Submitter | Andrew Stubbs |
---|---|

Date | April 21, 2011, 11:23 a.m. |

Message ID | <4DB013B7.4090504@codesourcery.com> |

Download | mbox | patch |

Permalink | /patch/92396/ |

State | New |

Headers | show |

## Comments

On Thu, 2011-04-21 at 12:23 +0100, Andrew Stubbs wrote: > This patch is a repost of the one I previously posted here: > > http://gcc.gnu.org/ml/gcc-patches/2010-12/msg00652.html > > As requested, I've broken out the other parts of the original patch, and > those have already been reposted yesterday (and one committed also). > > This (final) part is support for using Thumb2's replicated constants and > addw/subw instructions as part of split constant loads. Previously the > compiler could use these constants, but only where they would be loaded > in a single instruction. > > This patch must be applied on top of the addw/subw patch I posted yesterday. > > The patch also optimizes the use of inverted or negated constants as a > short-cut to the final value. The previous code did this in some cases, > but could not be easily adapted to replicated constants. > > The previous code also had a bug that prevented optimal use of shifted > constants in Thumb code by imposing the same restrictions as ARM code. > This has been fixed. > > Example 1: addw as part of a split constant load > > a + 0xfffff > > Before: > movw r3, #65535 ; 0x0ffff > movt r3, 15 ; 0xf0000 > adds r3, r0, r3 > After: > add r0, r0, #1044480 ; 0xff000 > addw r0, r0, #4095 ; 0x00fff > > Example 2: arbitrary shifts bug fix > > a - 0xfff1 > > Before: > sub r0, r0, #65024 ; 0xfe00 > sub r0, r0, #496 ; 0x01f0 > sub r0, r0, #1 ; 0x0001 > After: > sub r0, r0, #65280 ; 0xff00 > sub r0, r0, #241 ; 0x00f1 > > Example 3: 16-bit replicated patterns > > a + 0x44004401 > > Before: > movw r3, #17409 ; 0x00004401 > movt r3, 17408 ; 0x44000000 > adds r3, r0, r3 > After: > add r0, r0, #1140868096 ; 0x44004400 > adds r0, r0, #1 ; 0x00000001 > > Example 4: 32-bit replicated patterns > > a & 0xaaaaaa00 > > Before: > mov r3, #43520 ; 0x0000aa00 > movt r3, 43690 ; 0xaaaa0000 > and r3, r0, r3 > After: > and r0, r0, #-1431655766 ; 0xaaaaaaaa > bic r0, r0, #170 ; 0x000000aa > > The constant splitting code was duplicated in two places, and I would > have needed to modify both quite heavily, so I have taken the > opportunity to unify the two, and hopefully reduce the future > maintenance burden. > > Let me respond to a point Richard Earnshaw raised following the original > posting: > > > A final note is that you may have missed some cases. Now that we have > > movw, > > reg& ~(16-bit const) > > can now be done in at most 2 insns: > > movw t1, #16-bit const > > bic Rd, reg, t1 > > Actually, I think we can do better than that for a 16-bit constant. > > Given: > > a & ~(0xabcd) > > Before my changes, GCC gave: > > bic r0, r0, #43520 > bic r0, r0, #460 > bic r0, r0, #1 > > and after applying my patch: > > bic r0, r0, #43776 > bic r0, r0, #205 > > Two instructions and no temporary register. > > > On thumb-2 you can also use ORN that way as well. > > It turns out that my previous patch was broken for ORN. I traced the > problem to some confusing code already in arm.c that set can_invert for > IOR, but then explicitly ignored it later (I had removed the second > part, but not the first). I posted, and committed a patch to fix this > yesterday. > > In fact ORN is only of limited use for this kind of thing. Like AND, you > can't use multiple ORNs to build a constant. The compiler already does > use ORN in some circumstances, and this patch has not changed that. > > Is the patch OK? > > Andrew + RETURN_SEQUENCE must be an int[4]. It would be a more robust coding style to define a struct with an int[4] array as its only member. Then it wouldn't be possible to pass an undersized object to these routines. OK with a change to do that. R.

