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products/sources/formale Sprachen/Java/Openjdk/src/hotspot/cpu/ppc/ (Sun/Oracle ^©) Datei vom 13.11.2022 mit Größe 21 kB

Quelle c2_MacroAssembler_ppc.cpp Sprache: C

/*
* Copyright (c) 2020, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/

#include "precompiled.hpp"
#include "asm/assembler.hpp"
#include "asm/assembler.inline.hpp"
#include "opto/c2_MacroAssembler.hpp"
#include "opto/intrinsicnode.hpp"
#include "runtime/vm_version.hpp"

#ifdef PRODUCT
#define BLOCK_COMMENT(str) // nothing
#else
#define BLOCK_COMMENT(str) block_comment(str)
#endif
#define BIND(label) bind(label); BLOCK_COMMENT(#label ":")

// Intrinsics for CompactStrings

// Compress char[] to byte[] by compressing 16 bytes at once.
void C2_MacroAssembler::string_compress_16(Register src, Register dst, Register cnt,
                                           Register tmp1, Register tmp2, Register tmp3, Register tmp4, Register tmp5,
                                           Label& Lfailure, bool ascii) {

  const Register tmp0 = R0;
  const int byte_mask = ascii ? 0x7F : 0xFF;
  assert_different_registers(src, dst, cnt, tmp0, tmp1, tmp2, tmp3, tmp4, tmp5);
  Label Lloop, Lslow;

  // Check if cnt >= 8 (= 16 bytes)
  lis(tmp1, byte_mask);           // tmp1 = 0x00FF00FF00FF00FF (non ascii case)
  srwi_(tmp2, cnt, 3);
  beq(CCR0, Lslow);
  ori(tmp1, tmp1, byte_mask);
  rldimi(tmp1, tmp1, 32, 0);
  mtctr(tmp2);

  // 2x unrolled loop
  bind(Lloop);
  ld(tmp2, 0, src);               // _0_1_2_3 (Big Endian)
  ld(tmp4, 8, src);               // _4_5_6_7

  orr(tmp0, tmp2, tmp4);
  rldicl(tmp3, tmp2, 6*8, 64-24); // _____1_2
  rldimi(tmp2, tmp2, 2*8, 2*8);   // _0_2_3_3
  rldicl(tmp5, tmp4, 6*8, 64-24); // _____5_6
  rldimi(tmp4, tmp4, 2*8, 2*8);   // _4_6_7_7

  andc_(tmp0, tmp0, tmp1);
  bne(CCR0, Lfailure);            // Not latin1/ascii.
  addi(src, src, 16);

  rlwimi(tmp3, tmp2, 0*8, 24, 31);// _____1_3
  srdi(tmp2, tmp2, 3*8);          // ____0_2_
  rlwimi(tmp5, tmp4, 0*8, 24, 31);// _____5_7
  srdi(tmp4, tmp4, 3*8);          // ____4_6_

  orr(tmp2, tmp2, tmp3);          // ____0123
  orr(tmp4, tmp4, tmp5);          // ____4567

  stw(tmp2, 0, dst);
  stw(tmp4, 4, dst);
  addi(dst, dst, 8);
  bdnz(Lloop);

  bind(Lslow);                    // Fallback to slow version
}

// Compress char[] to byte[]. cnt must be positive int.
void C2_MacroAssembler::string_compress(Register src, Register dst, Register cnt, Register tmp,
                                        Label& Lfailure, bool ascii) {
  const int byte_mask = ascii ? 0x7F : 0xFF;
  Label Lloop;
  mtctr(cnt);

  bind(Lloop);
  lhz(tmp, 0, src);
  cmplwi(CCR0, tmp, byte_mask);
  bgt(CCR0, Lfailure);            // Not latin1/ascii.
  addi(src, src, 2);
  stb(tmp, 0, dst);
  addi(dst, dst, 1);
  bdnz(Lloop);
}

void C2_MacroAssembler::encode_iso_array(Register src, Register dst, Register len,
                                         Register tmp1, Register tmp2, Register tmp3, Register tmp4, Register tmp5,
                                         Register result, bool ascii) {
  Label Lslow, Lfailure1, Lfailure2, Ldone;

  string_compress_16(src, dst, len, tmp1, tmp2, tmp3, tmp4, tmp5, Lfailure1, ascii);
  rldicl_(result, len, 0, 64-3); // Remaining characters.
  beq(CCR0, Ldone);
  bind(Lslow);
  string_compress(src, dst, result, tmp2, Lfailure2, ascii);
  li(result, 0);
  b(Ldone);

  bind(Lfailure1);
  mr(result, len);
  mfctr(tmp1);
  rldimi_(result, tmp1, 3, 0); // Remaining characters.
  beq(CCR0, Ldone);
  b(Lslow);

  bind(Lfailure2);
  mfctr(result); // Remaining characters.

