26,4 @@ f (int s, int c)
> > return x;
> > }
> >
> > -/* { dg-final { scan-tree-dump-times " \\* " 3 "optimized" } } */
> > +/* { dg-final { scan-tree-dump-times " \\* " 3 "optimized" { xfail *-*-* }
> > } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> > index d7ede2efe8c..31d59b84d49 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> > @@ -38,5 +38,5 @@ f (int c, int i)
> > return x;
> > }
> >
> > -/* { dg-final { scan-tree-dump-times " \\* " 1 "optimized" } } */
> > +/* { dg-final { scan-tree-dump-times " \\* " 1 "optimized" { xfail *-*-* }
> > } } */
> > /* { dg-final { scan-tree-dump-times "PHI" 2 "optimized" } } */
> > diff --git a/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> > b/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> > index 126a50f3e56..aa204d1ab67 100644
> > --- a/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> > +++ b/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> > @@ -1,6 +1,6 @@
> > /* { dg-require-effective-target vect_int } */
> > /* { dg-require-effective-target vect_condition } */
> > -/* { dg-additional-options "-fdump-tree-ifcvt-details" } */
> > +/* { dg-additional-options "-fdump-tree-phiopt1-details" } */
> >
> > #include <stdarg.h>
> > #include "tree-vect.h"
> > @@ -59,4 +59,4 @@ int main (void)
> > }
> >
> > /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" { xfail
> > { vect_no_int_add } } } } */
> > -/* { dg-final { scan-tree-dump-times "changed to factor operation out from
> > COND_EXPR" 2 "ifcvt" } } */
> > +/* { dg-final { scan-tree-dump-times "changed to factor operation out from
> > COND_EXPR" 2 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> > b/gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> > new file mode 100644
> > index 00000000000..fd6b4f556c0
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> > @@ -0,0 +1,60 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2" } */
> > +
> > +/* tree-optimization/125557: factor_out_binary_common_operand computes a
> > binary
> > + operation shared between a PHI's two arms once, behind a single select,
> > + instead of once per arm -- and when several join PHIs share the
> > differing
> > + operand it collapses them to one select, which also removes the
> > + data-dependent branch. These are the asm wins of patch 1 on its own.
> > */
> > +
> > +/* f1: one multiply behind a select, not one per arm. */
> > +int
> > +f1 (int cond, int a, int b, int c)
> > +{
> > + int x;
> > + if (cond)
> > + x = a * c;
> > + else
> > + x = b * c;
> > + return x;
> > +}
> > +
> > +/* f3: one shift, not one per arm (snappy's address-arithmetic shape). */
> > +unsigned long
> > +f3 (int cond, unsigned long a, unsigned long b, int s)
> > +{
> > + unsigned long x;
> > + if (cond)
> > + x = a << s;
> > + else
> > + x = b << s;
> > + return x;
> > +}
> > +
> > +/* f2: two results share the differing operand (a/b): one select feeds
> > both, so
> > + only one multiply and one add remain and the diamond is branchless. */
> > +void
> > +f2 (int cond, int a, int b, int c, int d, int *p, int *q)
> > +{
> > + int x, y;
> > + if (cond)
> > + {
> > + x = a * c;
> > + y = a + d;
> > + }
> > + else
> > + {
> > + x = b * c;
> > + y = b + d;
> > + }
> > + *p = x;
> > + *q = y;
> > +}
> > +
> > +/* f1 and f2 each keep a single multiply (two without the factoring). */
> > +/* { dg-final { scan-assembler-times {\tmul\t} 2 } } */
> > +/* f3 keeps a single shift (two without the factoring). */
> > +/* { dg-final { scan-assembler-times {\tlsl\t} 1 } } */
> > +/* Each diamond becomes a branchless select; no data-dependent branch
> > remains. */
> > +/* { dg-final { scan-assembler-not {\tcbn?z\t} } } */
> > +/* { dg-final { scan-assembler-not {\tb\.[a-z]} } } */
> > diff --git a/gcc/tree-if-conv.cc b/gcc/tree-if-conv.cc
> > index b685e30bd0b..b8ae52100fb 100644
> > --- a/gcc/tree-if-conv.cc
> > +++ b/gcc/tree-if-conv.cc
> > @@ -124,6 +124,7 @@ along with GCC; see the file COPYING3. If not see
> > #include "tree-vectorizer.h"
> > #include "tree-eh.h"
> > #include "cgraph.h"
> > +#include "tree-ssa-phiopt.h"
> >
> > /* For lang_hooks.types.type_for_mode. */
> > #include "langhooks.h"
> > @@ -2173,85 +2174,6 @@ gen_phi_arg_condition (gphi *phi, ifcvt_arg_entry_t
> > &arg,
> > return cond;
> > }
> >
> > -/* Find the operand which is different between ARG0_OP and ARG1_OP.
