On 9/9/19 10:32 AM, Richard Sandiford wrote:
> This patch adds a bitmap_view<X> class that creates a read-only,
> on-stack bitmap representation of an array-like object X. The main
> use case is to allow HARD_REG_SETs to be used in REG_SET (i.e. bitmap)
> operations.
>
> For now it only handles constant-sized arrays, but I've tried to
> define the types in a way that could handle variable-sized arrays
> in future (although less efficiently). E.g. this might be useful
> for combining bitmaps and sbitmaps.
>
> For the read-only view to work as intended, I needed to make
> bitmap_bit_p take a const_bitmap instead of a bitmap. Logically
> the bitmap really is read-only, but we update the "current" and
> "indx" fields of the bitmap_head after doing a search.
>
> The patch makes this change using a const_cast. Another option
> was to make the fields mutable and push the constness down to
> bitmap_list_find_element and bitmap_tree_find_element.
> However, the constness of const_bitmap should apply to the bitmap
> as a whole rather than just the head structure, so if the input
> to those functions is a const_bitmap, the result should be a
> "const bitmap_element *". We'd therefore need overloaded versions of
> bitmap_*_find_element that take a constant bitmap and return a constant
> element (as for standard container accessors). These would be wrappers
> around the non-constant versions and themselves need a const_cast.
> All that seemed a bit over-the-top for an internal interface.
>
> I experimented with a few ways of writing the constructors, but the
> attached gave the best code. E.g. (for x86_64 users):
>
> void
> foo (bitmap a, const_hard_reg_set b)
> {
> bitmap_ior_into (a, bitmap_view<HARD_REG_SET> (b));
> }
>
> becomes:
>
> .cfi_startproc
> subq $88, %rsp
> .cfi_def_cfa_offset 96
> movq (%rsi), %rdx
> movq 8(%rsi), %rax
> movq $0, (%rsp)
> movq $0, 8(%rsp)
> movq %rdx, %rcx
> movq $0, 16(%rsp)
> orq %rax, %rcx
> movq $0, 24(%rsp)
> je .L645
> leaq 32(%rsp), %rcx
> movl $0, 48(%rsp)
> movq %rcx, 8(%rsp)
> movq $0, 40(%rsp)
> movq $0, 32(%rsp)
> movq %rcx, 16(%rsp)
> movq %rdx, 56(%rsp)
> movq %rax, 64(%rsp)
> .L645:
> movq %rsp, %rsi
> call _Z15bitmap_ior_intoP11bitmap_headPKS_
> addq $88, %rsp
> .cfi_def_cfa_offset 8
> ret
>
> which ought to be more efficient than the loops that the patch
> is replacing.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
>
> Richard
>
>
> 2019-09-09 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> * array-traits.h: New file.
> * coretypes.h (array_traits, bitmap_view): New types.
> * bitmap.h: Include "array-traits.h"
> (bitmap_bit_p): Take a const_bitmap instead of a bitmap.
> (base_bitmap_view, bitmap_view): New classes.
> * bitmap.c (bitmap_bit_p): Take a const_bitmap instead of a bitmap.
> * hard-reg-set.h: Include array-traits.h.
> (array_traits<HARD_REG_SET>): New struct.
> * regset.h (IOR_REG_SET_HRS): New macro.
> * loop-iv.c (simplify_using_initial_values): Use IOR_REG_SET_HRS
> rather than iterating over each hard register.
> * sched-deps.c (sched_analyze_insn): Likewise.
> * sel-sched-ir.c (setup_id_implicit_regs): Likewise.
OK
jeff
