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| -rw-r--r-- | gcc/ChangeLog | 4 | ||||
| -rw-r--r-- | gcc/config/h8300/h8300.c | 119 |
2 files changed, 23 insertions, 100 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 915591a..3d20349 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,7 @@ +2002-12-04 Kazu Hirata <kazu@cs.umass.edu> + + * config/h8300/h8300.c: Update the comments related to shifts. + 2002-12-04 Chris Demetriou <cgd@broadcom.com> * config/mips/mips.md (get_fnaddr): Correct length attribute. diff --git a/gcc/config/h8300/h8300.c b/gcc/config/h8300/h8300.c index 0d81b70..8451fec 100644 --- a/gcc/config/h8300/h8300.c +++ b/gcc/config/h8300/h8300.c @@ -2148,96 +2148,16 @@ compute_logical_op_cc (mode, operands) o SHIFT_LOOP: Emit a loop using one (or two on H8S) bit shifts. - Here are some thoughts on what the absolutely positively best code - is. "Best" here means some rational trade-off between code size - and speed, where speed is more preferred but not at the expense of - generating 20 insns. - - Below, a trailing '*' after the shift count indicates the "best" - mode isn't implemented. We only describe SHIFT_SPECIAL cases to - simplify the table. For other cases, refer to shift_alg_[qhs]i. - - H8/300 QImode shifts - 7 - ASHIFTRT: shll, subx (propagate carry bit to all bits) - - H8/300 HImode shifts - 7 - shift 2nd half other way into carry. - copy 1st half into 2nd half - rotate 2nd half other way with carry - rotate 1st half other way (no carry) - mask off bits in 1st half (ASHIFT | LSHIFTRT). - sign extend 1st half (ASHIFTRT) - 8 - move byte, zero (ASHIFT | LSHIFTRT) or sign extend other (ASHIFTRT) - 9-12 - do shift by 8, inline remaining shifts - 15 - ASHIFTRT: shll, subx, set other byte - - H8/300 SImode shifts - 7* - shift other way once, move bytes into place, - move carry into place (possibly with sign extension) - 8 - move bytes into place, zero or sign extend other - 15* - shift other way once, move word into place, move carry into place - 16 - move word, zero or sign extend other - 24* - move bytes into place, zero or sign extend other - 31 - ASHIFTRT: shll top byte, subx, copy to other bytes - - H8/300H QImode shifts (same as H8/300 QImode shifts) - 7 - ASHIFTRT: shll, subx (propagate carry bit to all bits) - - H8/300H HImode shifts - 7 - shift 2nd half other way into carry. - copy 1st half into 2nd half - rotate entire word other way using carry - mask off remaining bits (ASHIFT | LSHIFTRT) - sign extend remaining bits (ASHIFTRT) - 8 - move byte, zero (ASHIFT | LSHIFTRT) or sign extend other (ASHIFTRT) - 9-12 - do shift by 8, inline remaining shifts - 15 - ASHIFTRT: shll, subx, set other byte - - H8/300H SImode shifts - (These are complicated by the fact that we don't have byte level access to - the top word.) - A word is: bytes 3,2,1,0 (msb -> lsb), word 1,0 (msw -> lsw) - 15* - shift other way once, move word into place, move carry into place - (with sign extension for ASHIFTRT) - 16 - move word into place, zero or sign extend other - 17-20 - do 16bit shift, then inline remaining shifts - 24* - ASHIFT: move byte 0(msb) to byte 1, zero byte 0, - move word 0 to word 1, zero word 0 - LSHIFTRT: move word 1 to word 0, move byte 1 to byte 0, - zero word 1, zero byte 1 - ASHIFTRT: move word 1 to word 0, move byte 1 to byte 0, - sign extend byte 0, sign extend word 0 - 25-27* - either loop, or - do 24 bit shift, inline rest - 31 - shll, subx byte 0, sign extend byte 0, sign extend word 0 - - H8S QImode shifts - 7 - ASHIFTRT: shll, subx (propagate carry bit to all bits) - - H8S HImode shifts - 8 - move byte, zero (ASHIFT | LSHIFTRT) or sign extend other (ASHIFTRT) - 9-12 - do shift by 8, inline remaining shifts - 15 - ASHIFTRT: shll, subx, set other byte - - H8S SImode shifts - (These are complicated by the fact that we don't have byte level access to - the top word.) - A word is: bytes 3,2,1,0 (msb -> lsb), word 1,0 (msw -> lsw) - 15* - shift other way once, move word into place, move carry into place - (with sign extension for ASHIFTRT) - 16 - move word into place, zero or sign extend other - 17-20 - do 16bit shift, then inline remaining shifts - 24* - ASHIFT: move byte 0(msb) to byte 1, zero byte 0, - move word 0 to word 1, zero word 0 - LSHIFTRT: move word 1 to word 0, move byte 1 to byte 0, - zero word 1, zero byte 1 - ASHIFTRT: move word 1 to word 0, move byte 1 to byte 0, - sign extend byte 0, sign extend word 0 - 25-27* - either loop, or - do 24 bit shift, inline rest - 31 - shll, subx byte 0, sign extend byte 0, sign extend word 0 - - Panic!!! */ + For each shift count, we try to use code that has no trade-off + between code size and speed whenever possible. + + If the trade-off is unavoidable, we try to be reasonable. + Specifically, the fastest version is one instruction longer than + the shortest version, we take the fastest version. We also provide + the use a way to switch back to the shortest version with -Os. + + For the details of the shift algorithms for various shift counts, + refer to shift_alg_[qhs]i. */ int nshift_operator (x, mode) @@ -2474,16 +2394,15 @@ static void get_shift_alg PARAMS ((enum shift_type, /* Given SHIFT_TYPE, SHIFT_MODE, and shift count COUNT, determine the best algorithm for doing the shift. The assembler code is stored - in the pointers in INFO. We don't achieve maximum efficiency in - all cases, but the hooks are here to do so. - - For now we just use lots of switch statements. Since we don't even come - close to supporting all the cases, this is simplest. If this function ever - gets too big, perhaps resort to a more table based lookup. Of course, - at this point you may just wish to do it all in rtl. - - WARNING: The constraints on insns shiftbyn_QI/HI/SI assume shifts of - 1,2,3,4 will be inlined (1,2 for SI). */ + in the pointers in INFO. We achieve the maximum efficiency in most + cases when !TARGET_H8300. In case of TARGET_H8300, shifts in + SImode in particular have a lot of room to optimize. + + We first determine the strategy of the shift algorithm by a table + lookup. If that tells us to use a hand crafted assembly code, we + go into the big switch statement to find what that is. Otherwise, + we resort to a generic way, such as inlining. In either case, the + result is returned through INFO. */ static void get_shift_alg (shift_type, shift_mode, count, info) |