> > - Returns the operand num where the difference is.
> > - Set NEWARG0 and NEWARG1 from the different argument.
> > - Returns -1 if none is found.
> > - If ARG0_OP/ARG1_OP is commutative also try swapping the
> > - two commutative operands and return the operand number where
> > - the difference happens in ARG0_OP. */
> > -
> > -static int
> > -find_different_opnum (const gimple_match_op &arg0_op,
> > - const gimple_match_op &arg1_op,
> > - tree *new_arg0, tree *new_arg1)
> > -{
> > - unsigned opnum = -1;
> > - unsigned first;
> > - first = first_commutative_argument (arg1_op.code, arg1_op.type);
> > - for (unsigned i = 0; i < arg0_op.num_ops; i++)
> > - {
> > - if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> > - arg1_op.ops[i]))
> > - {
> > - /* Can handle only one non equal operand. */
> > - if (opnum != -1u)
> > - {
> > - /* Though if opnum is right before i and opnum is equal
> > - to the first communtative argument, handle communtative
> > - specially. */
> > - if (i == opnum + 1 && opnum == first)
> > - goto commutative;
> > - return -1;
> > - }
> > - opnum = i;
> > - }
> > - }
> > - /* If all operands are equal only do this is there was single
> > - operand. */
> > - if (opnum == -1u)
> > - {
> > - if (arg0_op.num_ops != 1)
> > - return -1;
> > - opnum = 0;
> > - }
> > - *new_arg0 = arg0_op.ops[opnum];
> > - *new_arg1 = arg1_op.ops[opnum];
> > - return opnum;
> > -
> > -/* Handle commutative operations. */
> > -commutative:
> > - gcc_assert (first != -1u);
> > -
> > - /* Check the rest of the arguments to make sure they are the same. */
> > - for (unsigned i = first + 2; i < arg0_op.num_ops; i++)
> > - if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> > - arg1_op.ops[i]))
> > - return -1;
> > -
> > - /* If the arg0[first+1] and arg1[first] are the same
> > - then the one which is different is arg0[first] and arg1[first+1]
> > - return first since this is based on arg0. */
> > - if (operand_equal_for_phi_arg_p (arg0_op.ops[first + 1],
> > - arg1_op.ops[first]))
> > - {
> > - *new_arg0 = arg0_op.ops[first];
> > - *new_arg1 = arg1_op.ops[first + 1];
> > - return first;
> > - }
> > - /* If the arg0[first] and arg1[first+1] are the same
> > - then the one which is different is arg0[first+1] and arg1[first]
> > - return first+1 since this is based on arg0. */
> > - if (operand_equal_for_phi_arg_p (arg0_op.ops[first],
> > - arg1_op.ops[first + 1]))
> > - {
> > - *new_arg0 = arg0_op.ops[first + 1];
> > - *new_arg1 = arg1_op.ops[first];
> > - return first + 1;
> > - }
> > - return -1;
> > -}
> > -
> > /* Factors out an operation from *ARG0 and *ARG1 and
> > create the new statement at GSI. *RES is the
> > result of that new statement. Update *ARG0 and *ARG1
> > diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> > index 6a7e4c70722..f8881e61d2f 100644
> > --- a/gcc/tree-ssa-phiopt.cc
> > +++ b/gcc/tree-ssa-phiopt.cc
> > @@ -297,6 +297,104 @@ is_factor_profitable (gimple *def_stmt, basic_block
> > merge, tree arg)
> > return true;
> > }
> >
> > +/* Return true if CODE is an integer division or integer mod code. */
> > +static bool
> > +is_divide_or_mod_p (const code_helper &code)
> > +{
> > + switch (code.get_rep())
> > + {
> > + case TRUNC_DIV_EXPR:
> > + case CEIL_DIV_EXPR:
> > + case FLOOR_DIV_EXPR:
> > + case ROUND_DIV_EXPR:
> > + case EXACT_DIV_EXPR:
> > + case TRUNC_MOD_EXPR:
> > + case FLOOR_MOD_EXPR:
> > + return true;
> > + default:
> > + return false;
> > + }
> > +}
> > +
> > +/* Find the operand which is different between ARG0_OP and ARG1_OP.
> > + Returns the operand num where the difference is.
> > + Set NEWARG0 and NEWARG1 from the different argument.
