On Wed, 12 Nov 2025, Konstantinos Eleftheriou wrote: > This patch adds a new cost function so that the targets can decide if the > store/load reordering will be profitable. It also adds the > `asf-default-cost-value` parameter, which is used as the default return > value for the cost function.
It's a bit odd the param has "cost_value" and the hook says cost_p when this is a simple flag in the end. To that extent the "default" hook should be either returning true or false and the knob the user has is -f[no-]avoid-store-forwarding already, no need to add a --param. One could even say the target hook should _not_ have a default implementation and only targets that implement the hook should have the pass enabled - we only pay with compile-time cost otherwise. So please rework this part. Richard. > gcc/ChangeLog: > > * doc/tm.texi: Regenerate. > * doc/tm.texi.in: Document new target hook. > * params.opt: New parameter. > * target.def: New DEFHOOK. > * targhooks.cc (default_avoid_store_forwarding_reorder_cost_p): > New function. > * targhooks.h (default_avoid_store_forwarding_reorder_cost_p): > New function declaration. > > Signed-off-by: Konstantinos Eleftheriou <[email protected]> > --- > > (no changes since v1) > > gcc/doc/tm.texi | 7 +++++++ > gcc/doc/tm.texi.in | 2 ++ > gcc/params.opt | 4 ++++ > gcc/target.def | 9 +++++++++ > gcc/targhooks.cc | 9 +++++++++ > gcc/targhooks.h | 5 +++++ > 6 files changed, 36 insertions(+) > > diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi > index fd208f53844a..aef552aac5f8 100644 > --- a/gcc/doc/tm.texi > +++ b/gcc/doc/tm.texi > @@ -7466,6 +7466,13 @@ needed, the sequence cost and additional relevant > information is given in > the arguments so that the target can make an informed decision. > @end deftypefn > > +@deftypefn {Target Hook} bool TARGET_AVOID_STORE_FORWARDING_REORDER_COST_P > (machine_mode, @var{machine_mode}, @var{HOST_WIDE_INT}) > +This hook decides if it's profitable for the target to rearrange a store > +and a load instruction to avoid a potential store forwarding stall. > +The store and load modes and the byte offset of the store within the > +load are given as arguments. > +@end deftypefn > + > @node Scheduling > @section Adjusting the Instruction Scheduler > > diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in > index 14315dd50805..0c3168cb6dde 100644 > --- a/gcc/doc/tm.texi.in > +++ b/gcc/doc/tm.texi.in > @@ -4781,6 +4781,8 @@ Define this macro if a non-short-circuit operation > produced by > > @hook TARGET_AVOID_STORE_FORWARDING_P > > +@hook TARGET_AVOID_STORE_FORWARDING_REORDER_COST_P > + > @node Scheduling > @section Adjusting the Instruction Scheduler > > diff --git a/gcc/params.opt b/gcc/params.opt > index f8884e976e7f..96720651731d 100644 > --- a/gcc/params.opt > +++ b/gcc/params.opt > @@ -1091,6 +1091,10 @@ Maximum size of a single store merging region in bytes. > Common Joined UInteger Var(param_store_forwarding_max_distance) Init(10) > IntegerRange(0, 1000) Param Optimization > Maximum number of instruction distance that a small store forwarded to a > larger load may stall. Value '0' disables the cost checks for the > avoid-store-forwarding pass. > > +-param=asf-default-cost-value= > +Common Joined UInteger Var(param_asf_default_cost_value) Init(0) > IntegerRange(0, 1) Param Optimization > +Default return value for the avoid_store_forwarding_reorder_cost_p function. > + > -param=switch-conversion-max-branch-ratio= > Common Joined UInteger Var(param_switch_conversion_branch_ratio) Init(8) > IntegerRange(1, 65536) Param Optimization > The maximum ratio between array size and switch branches for a switch > conversion to take place. > diff --git a/gcc/target.def b/gcc/target.def > index f288329ffcab..d60510e5458e 100644 > --- a/gcc/target.def > +++ b/gcc/target.def > @@ -7158,6 +7158,15 @@ the arguments so that the target can make an informed > decision.", > bool, (vec<store_fwd_info>, rtx, int, bool), > default_avoid_store_forwarding_p) > > +DEFHOOK > +(avoid_store_forwarding_reorder_cost_p, > + "This hook decides if it's profitable for the target to rearrange a store\n\ > +and a load instruction to avoid a potential store forwarding stall.\n\ > +The store and load modes and the byte offset of the store within the\n\ > +load are given as arguments.", > + bool, (machine_mode, machine_mode, HOST_WIDE_INT), > + default_avoid_store_forwarding_reorder_cost_p) > + > /* Determine the type of unwind info to emit for debugging. */ > DEFHOOK > (debug_unwind_info, > diff --git a/gcc/targhooks.cc b/gcc/targhooks.cc > index 1873d572ba3f..15d882f4703e 100644 > --- a/gcc/targhooks.cc > +++ b/gcc/targhooks.cc > @@ -2352,6 +2352,15 @@ default_avoid_store_forwarding_p (vec<store_fwd_info>, > rtx, int total_cost, > return true; > } > > +/* The default implementation of TARGET_AVOID_STORE_FORWARDING_COST_P. */ > + > +bool > +default_avoid_store_forwarding_reorder_cost_p (machine_mode, machine_mode, > + HOST_WIDE_INT) > +{ > + return param_asf_default_cost_value; > +} > + > /* Determine the debugging unwind mechanism for the target. */ > > enum unwind_info_type > diff --git a/gcc/targhooks.h b/gcc/targhooks.h > index 92e7a4cb10f1..5389ea1cb78b 100644 > --- a/gcc/targhooks.h > +++ b/gcc/targhooks.h > @@ -264,6 +264,11 @@ extern unsigned char default_class_max_nregs > (reg_class_t, machine_mode); > extern bool default_avoid_store_forwarding_p (vec<store_fwd_info>, rtx, int, > bool); > > +extern bool > +default_avoid_store_forwarding_reorder_cost_p (machine_mode store_mode, > + machine_mode load_mode, > + HOST_WIDE_INT offset); > + > extern enum unwind_info_type default_debug_unwind_info (void); > > extern void default_canonicalize_comparison (int *, rtx *, rtx *, bool); > -- Richard Biener <[email protected]> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
