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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 2024-01-23 00:09:48 +02:00 committed by Jia Tan
parent db5eb5f563
commit 50255feeaa
1 changed files with 84 additions and 30 deletions
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114
src/liblzma/simple/riscv.c
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@ -370,28 +370,59 @@ riscv_encode(void *simple lzma_attribute((__unused__)),
// The loop is advanced by 2 bytes every iteration since the // The loop is advanced by 2 bytes every iteration since the
// instruction stream may include 16-bit instructions (C extension). // instruction stream may include 16-bit instructions (C extension).
for (i = 0; i <= size; i += 2) { for (i = 0; i <= size; i += 2) {
uint32_t inst = read32le(buffer + i); uint32_t inst = buffer[i];
if (inst == 0xEF) {
// JAL
const uint32_t b1 = buffer[i + 1];
// Only filter rd=x1(ra) and rd=x5(t0).
if ((b1 & 0x0D) != 0)
continue;
if ((inst & 0xDFF) == 0x0EF) {
// JAL with rd=x1(ra) or rd=x5(t0)
//
// The 20-bit immediate is in four pieces. // The 20-bit immediate is in four pieces.
// The encoder stores it in big endian form // The encoder stores it in big endian form
// since it improves compression slightly. // since it improves compression slightly.
uint32_t addr const uint32_t b2 = buffer[i + 2];
= ((inst & 0x80000000) >> 11) const uint32_t b3 = buffer[i + 3];
| ((inst & 0x7FE00000) >> 20) const uint32_t pc = now_pos + (uint32_t)i;
| ((inst & 0x00100000) >> 9)
| (inst & 0x000FF000);
addr += now_pos + (uint32_t)i; // The following chart shows the highest three bytes of JAL, focusing on
// the 20-bit immediate field [31:12]. The first row of numbers is the
// bit position in a 32-bit little endian instruction. The second row of
// numbers shows the order of the immediate field in a J-type instruction.
// The last row is the bit number in each byte.
//
// To determine the amount to shift each bit, subtract the value in
// the last row from the value in the second last row. If the number
// is positive, shift left. If negative, shift right.
//
// For example, at the rightmost side of the chart, the bit 4 in b1 is
// the bit 12 of the address. Thus that bit needs to be shifted left
// by 12 - 4 = 8 bits to put it in the right place in the addr variable.
//
// NOTE: The immediate of a J-type instruction holds bits [20:1] of
// the address. The bit [0] is always 0 and not part of the immediate.
//
// | b3 | b2 | b1 |
// | 31 30 29 28 27 26 25 24 | 23 22 21 20 19 18 17 16 | 15 14 13 12 x x x x |
// | 20 10 9 8 7 6 5 4 | 3 2 1 11 19 18 17 16 | 15 14 13 12 x x x x |
// | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | 7 6 5 4 x x x x |
inst = (inst & 0xFFF) uint32_t addr = ((b1 & 0xF0) << 8)
| ((addr & 0x1E0000) >> 5) | ((b2 & 0x0F) << 16)
| ((addr & 0x01FE00) << 7) | ((b2 & 0x10) << 7)
| ((addr & 0x0001FE) << 23); | ((b2 & 0xE0) >> 4)
| ((b3 & 0x7F) << 4)
| ((b3 & 0x80) << 13);
write32le(buffer + i, inst); addr += pc;
buffer[i + 1] = (uint8_t)((b1 & 0x0F)
| ((addr >> 13) & 0xF0));
buffer[i + 2] = (uint8_t)(addr >> 9);
buffer[i + 3] = (uint8_t)(addr >> 1);
// The "-2" is included because the for-loop will // The "-2" is included because the for-loop will
// always increment by 2. In this case, we want to // always increment by 2. In this case, we want to
@ -401,7 +432,10 @@ riscv_encode(void *simple lzma_attribute((__unused__)),
} else if ((inst & 0x7F) == 0x17) { } else if ((inst & 0x7F) == 0x17) {
// AUIPC // AUIPC
// inst |= (uint32_t)buffer[i + 1] << 8;
inst |= (uint32_t)buffer[i + 2] << 16;
inst |= (uint32_t)buffer[i + 3] << 24;
// Branch based on AUIPC's rd. The bitmask test does // Branch based on AUIPC's rd. The bitmask test does
// the same thing as this: // the same thing as this:
// //
@ -587,30 +621,50 @@ riscv_decode(void *simple lzma_attribute((__unused__)),
size_t i; size_t i;
for (i = 0; i <= size; i += 2) { for (i = 0; i <= size; i += 2) {
uint32_t inst = read32le(buffer + i); uint32_t inst = buffer[i];
if ((inst & 0xDFF) == 0x0EF) { if (inst == 0xEF) {
// JAL with rd=x1(ra) or rd=x5(t0) // JAL
uint32_t addr const uint32_t b1 = buffer[i + 1];
= ((inst << 5) & 0x1E0000)
| ((inst >> 7) & 0x01FE00)
| ((inst >> 23) & 0x0001FE);
addr -= now_pos + (uint32_t)i; // Only filter rd=x1(ra) and rd=x5(t0).
if ((b1 & 0x0D) != 0)
continue;
inst = (inst & 0xFFF) const uint32_t b2 = buffer[i + 2];
| ((addr << 11) & 0x80000000) const uint32_t b3 = buffer[i + 3];
| ((addr << 20) & 0x7FE00000) const uint32_t pc = now_pos + (uint32_t)i;
| ((addr << 9) & 0x00100000)
| ( addr & 0x000FF000); // | b3 | b2 | b1 |
// | 31 30 29 28 27 26 25 24 | 23 22 21 20 19 18 17 16 | 15 14 13 12 x x x x |
// | 20 10 9 8 7 6 5 4 | 3 2 1 11 19 18 17 16 | 15 14 13 12 x x x x |
// | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | 7 6 5 4 x x x x |
uint32_t addr = ((b1 & 0xF0) << 13)
| (b2 << 9) | (b3 << 1);
addr -= pc;
buffer[i + 1] = (uint8_t)((b1 & 0x0F)
| ((addr >> 8) & 0xF0));
buffer[i + 2] = (uint8_t)(((addr >> 16) & 0x0F)
| ((addr >> 7) & 0x10)
| ((addr << 4) & 0xE0));
buffer[i + 3] = (uint8_t)(((addr >> 4) & 0x7F)
| ((addr >> 13) & 0x80));
write32le(buffer + i, inst);
i += 4 - 2; i += 4 - 2;
} else if ((inst & 0x7F) == 0x17) { } else if ((inst & 0x7F) == 0x17) {
// AUIPC // AUIPC
uint32_t inst2; uint32_t inst2;
inst |= (uint32_t)buffer[i + 1] << 8;
inst |= (uint32_t)buffer[i + 2] << 16;
inst |= (uint32_t)buffer[i + 3] << 24;
if (inst & 0xE80) { if (inst & 0xE80) {
// AUIPC's rd doesn't equal x0 or x2. // AUIPC's rd doesn't equal x0 or x2.