  bind(Ldone);
  subf(result, result, len);
}

// Inflate byte[] to char[] by inflating 16 bytes at once.
void C2_MacroAssembler::string_inflate_16(Register src, Register dst, Register cnt,
                                          Register tmp1, Register tmp2, Register tmp3, Register tmp4, Register tmp5) {
  const Register tmp0 = R0;
  assert_different_registers(src, dst, cnt, tmp0, tmp1, tmp2, tmp3, tmp4, tmp5);
  Label Lloop, Lslow;

  // Check if cnt >= 8
  srwi_(tmp2, cnt, 3);
  beq(CCR0, Lslow);
  lis(tmp1, 0xFF);                // tmp1 = 0x00FF00FF
  ori(tmp1, tmp1, 0xFF);
  mtctr(tmp2);

  // 2x unrolled loop
  bind(Lloop);
  lwz(tmp2, 0, src);              // ____0123 (Big Endian)
  lwz(tmp4, 4, src);              // ____4567
  addi(src, src, 8);

  rldicl(tmp3, tmp2, 7*8, 64-8);  // _______2
  rlwimi(tmp2, tmp2, 3*8, 16, 23);// ____0113
  rldicl(tmp5, tmp4, 7*8, 64-8);  // _______6
  rlwimi(tmp4, tmp4, 3*8, 16, 23);// ____4557

  andc(tmp0, tmp2, tmp1);         // ____0_1_
  rlwimi(tmp2, tmp3, 2*8, 0, 23); // _____2_3
  andc(tmp3, tmp4, tmp1);         // ____4_5_
  rlwimi(tmp4, tmp5, 2*8, 0, 23); // _____6_7

  rldimi(tmp2, tmp0, 3*8, 0*8);   // _0_1_2_3
  rldimi(tmp4, tmp3, 3*8, 0*8);   // _4_5_6_7

  std(tmp2, 0, dst);
  std(tmp4, 8, dst);
  addi(dst, dst, 16);
  bdnz(Lloop);

  bind(Lslow);                    // Fallback to slow version
}

// Inflate byte[] to char[]. cnt must be positive int.
void C2_MacroAssembler::string_inflate(Register src, Register dst, Register cnt, Register tmp) {
  Label Lloop;
  mtctr(cnt);

  bind(Lloop);
  lbz(tmp, 0, src);
  addi(src, src, 1);
  sth(tmp, 0, dst);
  addi(dst, dst, 2);
  bdnz(Lloop);
}

void C2_MacroAssembler::string_compare(Register str1, Register str2,
                                       Register cnt1, Register cnt2,
                                       Register tmp1, Register result, int ae) {
  const Register tmp0 = R0,
                 diff = tmp1;

  assert_different_registers(str1, str2, cnt1, cnt2, tmp0, tmp1, result);
  Label Ldone, Lslow, Lloop, Lreturn_diff;

  // Note: Making use of the fact that compareTo(a, b) == -compareTo(b, a)
  // we interchange str1 and str2 in the UL case and negate the result.
  // Like this, str1 is always latin1 encoded, except for the UU case.
  // In addition, we need 0 (or sign which is 0) extend.

  if (ae == StrIntrinsicNode::UU) {
    srwi(cnt1, cnt1, 1);
  } else {
    clrldi(cnt1, cnt1, 32);
  }

  if (ae != StrIntrinsicNode::LL) {
    srwi(cnt2, cnt2, 1);
  } else {
    clrldi(cnt2, cnt2, 32);
  }

  // See if the lengths are different, and calculate min in cnt1.
  // Save diff in case we need it for a tie-breaker.
  subf_(diff, cnt2, cnt1); // diff = cnt1 - cnt2
  // if (diff > 0) { cnt1 = cnt2; }
  if (VM_Version::has_isel()) {
    isel(cnt1, CCR0, Assembler::greater, /*invert*/ false, cnt2);
  } else {
    Label Lskip;
    blt(CCR0, Lskip);
    mr(cnt1, cnt2);
    bind(Lskip);
  }