> > + Returns -1 if none is found.
> > + If ARG0_OP/ARG1_OP is commutative also try swapping the
> > + two commutative operands and return the operand number where
> > + the difference happens in ARG0_OP. */
> > +
> > +int
> > +find_different_opnum (const gimple_match_op &arg0_op,
> > + const gimple_match_op &arg1_op,
> > + tree *new_arg0, tree *new_arg1)
> > +{
> > + unsigned opnum = -1;
> > + unsigned first;
> > + first = first_commutative_argument (arg1_op.code, arg1_op.type);
> > + for (unsigned i = 0; i < arg0_op.num_ops; i++)
> > + {
> > + if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> > + arg1_op.ops[i]))
> > + {
> > + /* Can handle only one non equal operand. */
> > + if (opnum != -1u)
> > + {
> > + /* Though if opnum is right before i and opnum is equal
> > + to the first communtative argument, handle communtative
> > + specially. */
> > + if (i == opnum + 1 && opnum == first)
> > + goto commutative;
> > + return -1;
> > + }
> > + opnum = i;
> > + }
> > + }
> > + /* If all operands are equal only do this is there was single
> > + operand. */
> > + if (opnum == -1u)
> > + {
> > + if (arg0_op.num_ops != 1)
> > + return -1;
> > + opnum = 0;
> > + }
> > + *new_arg0 = arg0_op.ops[opnum];
> > + *new_arg1 = arg1_op.ops[opnum];
> > + return opnum;
> > +
> > +/* Handle commutative operations. */
> > +commutative:
> > + gcc_assert (first != -1u);
> > +
> > + /* Check the rest of the arguments to make sure they are the same. */
> > + for (unsigned i = first + 2; i < arg0_op.num_ops; i++)
> > + if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> > + arg1_op.ops[i]))
> > + return -1;
> > +
> > + /* If the arg0[first+1] and arg1[first] are the same
> > + then the one which is different is arg0[first] and arg1[first+1]
> > + return first since this is based on arg0. */
> > + if (operand_equal_for_phi_arg_p (arg0_op.ops[first + 1],
> > + arg1_op.ops[first]))
> > + {
> > + *new_arg0 = arg0_op.ops[first];
> > + *new_arg1 = arg1_op.ops[first + 1];
> > + return first;
> > + }
> > + /* If the arg0[first] and arg1[first+1] are the same
> > + then the one which is different is arg0[first+1] and arg1[first]
> > + return first+1 since this is based on arg0. */
> > + if (operand_equal_for_phi_arg_p (arg0_op.ops[first],
> > + arg1_op.ops[first + 1]))
> > + {
> > + *new_arg0 = arg0_op.ops[first + 1];
> > + *new_arg1 = arg1_op.ops[first];
> > + return first + 1;
> > + }
> > + return -1;
> > +}
> > +
> > /* PR66726: Factor operations out of COND_EXPR. If the arguments of the PHI
> > stmt are Unary operator, factor out the operation and perform the
> > operation
> > to the result of PHI stmt. COND_STMT is the controlling predicate.
> > @@ -304,7 +402,8 @@ is_factor_profitable (gimple *def_stmt, basic_block
> > merge, tree arg)
> >
> > static bool
> > factor_out_conditional_operation (edge e0, edge e1, basic_block merge,
> > - gphi *phi, gimple *cond_stmt)
> > + gphi *phi, gimple *cond_stmt,
> > + bool early_p)
> > {
> > gimple *arg0_def_stmt = NULL, *arg1_def_stmt = NULL;
> > tree temp, result;
> > @@ -358,19 +457,14 @@ factor_out_conditional_operation (edge e0, edge e1,
> > basic_block merge,
> > if (arg0_op.operands_occurs_in_abnormal_phi ())
> > return false;
> >
> > - /* Currently just support one operand expressions. */
> > - if (arg0_op.num_ops != 1)
> > - return false;
> > -
> > - tree new_arg0 = arg0_op.ops[0];
> > + tree new_arg0;
> > tree new_arg1;
> > + int opnum = -1;
> >
> > /* If arg0 have > 1 use, then this transformation actually increases
> > the number of expressions evaluated at runtime. */
> > if (!has_single_use (arg0))
> > return false;
> > - if (!is_factor_profitable (arg0_def_stmt, merge, new_arg0))
> > - return false;
> > if (gimple_has_location (arg0_def_stmt))
> > narg0_loc = gimple_location (arg0_def_stmt);
> >
> > @@ -387,12 +481,62 @@ factor_out_conditional_operation (edge e0, edge e1,
> > basic_block merge,
> > if (arg1_op.operands_occurs_in_abnormal_phi ())
> > return false;
> >
> > + /* For the complex expression, don't factor
> > + out, that will confuse the uninitializing
> > + warnings. */
> > + if (arg1_op.code == COMPLEX_EXPR)
> > + return false;
>
> Btw, since you asked about it in your review of my patch, this is needed to
> avoid regressing gcc.dg/uninit-17.c
>
> > +
> > /* If arg1 have > 1 use, then this transformation actually increases
> > the number of expressions evaluated at runtime. */
> > if (!has_single_use (arg1))
> > return false;
> >
> > - new_arg1 = arg1_op.ops[0];
> > + opnum = find_different_opnum (arg0_op, arg1_op, &new_arg0,
> > &new_arg1);
> > + if (opnum == -1)
> > + return false;
> > + /* If this was a division and the operand is the divisor
> > + and either divisor was a constant, don't factor out
> > + the division; dividing by an explicit constant can be
> > + expanded better than without an constant.