## Patch

2011-04-21 Andrew Stubbs <ams@codesourcery.com> gcc/ * config/arm/arm.c: (count_insns_for_constant): Delete function. (find_best_start): Delete function. (optimal_immediate_sequence): New function. (optimal_immediate_sequence_1): New function. (arm_gen_constant): Move constant splitting code to optimal_immediate_sequence. Rewrite constant negation/invertion code. gcc/testsuite/ * gcc.target/arm/thumb2-replicated-constant1.c: New file. * gcc.target/arm/thumb2-replicated-constant2.c: New file. * gcc.target/arm/thumb2-replicated-constant3.c: New file. * gcc.target/arm/thumb2-replicated-constant4.c: New file. --- a/gcc/config/arm/arm.c +++ b/gcc/config/arm/arm.c @@ -129,7 +129,12 @@ static void thumb1_output_function_prologue (FILE *, HOST_WIDE_INT); static int arm_comp_type_attributes (const_tree, const_tree); static void arm_set_default_type_attributes (tree); static int arm_adjust_cost (rtx, rtx, rtx, int); -static int count_insns_for_constant (HOST_WIDE_INT, int); +static int optimal_immediate_sequence (enum rtx_code code, + unsigned HOST_WIDE_INT val, + int return_sequence[]); +static int optimal_immediate_sequence_1 (enum rtx_code code, + unsigned HOST_WIDE_INT val, + int return_sequence[], int i); static int arm_get_strip_length (int); static bool arm_function_ok_for_sibcall (tree, tree); static enum machine_mode arm_promote_function_mode (const_tree, @@ -2436,68 +2441,42 @@ arm_split_constant (enum rtx_code code, enum machine_mode mode, rtx insn, 1); } -/* Return the number of instructions required to synthesize the given - constant, if we start emitting them from bit-position I. */ +/* Return a sequence of integers, in RETURN_SEQUENCE that fit into + ARM/THUMB2 immediates, and add up to VAL. + RETURN_SEQUENCE must be an int[4]. + Thr function return value gives the number of insns required. */ static int -count_insns_for_constant (HOST_WIDE_INT remainder, int i) -{ - HOST_WIDE_INT temp1; - int step_size = TARGET_ARM ? 2 : 1; - int num_insns = 0; - - gcc_assert (TARGET_ARM || i == 0); - - do - { - int end; - - if (i <= 0) - i += 32; - if (remainder & (((1 << step_size) - 1) << (i - step_size))) - { - end = i - 8; - if (end < 0) - end += 32; - temp1 = remainder & ((0x0ff << end) - | ((i < end) ? (0xff >> (32 - end)) : 0)); - remainder &= ~temp1; - num_insns++; - i -= 8 - step_size; - } - i -= step_size; - } while (remainder); - return num_insns; -} - -static int -find_best_start (unsigned HOST_WIDE_INT remainder) +optimal_immediate_sequence (enum rtx_code code, unsigned HOST_WIDE_INT val, + int return_sequence[]) { int best_consecutive_zeros = 0; int i; int best_start = 0; + int insns1, insns2; + int tmp_sequence[4]; /* If we aren't targetting ARM, the best place to start is always at - the bottom. */ - if (! TARGET_ARM) - return 0; - - for (i = 0; i < 32; i += 2) + the bottom, otherwise look more closely. */ + if (TARGET_ARM) { - int consecutive_zeros = 0; - - if (!(remainder & (3 << i))) + for (i = 0; i < 32; i += 2) { - while ((i < 32) && !(remainder & (3 << i))) - { - consecutive_zeros += 2; - i += 2; - } - if (consecutive_zeros > best_consecutive_zeros) + int consecutive_zeros = 0; + + if (!(val & (3 << i))) { - best_consecutive_zeros = consecutive_zeros; - best_start = i - consecutive_zeros; + while ((i < 32) && !