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Preprocessor: Use std::string instead of std::stringstream

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std::stringstream has a measurable overhead for preprocessing - it
appears that operator<< does a tiny bit of extra work for appending
chars/strings and also can't be inlined in most cases on VS2015;
additionally, std::endl triggers a stream flush which also adds up.

Replacing this with std::string buffer gets the preprocessing time down
from 180ms to 135ms in one case, making it 1.33x faster.

Note that integer-to-string conversion is using std::to_string; in
theory this could be slower than sprintf or manual conversion, but I
haven't found these cases to affect preprocessing time in practice
(std::to_string would always use the short string buffer for
line/version numbers, and the number of calls is not too significant).
This commit is contained in:
Arseny Kapoulkine 2018-02-05 16:07:39 -08:00
parent 82ead04c39
commit 75cffdf92c
1 changed files with 37 additions and 28 deletions
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65
glslang/MachineIndependent/ShaderLang.cpp
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@ -912,7 +912,7 @@ bool ProcessDeferred(
class SourceLineSynchronizer {
public:
SourceLineSynchronizer(const std::function<int()>& lastSourceIndex,
std::stringstream* output)
std::string* output)
: getLastSourceIndex(lastSourceIndex), output(output), lastSource(-1), lastLine(0) {}
// SourceLineSynchronizer(const SourceLineSynchronizer&) = delete;
// SourceLineSynchronizer& operator=(const SourceLineSynchronizer&) = delete;
@ -927,7 +927,7 @@ public:
// used. We also need to output a newline to separate the output
// from the previous source string (if there is one).
if (lastSource != -1 || lastLine != 0)
*output << std::endl;
*output += '\n';
lastSource = getLastSourceIndex();
lastLine = -1;
return true;
@ -942,7 +942,7 @@ public:
syncToMostRecentString();
const bool newLineStarted = lastLine < tokenLine;
for (; lastLine < tokenLine; ++lastLine) {
if (lastLine > 0) *output << std::endl;
if (lastLine > 0) *output += '\n';
}
return newLineStarted;
}
@ -956,8 +956,8 @@ private:
// A function for getting the index of the last valid source string we've
// read tokens from.
const std::function<int()> getLastSourceIndex;
// output stream for newlines.
std::stringstream* output;
// output string for newlines.
std::string* output;
// lastSource is the source string index (starting from 0) of the last token
// processed. It is tracked in order for newlines to be inserted when a new
// source string starts. -1 means we haven't started processing any source
@ -988,27 +988,33 @@ struct DoPreprocessing {
parseContext.setScanner(&input);
ppContext.setInput(input, versionWillBeError);
std::stringstream outputStream;
std::string outputBuffer;
SourceLineSynchronizer lineSync(
std::bind(&TInputScanner::getLastValidSourceIndex, &input), &outputStream);
std::bind(&TInputScanner::getLastValidSourceIndex, &input), &outputBuffer);
parseContext.setExtensionCallback([&lineSync, &outputStream](
parseContext.setExtensionCallback([&lineSync, &outputBuffer](
int line, const char* extension, const char* behavior) {
lineSync.syncToLine(line);
outputStream << "#extension " << extension << " : " << behavior;
outputBuffer += "#extension ";
outputBuffer += extension;
outputBuffer += " : ";
outputBuffer += behavior;
});
parseContext.setLineCallback([&lineSync, &outputStream, &parseContext](
parseContext.setLineCallback([&lineSync, &outputBuffer, &parseContext](
int curLineNum, int newLineNum, bool hasSource, int sourceNum, const char* sourceName) {
// SourceNum is the number of the source-string that is being parsed.
lineSync.syncToLine(curLineNum);
outputStream << "#line " << newLineNum;
outputBuffer += "#line ";
outputBuffer += std::to_string(newLineNum);
if (hasSource) {
outputStream << " ";
outputBuffer += ' ';
if (sourceName != nullptr) {
outputStream << "\"" << sourceName << "\"";
outputBuffer += '\"';
outputBuffer += sourceName;
outputBuffer += '\"';
} else {
outputStream << sourceNum;
outputBuffer += std::to_string(sourceNum);
}
}
if (parseContext.lineDirectiveShouldSetNextLine()) {
@ -1016,33 +1022,36 @@ struct DoPreprocessing {
// directive. So the new line number for the current line is
newLineNum -= 1;
}
outputStream << std::endl;
outputBuffer += '\n';
// And we are at the next line of the #line directive now.
lineSync.setLineNum(newLineNum + 1);
});
parseContext.setVersionCallback(
[&lineSync, &outputStream](int line, int version, const char* str) {
[&lineSync, &outputBuffer](int line, int version, const char* str) {
lineSync.syncToLine(line);
outputStream << "#version " << version;
outputBuffer += "#version ";
outputBuffer += std::to_string(version);
if (str) {
outputStream << " " << str;
outputBuffer += ' ';
outputBuffer += str;
}
});
parseContext.setPragmaCallback([&lineSync, &outputStream](
parseContext.setPragmaCallback([&lineSync, &outputBuffer](
int line, const glslang::TVector<glslang::TString>& ops) {
lineSync.syncToLine(line);
outputStream << "#pragma ";
outputBuffer += "#pragma ";
for(size_t i = 0; i < ops.size(); ++i) {
outputStream << ops[i];
outputBuffer += ops[i].c_str();
}
});
parseContext.setErrorCallback([&lineSync, &outputStream](
parseContext.setErrorCallback([&lineSync, &outputBuffer](
int line, const char* errorMessage) {
lineSync.syncToLine(line);
outputStream << "#error " << errorMessage;
outputBuffer += "#error ";
outputBuffer += errorMessage;
});
int lastToken = EndOfInput; // lastToken records the last token processed.
@ -1058,7 +1067,7 @@ struct DoPreprocessing {
// Don't emit whitespace onto empty lines.
// Copy any whitespace characters at the start of a line
// from the input to the output.
outputStream << std::string(ppToken.loc.column - 1, ' ');
outputBuffer += std::string(ppToken.loc.column - 1, ' ');
}
// Output a space in between tokens, but not at the start of a line,
@ -1068,13 +1077,13 @@ struct DoPreprocessing {
(unNeededSpaceTokens.find((char)token) == std::string::npos) &&
(unNeededSpaceTokens.find((char)lastToken) == std::string::npos) &&
(noSpaceBeforeTokens.find((char)token) == std::string::npos)) {
outputStream << " ";
outputBuffer += ' ';
}
lastToken = token;
outputStream << ppToken.name;
outputBuffer += ppToken.name;
} while (true);
outputStream << std::endl;
*outputString = outputStream.str();
outputBuffer += '\n';
*outputString = std::move(outputBuffer);
bool success = true;
if (parseContext.getNumErrors() > 0) {