> > + FIXME: maybe isel could undo this case. */
> > + if (is_divide_or_mod_p (arg1_op.code)
> > + && opnum == 1
> > + && (poly_int_tree_p (new_arg0)
> > + || poly_int_tree_p (new_arg1)))
> > + return false;
> > +
> > + /* For early phiopt, don't factor out constants for pointer plus
> > except if they are equal. */
> > + if (early_p && arg1_op.code == POINTER_PLUS_EXPR
> > + && opnum == 1
> > + && TREE_CODE (new_arg0) != SSA_NAME
> > + && TREE_CODE (new_arg1) != SSA_NAME
> > + && !operand_equal_p (new_arg0, new_arg1))
> > + return false;
>
> I think allowing the factoring of constants for other expressions like
> PLUS_EXPR leads to regressions in the aarch64 test suite in
> gcc.target/aarch64/cinc_common_1.c and gcc.target/aarch64/fuse_cmp_csel.c
fuse_cmp_csel.c looks like the scan should change.
It is better to put the add after the csel.
cinc_common_1.c seems like a missing combine due to splitting inefficiently:
```
Trying 26, 27 -> 13:
26: r105:SI=cc:CC<0
REG_DEAD cc:CC
27: r101:SI=r105:SI-0x2
REG_DEAD r105:SI
13: r104:SI=r101:SI+r103:SI
REG_DEAD r103:SI
REG_DEAD r101:SI
Failed to match this instruction:
(set (reg:SI 104 [ _3 ])
(plus:SI (plus:SI (lt:SI (reg:CC 66 cc)
(const_int 0 [0]))
(reg/v:SI 103 [ x ]))
(const_int -2 [0xfffffffffffffffe])))
Successfully matched this instruction:
(set (reg/v:SI 101 [ t ])
(lt:SI (reg:CC 66 cc)
(const_int 0 [0])))
Failed to match this instruction:
(set (reg:SI 104 [ _3 ])
(plus:SI (plus:SI (reg/v:SI 101 [ t ])
(reg/v:SI 103 [ x ]))
(const_int -2 [0xfffffffffffffffe])))
```
If we had split at:
(plus:SI (lt:SI (reg:CC 66 cc)
(const_int 0 [0]))
(reg/v:SI 103 [ x ]))
Instead then it would just work. Let me see if I can add an aarch64
pattern to fix this.
Note you can reproduce the same output by doing the transformation
this patch did manually in the code to show the issue.
I will file a bug for this and xfail the testcase too.
>
> I ran into the same thing and ended up replacing the narrow POINTER_PLUS
> guard with an unconditional "don't introduce a PHI of two constants” check.
>
> if (TREE_CODE (new_arg0) != SSA_NAME && TREE_CODE (new_arg1) != SSA_NAME)
> return false;
>
> This is a strict superset of the early_p POINTER_PLUS guard — the
> !operand_equal_p
> sub-case there can't actually be reached, since find_different_opnum only
> reports an operand as differing when it isn't operand-equal — so the
> POINTER_PLUS guard can be dropped. I think that would allow avoiding some
> slsr and recip tests fallout. But up to you if you want to keep it.
recip tests really are not testing the correct thing any more which is
why -fno-ssa-phiopt is needed. The number of divisions were never 3 in
it; it was just faked that way with the non-factored case.
I was thinking about lessening the restriction on find_different_opnum
and on the "same" operand and return 0. or return -2 for all the same
to factor it without a phi. But that is for a different patch on top
of this one.
So yes operand_equal should be dropped.