(val & (3 << i))) + { + consecutive_zeros += 2; + i += 2; + } + if (consecutive_zeros > best_consecutive_zeros) + { + best_consecutive_zeros = consecutive_zeros; + best_start = i - consecutive_zeros; + } + i -= 2; } - i -= 2; } } @@ -2524,13 +2503,161 @@ find_best_start (unsigned HOST_WIDE_INT remainder) the constant starting from `best_start', and also starting from zero (i.e. with bit 31 first to be output). If `best_start' doesn't yield a shorter sequence, we may as well use zero. */ + insns1 = optimal_immediate_sequence_1 (code, val, return_sequence, best_start); if (best_start != 0 - && ((((unsigned HOST_WIDE_INT) 1) << best_start) < remainder) - && (count_insns_for_constant (remainder, 0) <= - count_insns_for_constant (remainder, best_start))) - best_start = 0; + && ((((unsigned HOST_WIDE_INT) 1) << best_start) < val)) + { + insns2 = optimal_immediate_sequence_1 (code, val, tmp_sequence, 0); + if (insns2 <= insns1) + { + memcpy (return_sequence, tmp_sequence, sizeof(tmp_sequence)); + insns1 = insns2; + } + } + + return insns1; +} + +/* As for optimal_immediate_sequence, but starting at bit-position I. */ +static int +optimal_immediate_sequence_1 (enum rtx_code code, unsigned HOST_WIDE_INT val, + int return_sequence[], int i) +{ + int remainder = val & 0xffffffff; + int insns = 0; + + /* Try and find a way of doing the job in either two or three + instructions. + + In ARM mode we can use 8-bit constants, rotated to any 2-bit aligned + location. We start at position I. This may be the MSB, or + optimial_immediate_sequence may have positioned it at the largest block + of zeros that are aligned on a 2-bit boundary. We then fill up the temps, + wrapping around to the top of the word when we drop off the bottom. + In the worst case this code should produce no more than four insns. + + In Thumb2 mode, we can use 32/16-bit replicated constants, and 8-bit + constants, shifted to any arbitrary location. We should always start + at the MSB. */ + do + { + int end; + int b1, b2, b3, b4; + unsigned HOST_WIDE_INT result; + int loc; + + gcc_assert (insns < 4); + + if (i <= 0) + i += 32; + + /* First, find the next normal 12/8-bit shifted/rotated immediate. */ + if (remainder & ((TARGET_ARM ? (3 << (i - 2)) : (1 << (i - 1))))) + { + loc = i; + if (i <= 12 && TARGET_THUMB2 && code == PLUS) + /* We can use addw/subw for the last 12 bits. */ + result = remainder; + else + { + /* Use an 8-bit shifted/rotated immediate. */ + end = i - 8; + if (end < 0) + end += 32; + result = remainder & ((0x0ff << end) + | ((i < end) ? (0xff >> (32 - end)) + : 0)); + i -= 8; + } + } + else + { + /* Arm allows rotates by a multiple of two. Thumb-2 allows + arbitrary shifts. */ + i -= TARGET_ARM ? 2 : 1; + continue; + } + + /* Next, see if we can do a better job with a thumb2 replicated + constant. + + We do it this way around to catch the cases like 0x01F001E0 where + two 8-bit immediates would work, but a replicated constant would + make it worse. + + TODO: 16-bit constants that don't clear all the bits, but still win. + TODO: Arithmetic splitting for set/add/sub, rather than bitwise. */ + if (TARGET_THUMB2) + { + b1 = (remainder & 0xff000000) >> 24; + b2 = (remainder & 0x00ff0000) >> 16; + b3 = (remainder & 0x0000ff00) >> 8; + b4 = remainder & 0xff; + + if (loc > 24) + { + /* The 8-bit immediate already found clears b1 (and maybe b2), + but must leave b3 and b4 alone. */ + + /* First try to find a 32-bit replicated constant that clears + almost everything. We can assume that we can't do it in one, + or else we wouldn't be here. */ + unsigned int tmp = b1 & b2 & b3 & b4; + unsigned int tmp2 = tmp + (tmp << 8) + (tmp << 16) + + (tmp << 24); + unsigned int matching_bytes = (tmp == b1) + (tmp == b2) + + (tmp == b3) + (tmp == b4); + if (tmp + && (matching_bytes >= 3 + || (matching_bytes == 2 + && const_ok_for_op (remainder & ~tmp2, code)))) + { + /* At least 3 of the bytes match, and the fourth has at + least as many bits set, or two of the bytes match + and it will only require one more insn to finish. */ + result = tmp2; + i = tmp != b1 ? 