> -----Original Message-----
> From: Andrea Pinski <[email protected]>
> Sent: 07 July 2026 16:43
> To: Tamar Christina <[email protected]>
> Cc: [email protected]; nd <[email protected]>; [email protected];
> Richard Earnshaw <[email protected]>; [email protected];
> Alex Coplan <[email protected]>; Wilco Dijkstra
> <[email protected]>; Alice Carlotti <[email protected]>;
> [email protected]; [email protected]
> Subject: Re: [patch]middle-end: Teach ranger about POLY_INT_CST ranges for
> VRP.
>
> On Tue, Jul 7, 2026 at 3:18 AM Tamar Christina <[email protected]>
> wrote:
> >
> > Hopefully this isn't controversial :)
> >
> > A an area where LLVM generates much better code than GCC today is in
> > optimization of VLA branches guarded by VLA constants.
> >
> > Normally in GIMPLE POLY_INT_CSTs have no upport and lower bound
> because well,
> > they're poly. However SVE has defined minimum and maximum vector sizes
> in
> > the architecture[1] and so for us we do have bounds on these constants.
> >
> > [1] https://developer.arm.com/documentation/102476/0101/Introducing-
> SVE
> >
> > Today LLVM optimizes these simple expressions
> >
> > #include <arm_sve.h>
> >
> > int g (void)
> > {
> > unsigned int vl = svcntb ();
> > return vl < 257;
> > }
> >
> > int h (void)
> > {
> > return svcntw () <= 64;
> > }
> >
> > away to
> >
> > g():
> > mov w0, #1
> > ret
> >
> > h():
> > mov w0, #1
> > ret
> >
> > which is right because both are always true for any SVE vector length.
> >
> > while GCC generates:
> >
> > g():
> > cntb x0
> > cmp w0, 257
> > cset w0, cc
> > ret
> > h():
> > cntw x0
> > cmp x0, 65
> > cset w0, cc
> > ret
> >
> > This patch extends ranger with a target hook poly_int_cst_value_range
> which
> > is different from the current costing only hooks used in the vectorizer
> because
> > those hooks can't be relied upon for correctness.
> >
> > This new hook allows us specify the minimum and maximum bounds of a
> POLY_INT_CST
> > and have ranger use it in range_query::get_tree_range.
> >
> > This gets GCC to fold away many known true or known false comparisons in
> > codegen today and we generate much simpler loop pre-headers.
> >
> > I have kept the AArch64 parts in this patch to get some extra eyes on it,
> > but
> > will split them out on commit.
> >
> > Bootstrapped Regtested on aarch64-none-linux-gnu,
> > arm-none-linux-gnueabihf, x86_64-pc-linux-gnu
> > -m32, -m64 and no issues.
> >
> > Ok for master?
>
> I think min is already detected correctly. It is just max that is needed here.
> So maybe the interface should just handle max.
> On the other hand, I noticed things like `POLY_INT_CST [16, 16] > 15`
> are not optimized right now either.
> This is because poly_int_binop does not handle GT_EXPR.
> The question becomes for the cases need to handle are formed together
> and poly_int_binop will be called?
> If so then maybe the interface should just be called from there
> instead of the VRP?
With the patch this fold correctly though. I do prefer this in VRP rather than
a specific folding interface since I'd imagine the range information to be
in general a useful thing to have which can be used for other optimizations.
Thanks,
Tamar
>
> Thanks,
> Andrea
>
> >
>
> >
> > Thanks,
> > Tamar
> >
> > gcc/ChangeLog:
> >
> > * config/aarch64/aarch64.cc (aarch64_poly_int_cst_value_range): New.
> > (TARGET_POLY_INT_CST_VALUE_RANGE): Implement hook using it.
> > * target.def (poly_int_cst_value_range): New.
> > * doc/tm.texi.in: Document it.
> > * doc/tm.texi: Regenerate.
> > * targhooks.cc (default_poly_int_cst_value_range): New.
> > * targhooks.h (default_poly_int_cst_value_range): New.
> > * value-query.cc (range_query::get_tree_range): Use it.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.target/aarch64/sve/slp_12.c: Update testcases
> > * gcc.target/aarch64/sve/cnt_fold_7.c: New test.
> > * gcc.target/aarch64/sve/cnt_fold_7_run.c: New test.