  // Rename registers
  Register chr1 = result;
  Register chr2 = tmp0;

  // Compare multiple characters in fast loop (only implemented for same encoding).
  int stride1 = 8, stride2 = 8;
  if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {
    int log2_chars_per_iter = (ae == StrIntrinsicNode::LL) ? 3 : 2;
    Label Lfastloop, Lskipfast;

    srwi_(tmp0, cnt1, log2_chars_per_iter);
    beq(CCR0, Lskipfast);
    rldicl(cnt2, cnt1, 0, 64 - log2_chars_per_iter); // Remaining characters.
    li(cnt1, 1 << log2_chars_per_iter); // Initialize for failure case: Rescan characters from current iteration.
    mtctr(tmp0);

    bind(Lfastloop);
    ld(chr1, 0, str1);
    ld(chr2, 0, str2);
    cmpd(CCR0, chr1, chr2);
    bne(CCR0, Lslow);
    addi(str1, str1, stride1);
    addi(str2, str2, stride2);
    bdnz(Lfastloop);
    mr(cnt1, cnt2); // Remaining characters.
    bind(Lskipfast);
  }

  // Loop which searches the first difference character by character.
  cmpwi(CCR0, cnt1, 0);
  beq(CCR0, Lreturn_diff);
  bind(Lslow);
  mtctr(cnt1);

  switch (ae) {
    case StrIntrinsicNode::LL: stride1 = 1; stride2 = 1; break;
    case StrIntrinsicNode::UL: // fallthru (see comment above)
    case StrIntrinsicNode::LU: stride1 = 1; stride2 = 2; break;
    case StrIntrinsicNode::UU: stride1 = 2; stride2 = 2; break;
    default: ShouldNotReachHere(); break;
  }

  bind(Lloop);
  if (stride1 == 1) { lbz(chr1, 0, str1); } else { lhz(chr1, 0, str1); }
  if (stride2 == 1) { lbz(chr2, 0, str2); } else { lhz(chr2, 0, str2); }
  subf_(result, chr2, chr1); // result = chr1 - chr2
  bne(CCR0, Ldone);
  addi(str1, str1, stride1);
  addi(str2, str2, stride2);
  bdnz(Lloop);

  // If strings are equal up to min length, return the length difference.
  bind(Lreturn_diff);
  mr(result, diff);

  // Otherwise, return the difference between the first mismatched chars.
  bind(Ldone);
  if (ae == StrIntrinsicNode::UL) {
    neg(result, result); // Negate result (see note above).
  }
}

void C2_MacroAssembler::array_equals(bool is_array_equ, Register ary1, Register ary2,
                                     Register limit, Register tmp1, Register result, bool is_byte) {
  const Register tmp0 = R0;
  assert_different_registers(ary1, ary2, limit, tmp0, tmp1, result);
  Label Ldone, Lskiploop, Lloop, Lfastloop, Lskipfast;
  bool limit_needs_shift = false;

  if (is_array_equ) {
    const int length_offset = arrayOopDesc::length_offset_in_bytes();
    const int base_offset   = arrayOopDesc::base_offset_in_bytes(is_byte ? T_BYTE : T_CHAR);

    // Return true if the same array.
    cmpd(CCR0, ary1, ary2);
    beq(CCR0, Lskiploop);

    // Return false if one of them is NULL.
    cmpdi(CCR0, ary1, 0);
    cmpdi(CCR1, ary2, 0);
    li(result, 0);
    cror(CCR0, Assembler::equal, CCR1, Assembler::equal);
    beq(CCR0, Ldone);

    // Load the lengths of arrays.
    lwz(limit, length_offset, ary1);
    lwz(tmp0, length_offset, ary2);

    // Return false if the two arrays are not equal length.
    cmpw(CCR0, limit, tmp0);
    bne(CCR0, Ldone);

    // Load array addresses.
    addi(ary1, ary1, base_offset);
    addi(ary2, ary2, base_offset);
  } else {
    limit_needs_shift = !is_byte;
    li(result, 0); // Assume not equal.
  }

  // Rename registers
  Register chr1 = tmp0;
  Register chr2 = tmp1;

