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+/*
+ * M7memset.S: SPARC M7 optimized memset.
+ *
+ * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ */
+
+/*
+ * M7memset.S: M7 optimized memset.
+ *
+ * char *memset(sp, c, n)
+ *
+ * Set an array of n chars starting at sp to the character c.
+ * Return sp.
+ *
+ * Fast assembler language version of the following C-program for memset
+ * which represents the `standard' for the C-library.
+ *
+ * void *
+ * memset(void *sp1, int c, size_t n)
+ * {
+ * if (n != 0) {
+ * char *sp = sp1;
+ * do {
+ * *sp++ = (char)c;
+ * } while (--n != 0);
+ * }
+ * return (sp1);
+ * }
+ *
+ * The algorithm is as follows :
+ *
+ * For small 6 or fewer bytes stores, bytes will be stored.
+ *
+ * For less than 32 bytes stores, align the address on 4 byte boundary.
+ * Then store as many 4-byte chunks, followed by trailing bytes.
+ *
+ * For sizes greater than 32 bytes, align the address on 8 byte boundary.
+ * if (count >= 64) {
+ * store 8-bytes chunks to align the address on 64 byte boundary
+ * if (value to be set is zero && count >= MIN_ZERO) {
+ * Using BIS stores, set the first long word of each
+ * 64-byte cache line to zero which will also clear the
+ * other seven long words of the cache line.
+ * }
+ * else if (count >= MIN_LOOP) {
+ * Using BIS stores, set the first long word of each of
+ * ST_CHUNK cache lines (64 bytes each) before the main
+ * loop is entered.
+ * In the main loop, continue pre-setting the first long
+ * word of each cache line ST_CHUNK lines in advance while
+ * setting the other seven long words (56 bytes) of each
+ * cache line until fewer than ST_CHUNK*64 bytes remain.
+ * Then set the remaining seven long words of each cache
+ * line that has already had its first long word set.
+ * }
+ * store remaining data in 64-byte chunks until less than
+ * 64 bytes remain.
+ * }
+ * Store as many 8-byte chunks, followed by trailing bytes.
+ *
+ * BIS = Block Init Store
+ * Doing the advance store of the first element of the cache line
+ * initiates the displacement of a cache line while only using a single
+ * instruction in the pipeline. That avoids various pipeline delays,
+ * such as filling the miss buffer. The performance effect is
+ * similar to prefetching for normal stores.
+ * The special case for zero fills runs faster and uses fewer instruction
+ * cycles than the normal memset loop.
+ *
+ * We only use BIS for memset of greater than MIN_LOOP bytes because a sequence
+ * BIS stores must be followed by a membar #StoreStore. The benefit of
+ * the BIS store must be balanced against the cost of the membar operation.
+ */
+
+/*
+ * ASI_STBI_P marks the cache line as "least recently used"
+ * which means if many threads are active, it has a high chance
+ * of being pushed out of the cache between the first initializing
+ * store and the final stores.
+ * Thus, we use ASI_STBIMRU_P which marks the cache line as
+ * "most recently used" for all but the last store to the cache line.
+ */
+
+#include <asm/asi.h>
+#include <asm/page.h>
+
+#define ASI_STBI_P ASI_BLK_INIT_QUAD_LDD_P
+#define ASI_STBIMRU_P ASI_ST_BLKINIT_MRU_P
+
+
+#define ST_CHUNK 24 /* multiple of 4 due to loop unrolling */
+#define MIN_LOOP 16320
+#define MIN_ZERO 512
+
+ .section ".text"
+ .align 32
+
+/*
+ * Define clear_page(dest) as memset(dest, 0, PAGE_SIZE)
+ * (can create a more optimized version later.)
+ */
+ .globl M7clear_page
+ .globl M7clear_user_page
+M7clear_page: /* clear_page(dest) */
+M7clear_user_page:
+ set PAGE_SIZE, %o1
+ /* fall through into bzero code */
+
+ .size M7clear_page,.-M7clear_page
+ .size M7clear_user_page,.-M7clear_user_page
+
+/*
+ * Define bzero(dest, n) as memset(dest, 0, n)
+ * (can create a more optimized version later.)