> >
> > ---
> > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> > index
> 72822ca621f52afee144bffa76bc75aac28adae1..7e12bb0e2c003b80008dd0
> f3c9fa304c7273ef39 100644
> > --- a/gcc/config/aarch64/aarch64.cc
> > +++ b/gcc/config/aarch64/aarch64.cc
> > @@ -31053,6 +31053,27 @@ aarch64_estimated_poly_value (poly_int64
> val,
> > return val.coeffs[0] + val.coeffs[1] * over_128 / 128;
> > }
> >
> > +/* Implement TARGET_POLY_INT_CST_VALUE_RANGE. */
> > +
> > +static bool
> > +aarch64_poly_int_cst_value_range (poly_int64 val, HOST_WIDE_INT
> *min_val,
> > + HOST_WIDE_INT *max_val)
> > +{
> > + unsigned int const_vg;
> > + if (aarch64_sve_vg.is_constant (&const_vg))
> > + {
> > + *min_val = val.coeffs[0];
> > + *max_val = *min_val;
> > + return true;
> > + }
> > +
> > + *min_val = val.coeffs[0];
> > + *max_val = val.coeffs[0] + val.coeffs[1] * 15;
> > + if (*min_val > *max_val)
> > + std::swap (*min_val, *max_val);
> > + return true;
> > +}
> > +
> >
> > /* Return true for types that could be supported as SIMD return or
> > argument types. */
> > @@ -34370,6 +34391,9 @@ aarch64_libgcc_floating_mode_supported_p
> > #undef TARGET_ESTIMATED_POLY_VALUE
> > #define TARGET_ESTIMATED_POLY_VALUE aarch64_estimated_poly_value
> >
> > +#undef TARGET_POLY_INT_CST_VALUE_RANGE
> > +#define TARGET_POLY_INT_CST_VALUE_RANGE
> aarch64_poly_int_cst_value_range
> > +
> > #undef TARGET_ATTRIBUTE_TABLE
> > #define TARGET_ATTRIBUTE_TABLE aarch64_attribute_table
> >
> > diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
> > index
> 6178db74d2fc5d14e8618ee655de05739cb3207c..bfb7e94cf163a75688e6f
> 99473bad4864a57fb24 100644
> > --- a/gcc/doc/tm.texi
> > +++ b/gcc/doc/tm.texi
> > @@ -7509,6 +7509,14 @@ the @code{POLY_VALUE_MIN},
> @code{POLY_VALUE_MAX} and
> > implementation returns the lowest possible value of @var{val}.
> > @end deftypefn
> >
> > +@deftypefn {Target Hook} bool TARGET_POLY_INT_CST_VALUE_RANGE
> (poly_int64 @var{val}, HOST_WIDE_INT *@var{min_val}, HOST_WIDE_INT
> *@var{max_val})
> > +Return true if the target can give a conservative inclusive range for
> > +the runtime value of @var{val}, storing the lower bound in @var{min_val}
> > +and the upper bound in @var{max_val}. This hook is used for correctness
> > +rather than for costing, so the returned bounds must be safe for all
> > +architecturally-valid runtime values.