  // Compare 8 bytes per iteration in fast loop.
  const int log2_chars_per_iter = is_byte ? 3 : 2;

  srwi_(tmp0, limit, log2_chars_per_iter + (limit_needs_shift ? 1 : 0));
  beq(CCR0, Lskipfast);
  mtctr(tmp0);

  bind(Lfastloop);
  ld(chr1, 0, ary1);
  ld(chr2, 0, ary2);
  addi(ary1, ary1, 8);
  addi(ary2, ary2, 8);
  cmpd(CCR0, chr1, chr2);
  bne(CCR0, Ldone);
  bdnz(Lfastloop);

  bind(Lskipfast);
  rldicl_(limit, limit, limit_needs_shift ? 64 - 1 : 0, 64 - log2_chars_per_iter); // Remaining characters.
  beq(CCR0, Lskiploop);
  mtctr(limit);

  // Character by character.
  bind(Lloop);
  if (is_byte) {
    lbz(chr1, 0, ary1);
    lbz(chr2, 0, ary2);
    addi(ary1, ary1, 1);
    addi(ary2, ary2, 1);
  } else {
    lhz(chr1, 0, ary1);
    lhz(chr2, 0, ary2);
    addi(ary1, ary1, 2);
    addi(ary2, ary2, 2);
  }
  cmpw(CCR0, chr1, chr2);
  bne(CCR0, Ldone);
  bdnz(Lloop);

  bind(Lskiploop);
  li(result, 1); // All characters are equal.
  bind(Ldone);
}

void C2_MacroAssembler::string_indexof(Register result, Register haystack, Register haycnt,
                                       Register needle, ciTypeArray* needle_values, Register needlecnt, int needlecntval,
                                       Register tmp1, Register tmp2, Register tmp3, Register tmp4, int ae) {

  // Ensure 0<needlecnt<=haycnt in ideal graph as prerequisite!
  Label L_TooShort, L_Found, L_NotFound, L_End;
  Register last_addr = haycnt, // Kill haycnt at the beginning.
  addr      = tmp1,
  n_start   = tmp2,
  ch1       = tmp3,
  ch2       = R0;

  assert(ae != StrIntrinsicNode::LU, "Invalid encoding");
  const int h_csize = (ae == StrIntrinsicNode::LL) ? 1 : 2;
  const int n_csize = (ae == StrIntrinsicNode::UU) ? 2 : 1;

  // **************************************************************************************************
  // Prepare for main loop: optimized for needle count >=2, bail out otherwise.
  // **************************************************************************************************

  // Compute last haystack addr to use if no match gets found.
  clrldi(haycnt, haycnt, 32);         // Ensure positive int is valid as 64 bit value.
  addi(addr, haystack, -h_csize);     // Accesses use pre-increment.
  if (needlecntval == 0) { // variable needlecnt
   cmpwi(CCR6, needlecnt, 2);
   clrldi(needlecnt, needlecnt, 32);  // Ensure positive int is valid as 64 bit value.
   blt(CCR6, L_TooShort);             // Variable needlecnt: handle short needle separately.
  }

  if (n_csize == 2) { lwz(n_start, 0, needle); } else { lhz(n_start, 0, needle); } // Load first 2 characters of needle.

  if (needlecntval == 0) { // variable needlecnt
   subf(ch1, needlecnt, haycnt);      // Last character index to compare is haycnt-needlecnt.
   addi(needlecnt, needlecnt, -2);    // Rest of needle.
  } else { // constant needlecnt
  guarantee(needlecntval != 1, "IndexOf with single-character needle must be handled separately");
  assert((needlecntval & 0x7fff) == needlecntval, "wrong immediate");
   addi(ch1, haycnt, -needlecntval);  // Last character index to compare is haycnt-needlecnt.
   if (needlecntval > 3) { li(needlecnt, needlecntval - 2); } // Rest of needle.
  }

  if (h_csize == 2) { slwi(ch1, ch1, 1); } // Scale to number of bytes.

  if (ae ==StrIntrinsicNode::UL) {
   srwi(tmp4, n_start, 1*8);          // ___0
   rlwimi(n_start, tmp4, 2*8, 0, 23); // _0_1
  }

  add(last_addr, haystack, ch1);      // Point to last address to compare (haystack+2*(haycnt-needlecnt)).