>
> Thanks,
> Kyrill
>
> > +
> > + /* BIT_FIELD_REF and BIT_INSERT_EXPR can't be factored out for non-0
> > operands
> > + as the other operands require constants. */
> > + if ((arg1_op.code == BIT_FIELD_REF
> > + || arg1_op.code == BIT_INSERT_EXPR)
> > + && opnum != 0)
> > + return false;
> > +
> > + /* It is not profitability to factor out vec_perm with
> > + constant masks (operand 2). The target might not support it
> > + and that might be invalid to do as such. Also with constants
> > + masks, the number of elements of the mask type does not need
> > + to match the number of elements of other operands and can be
> > + arbitrary integral vector type so factoring that out can't work.
> > + Note in the case where one mask is a constant and the other is not,
> > + the next check for compatible types will reject the case the
> > + constant mask has the incompatible type. */
> > + if (arg1_op.code == VEC_PERM_EXPR && opnum == 2
> > + && TREE_CODE (new_arg0) == VECTOR_CST
> > + && TREE_CODE (new_arg1) == VECTOR_CST)
> > + return false;
> > +
> > + if (!is_factor_profitable (arg0_def_stmt, merge, new_arg0))
> > + return false;
> > if (!is_factor_profitable (arg1_def_stmt, merge, new_arg1))
> > return false;
> > if (gimple_has_location (arg1_def_stmt))
> > @@ -409,14 +553,20 @@ factor_out_conditional_operation (edge e0, edge e1,
> > basic_block merge,
> > locus = narg0_loc;
> > }
> > }
> > + else if (arg0_op.num_ops != 1)
> > + return false;
> > else
> > {
> > + new_arg0 = arg0_op.ops[0];
> > + opnum = 0;
> > /* For constants only handle if the phi was the only one. */
> > if (single_non_singleton_phi_for_edges (phi_nodes (merge), e0, e1) ==
> > NULL)
> > return false;
> > /* TODO: handle more than just casts here. */
> > if (!gimple_assign_cast_p (arg0_def_stmt))
> > return false;
> > + if (!is_factor_profitable (arg0_def_stmt, merge, new_arg0))
> > + return false;
> >
> > /* arg0_def_stmt should be conditional. */
> > if (dominated_by_p (CDI_DOMINATORS, gimple_bb (phi), gimple_bb
> > (arg0_def_stmt)))
> > @@ -509,7 +659,7 @@ factor_out_conditional_operation (edge e0, edge e1,
> > basic_block merge,
> > gimple_match_op new_op = arg0_op;
> >
> > /* Create the operation stmt if possible and insert it. */
> > - new_op.ops[0] = temp;
> > + new_op.ops[opnum] = temp;
> > gimple_seq seq = NULL;
> > result = maybe_push_res_to_seq (&new_op, &seq, result);
> >
> > @@ -4105,7 +4255,7 @@ pass_phiopt::execute (function *)
> > gphi *phi = as_a <gphi *> (gsi_stmt (gsi));
> >
> > if (factor_out_conditional_operation (e1, e2, merge, phi,
> > - cond_stmt))
> > + cond_stmt, early_p))
> > {
> > /* Start over if there was an operation that was factored out because the
> > new phi might have another opportunity. */
> > phis = phi_nodes (merge);
> > diff --git a/gcc/tree-ssa-phiopt.h b/gcc/tree-ssa-phiopt.h
> > new file mode 100644
> > index 00000000000..bba3136965d
> > --- /dev/null
> > +++ b/gcc/tree-ssa-phiopt.h
> > @@ -0,0 +1,24 @@
> > +/* Copyright (C) 2026 Free Software Foundation, Inc.
> > +
> > +This file is part of GCC.
> > +
> > +GCC is free software; you can redistribute it and/or modify it
> > +under the terms of the GNU General Public License as published by the
> > +Free Software Foundation; either version 3, or (at your option) any
> > +later version.
> > +
> > +GCC is distributed in the hope that it will be useful, but WITHOUT
> > +ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> > +FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
> > +for more details.
> > +
> > +You should have received a copy of the GNU General Public License
> > +along with GCC; see the file COPYING3. If not see
> > +<http://www.gnu.org/licenses/>. */
> > +
> > +#ifndef TREE_SSA_PHIOPT_H
> > +#define TREE_SSA_PHIOPT_H
> > +extern int find_different_opnum (const gimple_match_op &arg0_op,
> > + const gimple_match_op &arg1_op,
> > + tree *new_arg0, tree *new_arg1);
> > +#endif
> > --
> > 2.43.0
> >
>