> > +@end deftypefn
> > +
> > @deftypefn {Target Hook} bool TARGET_AVOID_STORE_FORWARDING_P
> (vec<store_fwd_info>, @var{rtx}, @var{int}, @var{bool})
> > Given a list of stores and a load instruction that reads from the location
> > of the stores, this hook decides if it's profitable to emit additional code
> > diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
> > index
> 0a97b0fa2e44014fa9e27d07a06d407a25e1ecc4..3aae8b2de9a3ecee41803
> a5dcba8f31b4af55b93 100644
> > --- a/gcc/doc/tm.texi.in
> > +++ b/gcc/doc/tm.texi.in
> > @@ -4812,6 +4812,8 @@ Define this macro if a non-short-circuit operation
> produced by
> >
> > @hook TARGET_ESTIMATED_POLY_VALUE
> >
> > +@hook TARGET_POLY_INT_CST_VALUE_RANGE
> > +
> > @hook TARGET_AVOID_STORE_FORWARDING_P
> >
> > @node Scheduling
> > diff --git a/gcc/target.def b/gcc/target.def
> > index
> 884fe1bd57e17b3ae92cd052a340f02a2559da31..aab20e89bb16fd9bb7d7
> 0d1c403268a65990a3e4 100644
> > --- a/gcc/target.def
> > +++ b/gcc/target.def
> > @@ -4217,6 +4217,16 @@ implementation returns the lowest possible
> value of @var{val}.",
> > HOST_WIDE_INT, (poly_int64 val, poly_value_estimate_kind kind),
> > default_estimated_poly_value)
> >
> > +DEFHOOK
> > +(poly_int_cst_value_range,
> > + "Return true if the target can give a conservative inclusive range for\n\
> > +the runtime value of @var{val}, storing the lower bound in
> @var{min_val}\n\
> > +and the upper bound in @var{max_val}. This hook is used for
> correctness\n\
> > +rather than for costing, so the returned bounds must be safe for all\n\
> > +architecturally-valid runtime values.",
> > + bool, (poly_int64 val, HOST_WIDE_INT *min_val, HOST_WIDE_INT
> *max_val),
> > + default_poly_int_cst_value_range)
> > +
> > /* Permit speculative instructions in delay slots during delayed-branch
> > scheduling. */
> > DEFHOOK
> > diff --git a/gcc/targhooks.cc b/gcc/targhooks.cc
> > index
> 388f696c8aa1050edbbc7efbdb01db60d84b4fe0..71f6f769e50298e32434e
> e94e87a1f3a3dfeef69 100644
> > --- a/gcc/targhooks.cc
> > +++ b/gcc/targhooks.cc
> > @@ -2164,6 +2164,19 @@ default_estimated_poly_value (poly_int64 x,
> poly_value_estimate_kind)
> > return x.coeffs[0];
> > }
> >
> > +/* The default implementation of TARGET_POLY_INT_CST_VALUE_RANGE.
> */
> > +
> > +bool
> > +default_poly_int_cst_value_range (poly_int64 x, HOST_WIDE_INT *min_val,
> > + HOST_WIDE_INT *max_val)
> > +{
> > + if (!x.is_constant (min_val))
> > + return false;
> > +
> > + *max_val = *min_val;
> > + return true;
> > +}
> > +
> > /* For hooks which use the MOVE_RATIO macro, this gives the legacy
> default
> > behavior. SPEED_P is true if we are compiling for speed. */
> >
> > diff --git a/gcc/targhooks.h b/gcc/targhooks.h
> > index
> 86de6ef8a699d72a36c665c697c89ca58314f3fe..90ebc1f514d47ca736c14a
> 641c69ab94f968bb1b 100644
> > --- a/gcc/targhooks.h
> > +++ b/gcc/targhooks.h
> > @@ -246,6 +246,8 @@ extern int default_frame_allocation_cost
> (frame_cost_type,
> > extern bool default_slow_unaligned_access (machine_mode, unsigned int);
> > extern HOST_WIDE_INT default_estimated_poly_value (poly_int64,
> >
> > poly_value_estimate_kind);
> > +extern bool default_poly_int_cst_value_range (poly_int64,
> HOST_WIDE_INT *,
> > + HOST_WIDE_INT *);
> >
> > extern bool default_use_by_pieces_infrastructure_p (unsigned
> HOST_WIDE_INT,
> > unsigned int,
