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Optimized division by constants

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This commit is contained in:
tevador
2019-01-11 14:08:21 +01:00
parent c02ee4291d
commit 451dfc5730
4 changed files with 385 additions and 5 deletions
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99
src/AssemblyGeneratorX86.cpp
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@@ -17,10 +17,14 @@ You should have received a copy of the GNU General Public License
along with RandomX. If not, see<http://www.gnu.org/licenses/>.
*/
//#define TRACE
//#define MAGIC_DIVISION
#include "AssemblyGeneratorX86.hpp"
#include "Pcg32.hpp"
#include "common.hpp"
#include "instructions.hpp"
#ifdef MAGIC_DIVISION
#include "divideByConstantCodegen.h"
#endif
namespace RandomX {
@@ -315,34 +319,118 @@ namespace RandomX {
void AssemblyGeneratorX86::h_DIV_64(Instruction& instr, int i) {
genar(instr, i);
if ((instr.locb & 7) >= 6) {
#ifdef MAGIC_DIVISION
if (instr.imm32 != 0) {
uint32_t divisor = instr.imm32;
asmCode << "\t; magic divide by " << divisor << std::endl;
if (divisor & (divisor - 1)) {
magicu_info mi = compute_unsigned_magic_info(divisor, sizeof(uint64_t) * 8);
if (mi.pre_shift > 0)
asmCode << "\tshr rax, " << mi.pre_shift << std::endl;
if (mi.increment) {
asmCode << "\tadd rax, 1" << std::endl;
asmCode << "\tsbb rax, 0" << std::endl;
}
asmCode << "\tmov rcx, " << mi.multiplier << std::endl;
asmCode << "\tmul rcx" << std::endl;
asmCode << "\tmov rax, rdx" << std::endl;
if (mi.post_shift > 0)
asmCode << "\tshr rax, " << mi.post_shift << std::endl;
}
else { //divisor is a power of two
int shift = 0;
while (divisor >>= 1)
++shift;
if(shift > 0)
asmCode << "\tshr rax, " << shift << std::endl;
}
}
#else
if (instr.imm32 == 0) {
asmCode << "\tmov ecx, 1" << std::endl;
}
else {
asmCode << "\tmov ecx, " << instr.imm32 << std::endl;
}
#endif
}
else {
asmCode << "\tmov ecx, 1" << std::endl;
asmCode << "\tmov edx, " << regR32[instr.regb % RegistersCount] << std::endl;
asmCode << "\ttest edx, edx" << std::endl;
asmCode << "\tcmovne ecx, edx" << std::endl;
#ifdef MAGIC_DIVISION
asmCode << "\txor edx, edx" << std::endl;
asmCode << "\tdiv rcx" << std::endl;
#endif
}
#ifndef MAGIC_DIVISION
asmCode << "\txor edx, edx" << std::endl;
asmCode << "\tdiv rcx" << std::endl;
#endif
gencr(instr);
}
void AssemblyGeneratorX86::h_IDIV_64(Instruction& instr, int i) {
genar(instr, i);
#ifdef MAGIC_DIVISION
if ((instr.locb & 7) >= 6) {
int64_t divisor = instr.imm32;
asmCode << "\t; magic divide by " << divisor << std::endl;
if ((divisor & -divisor) == divisor || (divisor & -divisor) == -divisor) {
// +/- power of two
bool negative = divisor < 0;
if (negative)
divisor = -divisor;
int shift = 0;
uint64_t unsignedDivisor = divisor;
while (unsignedDivisor >>= 1)
++shift;
if (shift > 0) {
asmCode << "\tmov rcx, rax" << std::endl;
asmCode << "\tsar rcx, 63" << std::endl;
uint32_t mask = (1ULL << shift) + 0xFFFFFFFF;
asmCode << "\tand ecx, 0" << std::hex << mask << std::dec << "h" << std::endl;
asmCode << "\tadd rax, rcx" << std::endl;
asmCode << "\tsar rax, " << shift << std::endl;
}
if(negative)
asmCode << "\tneg rax" << std::endl;
} else if(divisor != 0) {
magics_info mi = compute_signed_magic_info(divisor);
if ((divisor >= 0) != (mi.multiplier >= 0))
asmCode << "\tmov rcx, rax" << std::endl;
asmCode << "\tmov rdx, " << mi.multiplier << std::endl;
asmCode << "\timul rdx" << std::endl;
asmCode << "\tmov rax, rdx" << std::endl;
asmCode << "\txor edx, edx" << std::endl;
bool haveSF = false;
if (divisor > 0 && mi.multiplier < 0) {
asmCode << "\tadd rax, rcx" << std::endl;
haveSF = true;
}
if (divisor < 0 && mi.multiplier > 0) {
asmCode << "\tsub rax, rcx" << std::endl;
haveSF = true;
}
if (mi.shift > 0) {
asmCode << "\tsar rax, " << mi.shift << std::endl;
haveSF = true;
}
if (!haveSF)
asmCode << "\ttest rax, rax" << std::endl;
asmCode << "\tsets dl" << std::endl;
asmCode << "\tadd rax, rdx" << std::endl;
}
}
else {
#endif
asmCode << "\tmov edx, ";
genbr132(instr);
asmCode << "\tcmp edx, -1" << std::endl;
asmCode << "\tjne short safe_idiv_" << i << std::endl;
asmCode << "\tmov rcx, rax" << std::endl;
asmCode << "\trol rcx, 1" << std::endl;
asmCode << "\tdec rcx" << std::endl;
asmCode << "\tjz short result_idiv_" << i << std::endl;
asmCode << "\tneg rax" << std::endl;
asmCode << "\tjmp short result_idiv_" << i << std::endl;
asmCode << "safe_idiv_" << i << ":" << std::endl;
asmCode << "\tmov ecx, 1" << std::endl;
asmCode << "\ttest edx, edx" << std::endl;
@@ -351,6 +439,9 @@ namespace RandomX {
asmCode << "\tcqo" << std::endl;
asmCode << "\tidiv rcx" << std::endl;
asmCode << "result_idiv_" << i << ":" << std::endl;
#ifdef MAGIC_DIVISION
}
#endif
gencr(instr);
}