32 + : tmp != b2 ? 24 + : tmp != b3 ? 16 + : 8; + } + + /* Second, try to find a 16-bit replicated constant that can + leave three of the bytes clear. If b2 or b4 is already + zero, then we can. If the 8-bit from above would not + clear b2 anyway, then we still win. */ + else if (b1 == b3 && (!b2 || !b4 + || (remainder & 0x00ff0000 & ~result))) + { + result = remainder & 0xff00ff00; + i = 24; + } + } + else if (loc > 16) + { + /* The 8-bit immediate already found clears b2 (and maybe b3) + and we don't get here unless b1 is alredy clear, but it will + leave b4 unchanged. */ + + /* If we can clear b2 and b4 at once, then we win, since the + 8-bits couldn't possibly reach that far. */ + if (b2 == b4) + { + result = remainder & 0x00ff00ff; + i = 16; + } + } + } + + return_sequence[insns++] = result; + remainder &= ~result; + + if (code == SET || code == MINUS) + code = PLUS; + } + while (remainder); - return best_start; + return insns; } /* Emit an instruction with the indicated PATTERN. If COND is @@ -2547,7 +2674,6 @@ emit_constant_insn (rtx cond, rtx pattern) /* As above, but extra parameter GENERATE which, if clear, suppresses RTL generation. */ -/* ??? This needs more work for thumb2. */ static int arm_gen_constant (enum rtx_code code, enum machine_mode mode, rtx cond, @@ -2559,15 +2685,14 @@ arm_gen_constant (enum rtx_code code, enum machine_mode mode, rtx cond, int final_invert = 0; int can_negate_initial = 0; int i; - int num_bits_set = 0; int set_sign_bit_copies = 0; int clear_sign_bit_copies = 0; int clear_zero_bit_copies = 0; int set_zero_bit_copies = 0; - int insns = 0; + int insns = 0, neg_insns, inv_insns; unsigned HOST_WIDE_INT temp1, temp2; unsigned HOST_WIDE_INT remainder = val & 0xffffffff; - int step_size = TARGET_ARM ? 2 : 1; + int immediates[4], neg_immediates[4], inv_immediates[4]; /* Find out which operations are safe for a given CODE. Also do a quick check for degenerate cases; these can occur when DImode operations @@ -3079,120 +3204,100 @@ arm_gen_constant (enum rtx_code code, enum machine_mode mode, rtx cond, break; } - for (i = 0; i < 32; i++) - if (remainder & (1 << i)) - num_bits_set++; + /* Calculate what the instruction sequences would be if we generated it + normally, negated, or inverted. */ + if (code == AND) + /* AND cannot be split into multiple insns, so invert and use BIC. */ + insns = 99; + else + insns = optimal_immediate_sequence (code, remainder, immediates); + + if (can_negate) + neg_insns = optimal_immediate_sequence (code, (-remainder) & 0xffffffff, + neg_immediates); + else + neg_insns = 99; - if ((code == AND) || (can_invert && num_bits_set > 16)) - remainder ^= 0xffffffff; - else if (code == PLUS && num_bits_set > 16) - remainder = (-remainder) & 0xffffffff; + if (can_invert) + inv_insns = optimal_immediate_sequence (code, remainder ^ 0xffffffff, + inv_immediates); + else + inv_insns = 99; - /* For XOR, if more than half the bits are set and there's a sequence - of more than 8 consecutive ones in the pattern then we can XOR by the - inverted constant and then invert the final result; this may save an - instruction and might also lead to the final mvn being merged with - some other operation. */ - else if (code == XOR && num_bits_set > 16 - && (count_insns_for_constant (remainder ^ 