> > diff --git a/gcc/testsuite/gcc.target/aarch64/sve/cnt_fold_7.c
> b/gcc/testsuite/gcc.target/aarch64/sve/cnt_fold_7.c
> > new file mode 100644
> > index
> 0000000000000000000000000000000000000000..d64933527da7e3e85f
> 37dc231355eb4cd30a1422
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/aarch64/sve/cnt_fold_7.c
> > @@ -0,0 +1,154 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2" } */
> > +/* { dg-final { check-function-bodies "**" "" } } */
> > +
> > +#include <arm_sve.h>
> > +
> > +/*
> > +** b_lt_257:
> > +** mov w0, 1
> > +** ret
> > +*/
> > +int
> > +b_lt_257 (void)
> > +{
> > + unsigned int vl = svcntb ();
> > +
> > + return vl < 257;
> > +}
> > +
> > +/*
> > +** h_ge_8:
> > +** mov w0, 1
> > +** ret
> > +*/
> > +int
> > +h_ge_8 (void)
> > +{
> > + return svcnth () >= 8;
> > +}
> > +
> > +/*
> > +** w_le_64:
> > +** mov w0, 1
> > +** ret
> > +*/
> > +int
> > +w_le_64 (void)
> > +{
> > + return svcntw () <= 64;
> > +}
> > +
> > +/*
> > +** d_gt_1:
> > +** mov w0, 1
> > +** ret
> > +*/
> > +int
> > +d_gt_1 (void)
> > +{
> > + return svcntd () > 1;
> > +}
> > +
> > +/*
> > +** b_ne_0:
> > +** mov w0, 1
> > +** ret
> > +*/
> > +int
> > +b_ne_0 (void)
> > +{
> > + return svcntb () != 0;
> > +}
> > +
> > +/*
> > +** b_le_15:
> > +** mov w0, 0
> > +** ret
> > +*/
> > +int
> > +b_le_15 (void)
> > +{
> > + return svcntb () <= 15;
> > +}
> > +
> > +/*
> > +** h_lt_8:
> > +** mov w0, 0
> > +** ret
> > +*/
> > +int
> > +h_lt_8 (void)
> > +{
> > + return svcnth () < 8;
> > +}
> > +
> > +/*
> > +** w_gt_64:
> > +** mov w0, 0
> > +** ret
> > +*/
> > +int
> > +w_gt_64 (void)
> > +{
> > + return svcntw () > 64;
> > +}
> > +
> > +/*
> > +** d_eq_0:
> > +** mov w0, 0
> > +** ret
> > +*/
> > +int
> > +d_eq_0 (void)
> > +{
> > + return svcntd () == 0;
> > +}
> > +
> > +/*
> > +** b_lt_256:
> > +** cntb x0
> > +** cmp x0, 256
> > +** cset w0, cc
> > +** ret
> > +*/
> > +int
> > +b_lt_256 (void)
> > +{
> > + return svcntb () < 256;
> > +}
> > +
> > +/*
> > +** w_gt_4:
> > +** cntw x0
> > +** cmp x0, 4
> > +** cset w0, hi
> > +** ret
> > +*/
> > +int
> > +w_gt_4 (void)
> > +{
> > + return svcntw () > 4;
> > +}
> > +
> > +/*
> > +** b_pat_all_lt_257:
> > +** mov w0, 1
> > +** ret
> > +*/
> > +int
> > +b_pat_all_lt_257 (void)
> > +{
> > + return svcntb_pat (SV_ALL) < 257;
> > +}
> > +
> > +/*
> > +** w_pat_all_le_64:
> > +** mov w0, 1
> > +** ret
> > +*/
> > +int
> > +w_pat_all_le_64 (void)
> > +{
> > + return svcntw_pat (SV_ALL) <= 64;
> > +}
> > diff --git a/gcc/testsuite/gcc.target/aarch64/sve/cnt_fold_7_run.c
> b/gcc/testsuite/gcc.target/aarch64/sve/cnt_fold_7_run.c
> > new file mode 100644
> > index
> 0000000000000000000000000000000000000000..59217ab343ec03509b
> ccc6d12098e6264adaa8b1
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/aarch64/sve/cnt_fold_7_run.c
> > @@ -0,0 +1,47 @@
> > +/* { dg-do run { target aarch64_sve_hw } } */
> > +/* { dg-options "-O2" } */
> > +
> > +#include <arm_sve.h>
> > +
> > +#define CHECK(EXPR) \
> > + do \
> > + { \
> > + if (!(EXPR)) \
> > + __builtin_abort (); \
> > + } \
> > + while (0)
> > +
> > +int
> > +main (void)
> > +{
> > + unsigned int b = svcntb ();
> > + unsigned int h = svcnth ();
> > + unsigned int w = svcntw ();
> > + unsigned int d = svcntd ();
> > +
> > + CHECK (b >= 16 && b <= 256);
> > + CHECK (h >= 8 && h <= 128);
> > + CHECK (w >= 4 && w <= 64);
> > + CHECK (d >= 2 && d <= 32);