  // Main Loop (now we have at least 2 characters).
  Label L_OuterLoop, L_InnerLoop, L_FinalCheck, L_Comp1, L_Comp2;
  bind(L_OuterLoop); // Search for 1st 2 characters.
  Register addr_diff = tmp4;
   subf(addr_diff, addr, last_addr);  // Difference between already checked address and last address to check.
   addi(addr, addr, h_csize);         // This is the new address we want to use for comparing.
   srdi_(ch2, addr_diff, h_csize);
   beq(CCR0, L_FinalCheck);           // 2 characters left?
   mtctr(ch2);                        // num of characters / 2
  bind(L_InnerLoop);                  // Main work horse (2x unrolled search loop)
   if (h_csize == 2) {                // Load 2 characters of haystack (ignore alignment).
    lwz(ch1, 0, addr);
    lwz(ch2, 2, addr);
   } else {
    lhz(ch1, 0, addr);
    lhz(ch2, 1, addr);
   }
   cmpw(CCR0, ch1, n_start);          // Compare 2 characters (1 would be sufficient but try to reduce branches to CompLoop).
   cmpw(CCR1, ch2, n_start);
   beq(CCR0, L_Comp1);                // Did we find the needle start?
   beq(CCR1, L_Comp2);
   addi(addr, addr, 2 * h_csize);
   bdnz(L_InnerLoop);
  bind(L_FinalCheck);
   andi_(addr_diff, addr_diff, h_csize); // Remaining characters not covered by InnerLoop: (num of characters) & 1.
   beq(CCR0, L_NotFound);
   if (h_csize == 2) { lwz(ch1, 0, addr); } else { lhz(ch1, 0, addr); } // One position left at which we have to compare.
   cmpw(CCR1, ch1, n_start);
   beq(CCR1, L_Comp1);
  bind(L_NotFound);
   li(result, -1);                    // not found
   b(L_End);

   // **************************************************************************************************
   // Special Case: unfortunately, the variable needle case can be called with needlecnt<2
   // **************************************************************************************************
  if (needlecntval == 0) {           // We have to handle these cases separately.
  Label L_OneCharLoop;
  bind(L_TooShort);
   mtctr(haycnt);
   if (n_csize == 2) { lhz(n_start, 0, needle); } else { lbz(n_start, 0, needle); } // First character of needle
  bind(L_OneCharLoop);
   if (h_csize == 2) { lhzu(ch1, 2, addr); } else { lbzu(ch1, 1, addr); }
   cmpw(CCR1, ch1, n_start);
   beq(CCR1, L_Found);               // Did we find the one character needle?
   bdnz(L_OneCharLoop);
   li(result, -1);                   // Not found.
   b(L_End);
  }

  // **************************************************************************************************
  // Regular Case Part II: compare rest of needle (first 2 characters have been compared already)
  // **************************************************************************************************

  // Compare the rest
  bind(L_Comp2);
   addi(addr, addr, h_csize);        // First comparison has failed, 2nd one hit.
  bind(L_Comp1);                     // Addr points to possible needle start.
  if (needlecntval != 2) {           // Const needlecnt==2?
   if (needlecntval != 3) {
    if (needlecntval == 0) { beq(CCR6, L_Found); } // Variable needlecnt==2?
    Register n_ind = tmp4,
             h_ind = n_ind;
    li(n_ind, 2 * n_csize);          // First 2 characters are already compared, use index 2.
    mtctr(needlecnt);                // Decremented by 2, still > 0.
   Label L_CompLoop;
   bind(L_CompLoop);
    if (ae ==StrIntrinsicNode::UL) {
      h_ind = ch1;
      sldi(h_ind, n_ind, 1);
    }
    if (n_csize == 2) { lhzx(ch2, needle, n_ind); } else { lbzx(ch2, needle, n_ind); }
    if (h_csize == 2) { lhzx(ch1, addr, h_ind); } else { lbzx(ch1, addr, h_ind); }
    cmpw(CCR1, ch1, ch2);
    bne(CCR1, L_OuterLoop);
    addi(n_ind, n_ind, n_csize);
    bdnz(L_CompLoop);
   } else { // No loop required if there's only one needle character left.
    if (n_csize == 2) { lhz(ch2, 2 * 2, needle); } else { lbz(ch2, 2 * 1, needle); }
    if (h_csize == 2) { lhz(ch1, 2 * 2, addr); } else { lbz(ch1, 2 * 1, addr); }
    cmpw(CCR1, ch1, ch2);
    bne(CCR1, L_OuterLoop);
   }
  }
  // Return index ...
  bind(L_Found);
   subf(result, haystack, addr);     // relative to haystack, ...
   if (h_csize == 2) { srdi(result, result, 1); } // in characters.
  bind(L_End);
} // string_indexof

void C2_MacroAssembler::string_indexof_char(Register result, Register haystack, Register haycnt,
                                            Register needle, jchar needleChar, Register tmp1, Register tmp2, bool is_byte) {
  assert_different_registers(haystack, haycnt, needle, tmp1, tmp2);

