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[libc] Improve memcpy copy loop

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Rewriting loop so the terminating condition does not depend on the loop body

Differential Revision: https://reviews.llvm.org/D91976
This commit is contained in:
Guillaume Chatelet
2020-11-23 17:30:39 +00:00
parent ec6c5e920a
commit 699d17d4d6
2 changed files with 32 additions and 5 deletions
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7
libc/src/string/memory_utils/memcpy_utils.h
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@@ -90,9 +90,10 @@ static void CopyAlignedBlocks(char *__restrict dst, const char *__restrict src,
CopyBlock<kBlockSize>(dst, src); // Copy first block
// Copy aligned blocks
size_t offset = kBlockSize - offset_from_last_aligned<kBlockSize>(dst);
for (; offset + kBlockSize < count; offset += kBlockSize)
CopyBlock<kBlockSize>(dst + offset, src + offset);
const size_t ofla = offset_from_last_aligned<kBlockSize>(dst);
const size_t limit = count + ofla - kBlockSize;
for (size_t offset = kBlockSize; offset < limit; offset += kBlockSize)
CopyBlock<kBlockSize>(dst - ofla + offset, src - ofla + offset);
CopyLastBlock<kBlockSize>(dst, src, count); // Copy last block
}

30
libc/test/src/string/memory_utils/memcpy_utils_test.cpp
View File

@@ -162,7 +162,23 @@ TEST(MemcpyUtilsTest, CopyBlockOverlap) {
TEST(MemcpyUtilsTest, CopyAlignedBlocks) {
auto &trace = GetTrace();
// Destination is aligned already.
// Destination is aligned and multiple of alignment.
// "1111"
trace.Clear();
CopyAlignedBlocks<4>(I(0), I(0), 4);
EXPECT_STREQ(trace.Write(), "2222");
EXPECT_STREQ(trace.Read(), "2222");
// Destination is aligned and multiple of alignment.
// "11110000"
// + "00001111"
// = "11111111"
trace.Clear();
CopyAlignedBlocks<4>(I(0), I(0), 8);
EXPECT_STREQ(trace.Write(), "11111111");
EXPECT_STREQ(trace.Read(), "11111111");
// Destination is aligned already overlap at end.
// "1111000000000"
// + "0000111100000"
// + "0000000011110"
@@ -173,7 +189,7 @@ TEST(MemcpyUtilsTest, CopyAlignedBlocks) {
EXPECT_STREQ(trace.Write(), "1111111112221");
EXPECT_STREQ(trace.Read(), "1111111112221");
// Misaligned destination
// Misaligned destination.
// "01111000000000"
// + "00001111000000"
// + "00000000111100"
@@ -183,6 +199,16 @@ TEST(MemcpyUtilsTest, CopyAlignedBlocks) {
CopyAlignedBlocks<4>(I(1), I(0), 13);
EXPECT_STREQ(trace.Write(), "01112111112211");
EXPECT_STREQ(trace.Read(), "1112111112211");
// Misaligned destination aligned at end.
// "011110000000"
// + "000011110000"
// + "000000001111"
// = "011121111111"
trace.Clear();
CopyAlignedBlocks<4>(I(1), I(0), 11);
EXPECT_STREQ(trace.Write(), "011121111111");
EXPECT_STREQ(trace.Read(), "11121111111");
}
TEST(MemcpyUtilsTest, MaxReloads) {