> > +
> > + CHECK (b < 257);
> > + CHECK (h >= 8);
> > + CHECK (w <= 64);
> > + CHECK (d > 1);
> > + CHECK (b != 0);
> > +
> > + CHECK (!(b <= 15));
> > + CHECK (!(h < 8));
> > + CHECK (!(w > 64));
> > + CHECK (!(d == 0));
> > +
> > + CHECK ((svcntb () < 256) == (b < 256));
> > + CHECK ((svcntw () > 4) == (w > 4));
> > +
> > + CHECK (svcntb_pat (SV_ALL) == b);
> > + CHECK (svcntw_pat (SV_ALL) == w);
> > + CHECK (svcntb_pat (SV_ALL) < 257);
> > + CHECK (svcntw_pat (SV_ALL) <= 64);
> > +
> > + return 0;
> > +}
> > diff --git a/gcc/testsuite/gcc.target/aarch64/sve/slp_12.c
> b/gcc/testsuite/gcc.target/aarch64/sve/slp_12.c
> > index
> 0b9f8d9bdfaaf868ba0bd73ae83894c68e1613f8..0b1fef4d23a89b4fa46b45
> a2662924247eedce17 100644
> > --- a/gcc/testsuite/gcc.target/aarch64/sve/slp_12.c
> > +++ b/gcc/testsuite/gcc.target/aarch64/sve/slp_12.c
> > @@ -47,14 +47,12 @@ TEST_ALL (VEC_PERM)
> >
> > /* We should use WHILEs for all accesses. */
> > /* { dg-final { scan-assembler-times {\twhilelo\tp[0-7]\.b} 20 } } */
> > -/* { dg-final { scan-assembler-times {\twhilelo\tp[0-7]\.h} 20 } } */
> > -/* { dg-final { scan-assembler-times {\twhilelo\tp[0-7]\.s} 30 } } */
> > -/* { dg-final { scan-assembler-times {\twhilelo\tp[0-7]\.d} 30 } } */
> > +/* { dg-final { scan-assembler-times {\twhilelo\tp[0-7]\.h} 18 } } */
> > +/* { dg-final { scan-assembler-times {\twhilelo\tp[0-7]\.s} 24 } } */
> > +/* { dg-final { scan-assembler-times {\twhilelo\tp[0-7]\.d} 21 } } */
> >
> > /* 6 for the 8-bit types and 2 for the 16-bit types. */
> > /* { dg-final { scan-assembler-times {\tuqdecb\t} 8 } } */
> > -/* 4 for the 16-bit types and 3 for the 32-bit types. */
> > -/* { dg-final { scan-assembler-times {\tuqdech\t} 7 } } */
> > -/* 6 for the 32-bit types and 3 for the 64-bit types. */
> > -/* { dg-final { scan-assembler-times {\tuqdecw\t} 9 } } */
> > -/* { dg-final { scan-assembler-times {\tuqdecd\t} 6 } } */
> > +/* { dg-final { scan-assembler-times {\tuqdech\t} 2 } } */
> > +/* { dg-final { scan-assembler-times {\tuqdecw\t} 3 } } */
> > +/* { dg-final { scan-assembler-not {\tuqdecd\t} } } */
> > diff --git a/gcc/value-query.cc b/gcc/value-query.cc
> > index
> decf4e4d0ac0eddb2dd6657072bf7c62c2e2ed00..5ce7fac4caeddccd62b587
> d11b2174a1d0979bac 100644
> > --- a/gcc/value-query.cc
> > +++ b/gcc/value-query.cc
> > @@ -32,6 +32,7 @@ along with GCC; see the file COPYING3. If not see
> > #include "alloc-pool.h"
> > #include "gimple-range.h"
> > #include "value-range-storage.h"
> > +#include "target.h"
> >
> > // range_query default methods.
> >
> > @@ -404,7 +405,20 @@ range_query::get_tree_range (vrange &r, tree expr,
> gimple *stmt,
> > if (POLY_INT_CST_P (expr))
> > {
> > unsigned int precision = TYPE_PRECISION (type);
> > - r.set_varying (type);
> > + HOST_WIDE_INT min_val, max_val;
> > + if (tree_fits_poly_int64_p (expr)
> > + && targetm.poly_int_cst_value_range (tree_to_poly_int64
> > (expr),
> > + &min_val, &max_val))
> > + {
> > + wide_int min = wi::shwi (min_val, precision);
> > + wide_int max = wi::shwi (max_val, precision);
> > + if (wi::le_p (min, max, TYPE_SIGN (type)))
> > + as_a <irange> (r).set (type, min, max);
> > + else
> > + r.set_varying (type);
> > + }
> > + else
> > + r.set_varying (type);
> > r.update_bitmask ({ wi::zero (precision), get_nonzero_bits (expr)
> > });
> > return true;
> > }
> >
> >
> > --
