> gcc/ChangeLog:
>
> * Makefile.in: Add hierarchical_discriminator.o to OBJS.
> * hierarchical_discriminator.cc: New file.
> * hierarchical_discriminator.h: New file.
> * input.cc (location_with_discriminator_components): New function.
> (get_discriminator_components_from_loc): Likewise.
> * input.h (DISCR_BASE_BITS): New constant.
> (DISCR_MULTIPLICITY_BITS): Likewise.
> (DISCR_COPYID_BITS): Likewise.
> (DISCR_UNUSED_BITS): Likewise.
> (DISCR_BASE_MASK): Likewise.
> (DISCR_MULTIPLICITY_MASK): Likewise.
> (DISCR_COPYID_MASK): Likewise.
> (DISCR_BASE_SHIFT): Likewise.
> (DISCR_MULTIPLICITY_SHIFT): Likewise.
> (DISCR_COPYID_SHIFT): Likewise.
> (DISCR_BASE_MAX): Likewise.
> (DISCR_MULTIPLICITY_MAX): Likewise.
> (DISCR_COPYID_MAX): Likewise.
> (location_with_discriminator_components): New function declaration.
> (get_discriminator_components_from_loc): Likewise.
>
> Signed-off-by: Kugan Vivekanandarajah <[email protected]>
>
> Thanks,
> Kugan
>
>
> From 46968fce3960772ddbefb9e62bde7512fd8fb8b3 Mon Sep 17 00:00:00 2001
> From: Kugan Vivekanandarajah <[email protected]>
> Date: Tue, 11 Nov 2025 18:00:08 -0800
> Subject: [PATCH 1/4] [Autofdo] Add hierarchical discriminator support
>
> This patch introduces the basic infrastructure for hierarchical
> discriminators with format [Base:8][Multiplicity:7][CopyID:11][Unused:6].
> It adds helper functions to create and extract discriminator components.
>
> gcc/ChangeLog:
>
> * Makefile.in: Add hierarchical_discriminator.o to OBJS.
> * hierarchical_discriminator.cc: New file.
> * hierarchical_discriminator.h: New file.
> * input.cc (location_with_discriminator_components): New function.
> (get_discriminator_components_from_loc): Likewise.
> * input.h (DISCR_BASE_BITS): New constant.
> (DISCR_MULTIPLICITY_BITS): Likewise.
> (DISCR_COPYID_BITS): Likewise.
> (DISCR_UNUSED_BITS): Likewise.
> (DISCR_BASE_MASK): Likewise.
> (DISCR_MULTIPLICITY_MASK): Likewise.
> (DISCR_COPYID_MASK): Likewise.
> (DISCR_BASE_SHIFT): Likewise.
> (DISCR_MULTIPLICITY_SHIFT): Likewise.
> (DISCR_COPYID_SHIFT): Likewise.
> (DISCR_BASE_MAX): Likewise.
> (DISCR_MULTIPLICITY_MAX): Likewise.
> (DISCR_COPYID_MAX): Likewise.
> (location_with_discriminator_components): New function declaration.
> (get_discriminator_components_from_loc): Likewise.
>
> Signed-off-by: Kugan Vivekanandarajah <[email protected]>
> ---
> gcc/Makefile.in | 1 +
> gcc/hierarchical_discriminator.cc | 108 ++++++++++++++++++++++++++++++
> gcc/hierarchical_discriminator.h | 80 ++++++++++++++++++++++
> gcc/input.cc | 35 ++++++++++
> gcc/input.h | 40 +++++++++++
> 5 files changed, 264 insertions(+)
> create mode 100644 gcc/hierarchical_discriminator.cc
> create mode 100644 gcc/hierarchical_discriminator.h
>
> +/* Assign discriminators to all statements in a basic block. This
> + function updates the multiplicity and/or copyid discriminator components
> for
> + all statements in the given basic block, while preserving the base
> + discriminator. */
> +
> +void
> +assign_discriminators_to_bb (basic_block bb,
> + unsigned int multiplicity_value,
> + unsigned int copyid_value,
> + bool update_multiplicity,
> + bool update_copyid)
I would also add stmt version....
> +{
> + gimple_stmt_iterator gsi;
> +
> + for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> + {
> + gimple *stmt = gsi_stmt (gsi);
> + location_t loc = gimple_location (stmt);
> +
> + if (loc == UNKNOWN_LOCATION || is_gimple_debug (stmt))
> + continue;
> +
> + /* Get existing discriminator components. */
> + unsigned int base, multiplicity, copyid;
> + get_discriminator_components_from_loc (loc, &base,
> + &multiplicity, ©id);
> +
> + /* Update requested components. */
> + if (update_multiplicity)
> + multiplicity = multiplicity_value;
I wonder if it should not be multiplicity *=, since transformations can
combine.
