Simplify the implementation of HARD_REG_SET

Programming / Compilers / GCC - rsandifo [138bc75d-0d04-0410-961f-82ee72b054a4] - 9 September 2019 17:58 EDT

We have two styles of HARD_REG_SET: a single integer based on HOST_WIDEST_FAST_INT (used when FIRST_PSEUDO_REGISTER is small enough) or an array of integers. One of the nice properties of this arrangement is that:

void foo (const HARD_REG_SET);

is passed by value as an integer when the set is small enough and by reference otherwise.

(This is in constrast to "const HARD_REG_SET &", which would always be passed by reference, and in contrast to passing a structure wrapper like "struct s { T elts[1]; }" by value, where the structure might be passed like a T or by reference, depending on the ABI.)

However, one of the disadvantages of using an array is that simple assignment doesn't work. We need to use COPY_HARD_REG_SET instead.

This patch uses a structure wrapper around the array, and preserves the above "nice property" using a new const_hard_reg_set typedef. The patch also removes the manual unrolling for small array sizes; I think these days we can rely on the compiler to do that for us.

This meant fixing two port-specific quirks:

- epiphany passed NULL as a HARD_REG_SET whose value doesn't matter. The patch passes the NO_REGS set instead.

- ia64 reused TEST_HARD_REG_BIT and SET_HARD_REG_BIT for arrays that are bigger than HARD_REG_SET. The patch just open-codes them.

The patch is probably being too conservative. Very few places actually take advantage of the "nice property" above, and we could have a cleaner interface if we used a structure wrapper for all cases.

2019-09-09 Richard Sandiford

- hard-reg-set.h (HARD_REG_SET): Define using a typedef rather than a #define. Use a structure rather than an array as the fallback definition. Remove special cases for low array sizes. (const_hard_reg_set): New typedef. (hard_reg_set_subset_p): Use it instead of "const HARD_REG_SET". (hard_reg_set_equal_p, hard_reg_set_intersect_p): Likewise. (hard_reg_set_empty_p): Likewise. (SET_HARD_REG_BIT): Use a function rather than a macro to handle the case in which HARD_REG_SET is a structure. (CLEAR_HARD_REG_BIT, TEST_HARD_REG_BIT, CLEAR_HARD_REG_SET) (SET_HARD_REG_SET, COPY_HARD_REG_SET, COMPL_HARD_REG_SET) (AND_HARD_REG_SET, AND_COMPL_HARD_REG_SET, IOR_HARD_REG_SET) (IOR_COMPL_HARD_REG_SET): Likewise. (hard_reg_set_iterator::pset): Constify the pointer target. (hard_reg_set_iter_init): Take a const_hard_reg_set instead of a "const HARD_REG_SET". Update the handling of non-integer HARD_REG_SETs.
- recog.h: Test HARD_CONST instead of CLEAR_HARD_REG_SET.
- reload.h: Likewise.
- rtl.h (choose_hard_reg_mode): Remove unnecessary line break.
- regs.h (in_hard_reg_set_p): Take a const_hard_reg_set instead of a "const HARD_REG_SET". (overlaps_hard_reg_set_p, range_overlaps_hard_reg_set_p): Likewise. (range_in_hard_reg_set_p): Likewise.
- ira-costs.c (restrict_cost_classes): Likewise.
- shrink-wrap.c (move_insn_for_shrink_wrap): Likewise.
- config/epiphany/resolve-sw-modes.c (pass_resolve_sw_modes::execute): Pass a NO_REGS HARD_REG_SET rather than NULL to emit_set_fp_mode.
- config/ia64/ia64.c (rws_insn): In the CHECKING_P version, use unsigned HOST_WIDEST_FAST_INT rather than HARD_REG_ELT_TYPE. (rws_insn_set, rws_insn_test): In the CHECKING_P version, take an unsigned int and open-code the HARD_REG_SET operations.

2ac0f18ef74 Simplify the implementation of HARD_REG_SET
gcc/ChangeLog | 35 +++
gcc/config/epiphany/resolve-sw-modes.c | 3 +-
gcc/config/ia64/ia64.c | 19 +-
gcc/hard-reg-set.h | 405 +++++++--------------------------
gcc/ira-costs.c | 2 +-
gcc/recog.h | 2 +-
gcc/regs.h | 8 +-
gcc/reload.h | 4 +-
gcc/rtl.h | 3 +-
gcc/shrink-wrap.c | 4 +-
10 files changed, 139 insertions(+), 346 deletions(-)


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