0xffffffff, - find_best_start - (remainder ^ 0xffffffff)) - < count_insns_for_constant (remainder, - find_best_start (remainder)))) + /* Is the negated immediate sequence more efficient? */ + if (neg_insns < insns && neg_insns <= inv_insns) { - remainder ^= 0xffffffff; - final_invert = 1; + insns = neg_insns; + memcpy (immediates, neg_immediates, sizeof (immediates)); } else + can_negate = 0; + + /* Is the inverted immediate sequence more efficient? + We must allow for an extra NOT instruction for XOR operations, although + there is some chance that the final 'mvn' will get optimized later. */ + if (inv_insns < insns && (code != XOR || (inv_insns + 1) < insns)) { - can_invert = 0; - can_negate = 0; - } + insns = inv_insns; + memcpy (immediates, inv_immediates, sizeof (immediates)); - /* Now try and find a way of doing the job in either two or three - instructions. - We start by looking for the largest block of zeros that are aligned on - a 2-bit boundary, we then fill up the temps, wrapping around to the - top of the word when we drop off the bottom. - In the worst case this code should produce no more than four insns. - Thumb-2 constants are shifted, not rotated, so the MSB is always the - best place to start. */ + if (code == XOR) + final_invert = 1; + } + else + can_invert = 0; - /* ??? Use thumb2 replicated constants when the high and low halfwords are - the same. */ - { - /* Now start emitting the insns. */ - i = find_best_start (remainder); - do - { - int end; + /* Now output the chosen sequence as instructions. */ + if (generate) + { + for (i = 0; i < insns; i++) + { + rtx new_src, temp1_rtx; - if (i <= 0) - i += 32; - if (remainder & (3 << (i - 2))) - { - end = i - 8; - if (end < 0) - end += 32; - temp1 = remainder & ((0x0ff << end) - | ((i < end) ? (0xff >> (32 - end)) : 0)); - remainder &= ~temp1; - - if (generate) - { - rtx new_src, temp1_rtx; + temp1 = immediates[i]; - if (code == SET || code == MINUS) - { - new_src = (subtargets ? gen_reg_rtx (mode) : target); - if (can_invert && code != MINUS) - temp1 = ~temp1; - } - else - { - if ((final_invert || remainder) && subtargets) - new_src = gen_reg_rtx (mode); - else - new_src = target; - if (can_invert) - temp1 = ~temp1; - else if (can_negate) - temp1 = -temp1; - } + if (code == SET || code == MINUS) + { + new_src = (subtargets ? gen_reg_rtx (mode) : target); + if (can_invert && code != MINUS) + temp1 = ~temp1; + } + else + { + if ((final_invert || i < (insns - 1)) && subtargets) + new_src = gen_reg_rtx (mode); + else + new_src = target; + if (can_invert) + temp1 = ~temp1; + else if (can_negate) + temp1 = -temp1; + } - temp1 = trunc_int_for_mode (temp1, mode); - temp1_rtx = GEN_INT (temp1); + temp1 = trunc_int_for_mode (temp1, mode); + temp1_rtx = GEN_INT (temp1); - if (code == SET) - ; - else if (code == MINUS) - temp1_rtx = gen_rtx_MINUS (mode, temp1_rtx, source); - else - temp1_rtx = gen_rtx_fmt_ee (code, mode, source, temp1_rtx); + if (code == SET) + ; + else if (code == MINUS) + temp1_rtx = gen_rtx_MINUS (mode, temp1_rtx, source); + else + temp1_rtx = gen_rtx_fmt_ee (code, mode, source, temp1_rtx); - emit_constant_insn (cond, - gen_rtx_SET (VOIDmode, new_src, - temp1_rtx)); - source = new_src; - } + emit_constant_insn (cond, + gen_rtx_SET (VOIDmode, new_src, + temp1_rtx)); + source = new_src; - if (code == SET) - { - can_invert = 0; - code = PLUS; - } - else if (code == MINUS) + if (code == SET) + { + can_invert = 0; code = PLUS; - - insns++; - i -= 8 - step_size; - } - /* Arm allows rotates by a multiple of two. Thumb-2 allows arbitrary - shifts. */ - i -= step_size; - } - while (remainder); - } + } + else if (code == MINUS) + code = PLUS; + } + } if (final_invert) { --- /dev/null +++ b/gcc/testsuite/gcc.target/arm/thumb2-replicated-constant1.c @@ -0,0 +1,27 @@ +/* Ensure simple replicated constant immediates work. */ +/* { dg-options "-mthumb -O2" } */ +/* { dg-require-effective-target arm_thumb2_ok } */ + +int +foo1 (int a) +{ + return a + 0xfefefefe; +} + +/* { dg-final { scan-assembler "add.