> + if (update_copyid)
> + copyid = copyid_value;
> +
> + /* Set new location. */
> + location_t new_loc = location_with_discriminator_components (loc, base,
> + multiplicity,
> + copyid);
> + gimple_set_location (stmt, new_loc);
...
the reason is that there are some extra locators to update. PHI
statmenets, goto edges and also locations which can be placed in stmt
operands.
> +
> +/* Hierarchical discriminator layout (32 bits total):
> + Discriminator format: [Base:8][Multiplicity:7][CopyID:11][Unused:6]
> + - Base: bits 0-7 (8 bits, 0-255)
> + - Multiplicity: bits 8-14 (7 bits, 0-127)
> + - CopyID: bits 15-25 (11 bits, 0-2047)
> + - Unused: bits 26-31 (6 bits, reserved)
> +
> + Base discriminator: Used by front-end and early passes to distinguish
> + different statements on the same source line.
> +
> + Multiplicity: Duplication factor for unrolling/vectorization.
> + Represents how many times code is duplicated:
> + - Loop unrolling factor
> + - Vectorization width
> +
> + CopyID: Unique identifier for code copies to distinguish:
> + - Inlining contexts (different callsites)
> + - Function cloning
> +
> + Note: Loop unrolling and versioning use multiplicity, not copyid.
> + */
> +
> +/* Loop versioning discriminators (CopyID values). */
> +#define DISCRIMINATOR_LOOP_VERSION_VECTORIZED 1 /* Vectorized version. */
> +#define DISCRIMINATOR_LOOP_VERSION_SCALAR 2 /* Scalar version. */
> +#define DISCRIMINATOR_LOOP_VERSION_ALIGNED 3 /* Aligned version. */
> +#define DISCRIMINATOR_LOOP_VERSION_UNALIGNED 4 /* Unaligned version. */
> +#define DISCRIMINATOR_LOOP_PROLOG 6 /* Prolog loop. */
> +#define DISCRIMINATOR_LOOP_EPILOG 7 /* Epilog loop. */
> +#define DISCRIMINATOR_LOOP_EPILOG_VECTORIZED 8 /* Vector epilog loop. */
It is still not quite clear to me we want to go with pre-assigned copy
ID numbers. Optimizations can happen mulitple times at same loop (for
exmaple cascaded prologs). But I guess this is a good start, since it
is simple.
> +
> +/* Helper function to assign discriminators to all statements in a basic
> + block. This preserves the base discriminator and only updates the
> + requested components. */
> +extern void assign_discriminators_to_bb (basic_block bb,
> + unsigned int multiplicity_value,
> + unsigned int copyid_value,
> + bool update_multiplicity,
> + bool update_copyid);
> +
> +/* Helper function to assign discriminators to all basic blocks in a loop.
> + This is used by loop versioning passes to distinguish different versions
> + of the same loop and to indicate vectorization factors.
> +
> + multiplicity_value: vectorization factor (0 to keep unchanged)
> + copyid_value: version ID (1=vectorized, 2=scalar, etc.) */
> +extern void assign_discriminators_to_loop (class loop *loop,
> + unsigned int multiplicity_value,
> + unsigned int copyid_value);
> +
> +#endif /* GCC_HIERARCHICAL_DISCRIMINATOR_H. */
> diff --git a/gcc/input.cc b/gcc/input.cc
> index aad98394711..520ae33add8 100644
> --- a/gcc/input.cc
> +++ b/gcc/input.cc
> @@ -1074,6 +1074,41 @@ get_discriminator_from_loc (location_t locus)
> return get_discriminator_from_loc (line_table, locus);
> }
>
> +/* Create a location with hierarchical discriminator components. */
> +
> +location_t
> +location_with_discriminator_components (location_t locus,
> + unsigned int base,
> + unsigned int multiplicity,
> + unsigned int copyid)
Can you please put these values into a structure?
I think it will be then easier to add possible additional fields
and will be more handy to work with.
The patch looks good otherwise, but I think Jakub or Jason
(with more dwarf knowledge than me) probably should have chance to
comment. Since LLVM uses same scheme, I hope there is no problem with
having much bigger discriminators than before.
Honza