+ */
+ .globl M7bzero
+M7bzero: /* bzero(dest, size) */
+ mov %o1, %o2
+ mov 0, %o1
+ /* fall through into memset code */
+
+ .size M7bzero,.-M7bzero
+
+ .global M7memset
+ .type M7memset, #function
+ .register %g3, #scratch
+M7memset:
+ mov %o0, %o5 ! copy sp1 before using it
+ cmp %o2, 7 ! if small counts, just write bytes
+ bleu,pn %xcc, .wrchar
+ and %o1, 0xff, %o1 ! o1 is (char)c
+
+ sll %o1, 8, %o3
+ or %o1, %o3, %o1 ! now o1 has 2 bytes of c
+ sll %o1, 16, %o3
+ cmp %o2, 32
+ blu,pn %xcc, .wdalign
+ or %o1, %o3, %o1 ! now o1 has 4 bytes of c
+
+ sllx %o1, 32, %o3
+ or %o1, %o3, %o1 ! now o1 has 8 bytes of c
+
+.dbalign:
+ andcc %o5, 7, %o3 ! is sp1 aligned on a 8 byte bound?
+ bz,pt %xcc, .blkalign ! already long word aligned
+ sub %o3, 8, %o3 ! -(bytes till long word aligned)
+
+ add %o2, %o3, %o2 ! update o2 with new count
+ ! Set -(%o3) bytes till sp1 long word aligned
+1: stb %o1, [%o5] ! there is at least 1 byte to set
+ inccc %o3 ! byte clearing loop
+ bl,pt %xcc, 1b
+ inc %o5
+
+ ! Now sp1 is long word aligned (sp1 is found in %o5)
+.blkalign:
+ cmp %o2, 64 ! check if there are 64 bytes to set
+ blu,pn %xcc, .wrshort
+ mov %o2, %o3
+
+ andcc %o5, 63, %o3 ! is sp1 block aligned?
+ bz,pt %xcc, .blkwr ! now block aligned
+ sub %o3, 64, %o3 ! o3 is -(bytes till block aligned)
+ add %o2, %o3, %o2 ! o2 is the remainder
+
+ ! Store -(%o3) bytes till dst is block (64 byte) aligned.
+ ! Use long word stores.
+ ! Recall that dst is already long word aligned
+1:
+ addcc %o3, 8, %o3
+ stx %o1, [%o5]
+ bl,pt %xcc, 1b
+ add %o5, 8, %o5
+
+ ! Now sp1 is block aligned
+.blkwr:
+ andn %o2, 63, %o4 ! calculate size of blocks in bytes
+ brz,pn %o1, .wrzero ! special case if c == 0
+ and %o2, 63, %o3 ! %o3 = bytes left after blk stores.
+
+ set MIN_LOOP, %g1
+ cmp %o4, %g1 ! check there are enough bytes to set
+ blu,pn %xcc, .short_set ! to justify cost of membar
+ ! must be > pre-cleared lines
+ nop
+
+ ! initial cache-clearing stores
+ ! get store pipeline moving
+ rd %asi, %g3 ! save %asi to be restored later
+ wr %g0, ASI_STBIMRU_P, %asi
+
+ ! Primary memset loop for large memsets
+.wr_loop:
+ sub %o5, 8, %o5 ! adjust %o5 for ASI store alignment
+ mov ST_CHUNK, %g1
+.wr_loop_start:
+ stxa %o1, [%o5+8]%asi
+ subcc %g1, 4, %g1
+ stxa %o1, [%o5+8+64]%asi
+ add %o5, 256, %o5
+ stxa %o1, [%o5+8-128]%asi
+ bgu %xcc, .wr_loop_start
+ stxa %o1, [%o5+8-64]%asi
+
+ sub %o5, ST_CHUNK*64, %o5 ! reset %o5
+ mov ST_CHUNK, %g1
+
+.wr_loop_rest:
+ stxa %o1, [%o5+8+8]%asi
+ sub %o4, 64, %o4
+ stxa %o1, [%o5+16+8]%asi
+ subcc %g1, 1, %g1
+ stxa %o1, [%o5+24+8]%asi
+ stxa %o1, [%o5+32+8]%asi
+ stxa %o1, [%o5+40+8]%asi
+ add %o5, 64, %o5
+ stxa %o1, [%o5-8]%asi
+ bgu %xcc, .wr_loop_rest
+ stxa %o1, [%o5]ASI_STBI_P
+
+ ! If more than ST_CHUNK*64 bytes remain to set, continue
+ ! setting the first long word of each cache line in advance
+ ! to keep the store pipeline moving.