*#-16843010" } } */ + +int +foo2 (int a) +{ + return a - 0xab00ab00; +} + +/* { dg-final { scan-assembler "sub.*#-1426019584" } } */ + +int +foo3 (int a) +{ + return a & 0x00cd00cd; +} + +/* { dg-final { scan-assembler "and.*#13435085" } } */ --- /dev/null +++ b/gcc/testsuite/gcc.target/arm/thumb2-replicated-constant2.c @@ -0,0 +1,75 @@ +/* Ensure split constants can use replicated patterns. */ +/* { dg-options "-mthumb -O2" } */ +/* { dg-require-effective-target arm_thumb2_ok } */ + +int +foo1 (int a) +{ + return a + 0xfe00fe01; +} + +/* { dg-final { scan-assembler "add.*#-33489408" } } */ +/* { dg-final { scan-assembler "add.*#1" } } */ + +int +foo2 (int a) +{ + return a + 0xdd01dd00; +} + +/* { dg-final { scan-assembler "add.*#-587145984" } } */ +/* { dg-final { scan-assembler "add.*#65536" } } */ + +int +foo3 (int a) +{ + return a + 0x00443344; +} + +/* { dg-final { scan-assembler "add.*#4456516" } } */ +/* { dg-final { scan-assembler "add.*#13056" } } */ + +int +foo4 (int a) +{ + return a + 0x77330033; +} + +/* { dg-final { scan-assembler "add.*#1996488704" } } */ +/* { dg-final { scan-assembler "add.*#3342387" } } */ + +int +foo5 (int a) +{ + return a + 0x11221122; +} + +/* { dg-final { scan-assembler "add.*#285217024" } } */ +/* { dg-final { scan-assembler "add.*#2228258" } } */ + +int +foo6 (int a) +{ + return a + 0x66666677; +} + +/* { dg-final { scan-assembler "add.*#1717986918" } } */ +/* { dg-final { scan-assembler "add.*#17" } } */ + +int +foo7 (int a) +{ + return a + 0x99888888; +} + +/* { dg-final { scan-assembler "add.*#-2004318072" } } */ +/* { dg-final { scan-assembler "add.*#285212672" } } */ + +int +foo8 (int a) +{ + return a + 0xdddddfff; +} + +/* { dg-final { scan-assembler "add.*#-572662307" } } */ +/* { dg-final { scan-assembler "addw.*#546" } } */ --- /dev/null +++ b/gcc/testsuite/gcc.target/arm/thumb2-replicated-constant3.c @@ -0,0 +1,28 @@ +/* Ensure negated/inverted replicated constant immediates work. */ +/* { dg-options "-mthumb -O2" } */ +/* { dg-require-effective-target arm_thumb2_ok } */ + +int +foo1 (int a) +{ + return a | 0xffffff00; +} + +/* { dg-final { scan-assembler "orn.*#255" } } */ + +int +foo2 (int a) +{ + return a & 0xffeeffee; +} + +/* { dg-final { scan-assembler "bic.*#1114129" } } */ + +int +foo3 (int a) +{ + return a & 0xaaaaaa00; +} + +/* { dg-final { scan-assembler "and.*#-1431655766" } } */ +/* { dg-final { scan-assembler "bic.*#170" } } */ --- /dev/null +++ b/gcc/testsuite/gcc.target/arm/thumb2-replicated-constant4.c @@ -0,0 +1,22 @@ +/* Ensure replicated constants don't make things worse. */ +/* { dg-options "-mthumb -O2" } */ +/* { dg-require-effective-target arm_thumb2_ok } */ + +int +foo1 (int a) +{ + /* It might be tempting to use 0x01000100, but it wouldn't help. */ + return a + 0x01f001e0; +} + +/* { dg-final { scan-assembler "add.*#32505856" } } */ +/* { dg-final { scan-assembler "add.*#480" } } */ + +int +foo2 (int a) +{ + return a + 0x0f100e10; +} + +/* { dg-final { scan-assembler "add.*#252706816" } } */ +/* { dg-final { scan-assembler "add.*#3600" } } */