mirror of https://git.tukaani.org/xz.git
liblzma: RISC-V filter: Use byte-by-byte access.
Not all RISC-V processors support fast unaligned access so it's better to read only one byte in the main loop. This can be faster even on x86-64 when compared to reading 32 bits at a time as half the time the address is only 16-bit aligned. The downside is larger code size on archs that do support fast unaligned access.
This commit is contained in:
Lasse Collin
Jia Tan
parent
db5eb5f563
commit
50255feeaa
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@ -370,28 +370,59 @@ riscv_encode(void *simple lzma_attribute((__unused__)),
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// The loop is advanced by 2 bytes every iteration since the
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// instruction stream may include 16-bit instructions (C extension).
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for (i = 0; i <= size; i += 2) {
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uint32_t inst = read32le(buffer + i);
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uint32_t inst = buffer[i];
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if (inst == 0xEF) {
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// JAL
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const uint32_t b1 = buffer[i + 1];
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// Only filter rd=x1(ra) and rd=x5(t0).
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if ((b1 & 0x0D) != 0)
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continue;
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if ((inst & 0xDFF) == 0x0EF) {
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// JAL with rd=x1(ra) or rd=x5(t0)
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//
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// The 20-bit immediate is in four pieces.
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// The encoder stores it in big endian form
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// since it improves compression slightly.
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uint32_t addr
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= ((inst & 0x80000000) >> 11)
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| ((inst & 0x7FE00000) >> 20)
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| ((inst & 0x00100000) >> 9)
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| (inst & 0x000FF000);
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const uint32_t b2 = buffer[i + 2];
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const uint32_t b3 = buffer[i + 3];
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const uint32_t pc = now_pos + (uint32_t)i;
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addr += now_pos + (uint32_t)i;
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// The following chart shows the highest three bytes of JAL, focusing on
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// the 20-bit immediate field [31:12]. The first row of numbers is the
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// bit position in a 32-bit little endian instruction. The second row of
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// numbers shows the order of the immediate field in a J-type instruction.
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// The last row is the bit number in each byte.
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//
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// To determine the amount to shift each bit, subtract the value in
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// the last row from the value in the second last row. If the number
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// is positive, shift left. If negative, shift right.
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//
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// For example, at the rightmost side of the chart, the bit 4 in b1 is
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// the bit 12 of the address. Thus that bit needs to be shifted left
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// by 12 - 4 = 8 bits to put it in the right place in the addr variable.
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//
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// NOTE: The immediate of a J-type instruction holds bits [20:1] of
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// the address. The bit [0] is always 0 and not part of the immediate.
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//
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// | b3 | b2 | b1 |
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// | 31 30 29 28 27 26 25 24 | 23 22 21 20 19 18 17 16 | 15 14 13 12 x x x x |
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// | 20 10 9 8 7 6 5 4 | 3 2 1 11 19 18 17 16 | 15 14 13 12 x x x x |
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// | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | 7 6 5 4 x x x x |
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inst = (inst & 0xFFF)
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| ((addr & 0x1E0000) >> 5)
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| ((addr & 0x01FE00) << 7)
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| ((addr & 0x0001FE) << 23);
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uint32_t addr = ((b1 & 0xF0) << 8)
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| ((b2 & 0x0F) << 16)
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| ((b2 & 0x10) << 7)
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| ((b2 & 0xE0) >> 4)
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| ((b3 & 0x7F) << 4)
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| ((b3 & 0x80) << 13);
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write32le(buffer + i, inst);
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addr += pc;
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buffer[i + 1] = (uint8_t)((b1 & 0x0F)
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| ((addr >> 13) & 0xF0));
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buffer[i + 2] = (uint8_t)(addr >> 9);
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buffer[i + 3] = (uint8_t)(addr >> 1);
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// The "-2" is included because the for-loop will
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// always increment by 2. In this case, we want to
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@ -401,7 +432,10 @@ riscv_encode(void *simple lzma_attribute((__unused__)),
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} else if ((inst & 0x7F) == 0x17) {
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// AUIPC
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//
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inst |= (uint32_t)buffer[i + 1] << 8;
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inst |= (uint32_t)buffer[i + 2] << 16;
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inst |= (uint32_t)buffer[i + 3] << 24;
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// Branch based on AUIPC's rd. The bitmask test does
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// the same thing as this:
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//
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@ -587,30 +621,50 @@ riscv_decode(void *simple lzma_attribute((__unused__)),
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size_t i;
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for (i = 0; i <= size; i += 2) {
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uint32_t inst = read32le(buffer + i);
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uint32_t inst = buffer[i];
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if ((inst & 0xDFF) == 0x0EF) {
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// JAL with rd=x1(ra) or rd=x5(t0)
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uint32_t addr
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= ((inst << 5) & 0x1E0000)
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| ((inst >> 7) & 0x01FE00)
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| ((inst >> 23) & 0x0001FE);
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if (inst == 0xEF) {
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// JAL
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const uint32_t b1 = buffer[i + 1];
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addr -= now_pos + (uint32_t)i;
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// Only filter rd=x1(ra) and rd=x5(t0).
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if ((b1 & 0x0D) != 0)
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continue;
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inst = (inst & 0xFFF)
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| ((addr << 11) & 0x80000000)
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| ((addr << 20) & 0x7FE00000)
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| ((addr << 9) & 0x00100000)
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| ( addr & 0x000FF000);
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const uint32_t b2 = buffer[i + 2];
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const uint32_t b3 = buffer[i + 3];
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const uint32_t pc = now_pos + (uint32_t)i;
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// | b3 | b2 | b1 |
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// | 31 30 29 28 27 26 25 24 | 23 22 21 20 19 18 17 16 | 15 14 13 12 x x x x |
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// | 20 10 9 8 7 6 5 4 | 3 2 1 11 19 18 17 16 | 15 14 13 12 x x x x |
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// | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | 7 6 5 4 x x x x |
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uint32_t addr = ((b1 & 0xF0) << 13)
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| (b2 << 9) | (b3 << 1);
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addr -= pc;
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buffer[i + 1] = (uint8_t)((b1 & 0x0F)
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| ((addr >> 8) & 0xF0));
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buffer[i + 2] = (uint8_t)(((addr >> 16) & 0x0F)
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| ((addr >> 7) & 0x10)
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| ((addr << 4) & 0xE0));
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buffer[i + 3] = (uint8_t)(((addr >> 4) & 0x7F)
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| ((addr >> 13) & 0x80));
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write32le(buffer + i, inst);
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i += 4 - 2;
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} else if ((inst & 0x7F) == 0x17) {
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// AUIPC
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uint32_t inst2;
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inst |= (uint32_t)buffer[i + 1] << 8;
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inst |= (uint32_t)buffer[i + 2] << 16;
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inst |= (uint32_t)buffer[i + 3] << 24;
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if (inst & 0xE80) {
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// AUIPC's rd doesn't equal x0 or x2.
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