+
+ cmp %o4, ST_CHUNK*64
+ bge,pt %xcc, .wr_loop_start
+ mov ST_CHUNK, %g1
+
+ brz,a,pn %o4, .asi_done
+ add %o5, 8, %o5 ! restore %o5 offset
+
+.wr_loop_small:
+ stxa %o1, [%o5+8]%asi
+ stxa %o1, [%o5+8+8]%asi
+ stxa %o1, [%o5+16+8]%asi
+ stxa %o1, [%o5+24+8]%asi
+ stxa %o1, [%o5+32+8]%asi
+ subcc %o4, 64, %o4
+ stxa %o1, [%o5+40+8]%asi
+ add %o5, 64, %o5
+ stxa %o1, [%o5-8]%asi
+ bgu,pt %xcc, .wr_loop_small
+ stxa %o1, [%o5]ASI_STBI_P
+
+ ba .asi_done
+ add %o5, 8, %o5 ! restore %o5 offset
+
+ ! Special case loop for zero fill memsets
+ ! For each 64 byte cache line, single STBI to first element
+ ! clears line
+.wrzero:
+ cmp %o4, MIN_ZERO ! check if enough bytes to set
+ ! to pay %asi + membar cost
+ blu %xcc, .short_set
+ nop
+ sub %o4, 256, %o4
+
+.wrzero_loop:
+ mov 64, %g3
+ stxa %o1, [%o5]ASI_STBI_P
+ subcc %o4, 256, %o4
+ stxa %o1, [%o5+%g3]ASI_STBI_P
+ add %o5, 256, %o5
+ sub %g3, 192, %g3
+ stxa %o1, [%o5+%g3]ASI_STBI_P
+ add %g3, 64, %g3
+ bge,pt %xcc, .wrzero_loop
+ stxa %o1, [%o5+%g3]ASI_STBI_P
+ add %o4, 256, %o4
+
+ brz,pn %o4, .bsi_done
+ nop
+
+.wrzero_small:
+ stxa %o1, [%o5]ASI_STBI_P
+ subcc %o4, 64, %o4
+ bgu,pt %xcc, .wrzero_small
+ add %o5, 64, %o5
+ ba,a .bsi_done
+
+.asi_done:
+ wr %g3, 0x0, %asi ! restored saved %asi
+.bsi_done:
+ membar #StoreStore ! required by use of Block Store Init
+
+.short_set:
+ cmp %o4, 64 ! check if 64 bytes to set
+ blu %xcc, 5f
+ nop
+4: ! set final blocks of 64 bytes
+ stx %o1, [%o5]
+ stx %o1, [%o5+8]
+ stx %o1, [%o5+16]
+ stx %o1, [%o5+24]
+ subcc %o4, 64, %o4
+ stx %o1, [%o5+32]
+ stx %o1, [%o5+40]
+ add %o5, 64, %o5
+ stx %o1, [%o5-16]
+ bgu,pt %xcc, 4b
+ stx %o1, [%o5-8]
+
+5:
+ ! Set the remaining long words
+.wrshort:
+ subcc %o3, 8, %o3 ! Can we store any long words?
+ blu,pn %xcc, .wrchars
+ and %o2, 7, %o2 ! calc bytes left after long words
+6:
+ subcc %o3, 8, %o3
+ stx %o1, [%o5] ! store the long words
+ bgeu,pt %xcc, 6b
+ add %o5, 8, %o5
+
+.wrchars: ! check for extra chars
+ brnz %o2, .wrfin
+ nop
+ retl
+ nop
+
+.wdalign:
+ andcc %o5, 3, %o3 ! is sp1 aligned on a word boundary
+ bz,pn %xcc, .wrword
+ andn %o2, 3, %o3 ! create word sized count in %o3
+
+ dec %o2 ! decrement count
+ stb %o1, [%o5] ! clear a byte
+ b .wdalign
+ inc %o5 ! next byte
+
+.wrword:
+ subcc %o3, 4, %o3
+ st %o1, [%o5] ! 4-byte writing loop
+ bnz,pt %xcc, .wrword
+ add %o5, 4, %o5
+
+ and %o2, 3, %o2 ! leftover count, if any
+
+.wrchar:
+ ! Set the remaining bytes, if any
+ brz %o2, .exit
+ nop
+.wrfin:
+ deccc %o2
+ stb %o1, [%o5]
+ bgu,pt %xcc, .wrfin
+ inc %o5
+.exit:
+ retl ! %o0 was preserved
+ nop
+
+ .size M7memset,.-M7memset