  Label L_InnerLoop, L_FinalCheck, L_Found1, L_Found2, L_NotFound, L_End;
  Register addr = tmp1,
           ch1 = tmp2,
           ch2 = R0;

  const int h_csize = is_byte ? 1 : 2;

//4:
   srwi_(tmp2, haycnt, 1);   // Shift right by exact_log2(UNROLL_FACTOR).
   mr(addr, haystack);
   beq(CCR0, L_FinalCheck);
   mtctr(tmp2);              // Move to count register.
//8:
  bind(L_InnerLoop);         // Main work horse (2x unrolled search loop).
   if (!is_byte) {
    lhz(ch1, 0, addr);
    lhz(ch2, 2, addr);
   } else {
    lbz(ch1, 0, addr);
    lbz(ch2, 1, addr);
   }
   (needle != R0) ? cmpw(CCR0, ch1, needle) : cmplwi(CCR0, ch1, (unsigned int)needleChar);
   (needle != R0) ? cmpw(CCR1, ch2, needle) : cmplwi(CCR1, ch2, (unsigned int)needleChar);
   beq(CCR0, L_Found1);      // Did we find the needle?
   beq(CCR1, L_Found2);
   addi(addr, addr, 2 * h_csize);
   bdnz(L_InnerLoop);
//16:
  bind(L_FinalCheck);
   andi_(R0, haycnt, 1);
   beq(CCR0, L_NotFound);
   if (!is_byte) { lhz(ch1, 0, addr); } else { lbz(ch1, 0, addr); } // One position left at which we have to compare.
   (needle != R0) ? cmpw(CCR1, ch1, needle) : cmplwi(CCR1, ch1, (unsigned int)needleChar);
   beq(CCR1, L_Found1);
//21:
  bind(L_NotFound);
   li(result, -1);           // Not found.
   b(L_End);

  bind(L_Found2);
   addi(addr, addr, h_csize);
//24:
  bind(L_Found1);            // Return index ...
   subf(result, haystack, addr); // relative to haystack, ...
   if (!is_byte) { srdi(result, result, 1); } // in characters.
  bind(L_End);
} // string_indexof_char

void C2_MacroAssembler::count_positives(Register src, Register cnt, Register result,
                                        Register tmp1, Register tmp2) {
  const Register tmp0 = R0;
  assert_different_registers(src, result, cnt, tmp0, tmp1, tmp2);
  Label Lfastloop, Lslow, Lloop, Ldone;

  // Check if cnt >= 8 (= 16 bytes)
  lis(tmp1, (int)(short)0x8080);  // tmp1 = 0x8080808080808080
  srwi_(tmp2, cnt, 4);
  mr(result, src);                // Use result reg to point to the current position.
  beq(CCR0, Lslow);
  ori(tmp1, tmp1, 0x8080);
  rldimi(tmp1, tmp1, 32, 0);
  mtctr(tmp2);

  // 2x unrolled loop
  bind(Lfastloop);
  ld(tmp2, 0, result);
  ld(tmp0, 8, result);

  orr(tmp0, tmp2, tmp0);

  and_(tmp0, tmp0, tmp1);
  bne(CCR0, Lslow);               // Found negative byte.
  addi(result, result, 16);
  bdnz(Lfastloop);

  bind(Lslow);                    // Fallback to slow version.
  subf(tmp0, src, result);        // Bytes known positive.
  subf_(tmp0, tmp0, cnt);         // Remaining Bytes.
  beq(CCR0, Ldone);
  mtctr(tmp0);
  bind(Lloop);
  lbz(tmp0, 0, result);
  andi_(tmp0, tmp0, 0x80);
  bne(CCR0, Ldone);               // Found negative byte.
  addi(result, result, 1);
  bdnz(Lloop);

  bind(Ldone);
  subf(result, src, result);      // Result is offset from src.
}

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