Camil Demetrescu edited osr-llvm.tex  over 8 years ago

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%\subsection{Example}  In this section we discuss how to implement the OSR approach of \mysection\ref{se:overview} in LLVM. Our discussion is based on a simple example that illustrates a profile-driven optimization scenario. We start from a simple base function ({\tt isord}) that checks whether an array of numbers is ordered according to some criterion specified by a comparator, as shown in \myfigure\ref{fi:isord-example}. Our goal is to instrument {\tt isort} so that, whenever the number of iterations of {\tt isord} exceeds a certain threshold, control is dynamically diverted to a faster version generated on the fly by inlining the comparator.   The IR code shown in this section has been generated with \clang\ and instrumented with \osrkit, an LLVM-based a  library we prototyped to help VM builders implement OSR in LLVM\footnote{Virtual register names and labels in the LLVM-produced IR code shown in this paper have been refactored to make the code more readable.}. %To explain how the OSR approach of \mysection\ref{se:overview} can be implemented in LLVM, we consider the simple example of \myfigure\ref{fi:isord-example}. Function {\tt isord} checks whether an array of numbers is ordered according to some criterion specified by a comparator.