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SourceManager: Vectorize ComputeLineNumbers for SSE2.

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This method is very hot, it is called when emitting diagnostics, in -E mode
and for many #pragma handlers. It scans through the whole source file to
count newlines, records and caches them in a vector.

The speedup from vectorization isn't very large, as we fall back to bytewise
scanning when we hit a newline. There might be a way to avoid leaving the sse
loop but everything I tried didn't work out because a call to push_back
clobbers xmm registers.

About 2% speedup on average on "clang -E > /dev/null" of all .cpp files in
clang's lib/Sema.

llvm-svn: 154204
This commit is contained in:
Benjamin Kramer
2012-04-06 20:49:55 +00:00
parent d2863dab85
commit 543036a447
1 changed files with 39 additions and 2 deletions
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41
clang/lib/Basic/SourceManager.cpp
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@@ -1037,6 +1037,10 @@ unsigned SourceManager::getPresumedColumnNumber(SourceLocation Loc,
return getPresumedLoc(Loc).getColumn();
}
#ifdef __SSE2__
#include <emmintrin.h>
#endif
static LLVM_ATTRIBUTE_NOINLINE void
ComputeLineNumbers(DiagnosticsEngine &Diag, ContentCache *FI,
llvm::BumpPtrAllocator &Alloc,
@@ -1062,11 +1066,44 @@ static void ComputeLineNumbers(DiagnosticsEngine &Diag, ContentCache *FI,
unsigned Offs = 0;
while (1) {
// Skip over the contents of the line.
// TODO: Vectorize this? This is very performance sensitive for programs
// with lots of diagnostics and in -E mode.
const unsigned char *NextBuf = (const unsigned char *)Buf;
#ifdef __SSE2__
// Try to skip to the next newline using SSE instructions. This is very
// performance sensitive for programs with lots of diagnostics and in -E
// mode.
__m128i CRs = _mm_set1_epi8('\r');
__m128i LFs = _mm_set1_epi8('\n');
// First fix up the alignment to 16 bytes.
while (((uintptr_t)NextBuf & 0xF) != 0) {
if (*NextBuf == '\n' || *NextBuf == '\r' || *NextBuf == '\0')
goto FoundSpecialChar;
++NextBuf;
}
// Scan 16 byte chunks for '\r' and '\n'. Ignore '\0'.
while (NextBuf+16 <= End) {
__m128i Chunk = *(__m128i*)NextBuf;
__m128i Cmp = _mm_or_si128(_mm_cmpeq_epi8(Chunk, CRs),
_mm_cmpeq_epi8(Chunk, LFs));
unsigned Mask = _mm_movemask_epi8(Cmp);
// If we found a newline, adjust the pointer and jump to the handling code.
if (Mask != 0) {
NextBuf += llvm::CountTrailingZeros_32(Mask);
goto FoundSpecialChar;
}
NextBuf += 16;
}
#endif
while (*NextBuf != '\n' && *NextBuf != '\r' && *NextBuf != '\0')
++NextBuf;
#ifdef __SSE2__
FoundSpecialChar:
#endif
Offs += NextBuf-Buf;
Buf = NextBuf;