pipstransfo.tex

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  11 \title{PIPS - List of code transformations}
  12
  13
  14
  15 \begin{document}
  16
  17
  18 \chapter{List of Pips transformations}
  19
  20 \section{Memory allocation alteration}
  21
  22 \section{Loop transformations}
  23
  24 \section{Inter-procedural transformations}
  25
  26 \section{Base blocs transformations}
  27
  28 \section{Dead code removal}
  29
  30
  31
  32
  33 \begin{description}
  34 \item[loop unrolling]{
  35   is a loop transformation. Unrolling a loop by a factor of $n$ consists in the substitution of a loop
  36   body by itself, replicated $n$ times. A prelude and/or postlude are
  37   added to preserve the number of iteration.}
  38
  39 \item[inlining]{
  40   is a function transformation. Inlining a function
  41   \texttt{foo} in its caller \texttt{bar} consists in the substitution
  42   of the calls to \texttt{foo} in \texttt{bar} by the function body
  43   after replacement of the formal parameters by their effective
  44   parameters.
  45 }
  46
  47 \item[forward substitution]{
  48   is the process of replacing a reference read in an
  49   expression by the latest expression affected to it.}
  50
  51 \item[loop fusion]{
  52   is a loop transformation that replaces two loops by a single loops whose
  53   body is the concatenation of the bodies of the two initial loops.}
  54
  55 \item[loop tiling]{
  56   is a loop nest transformation that changes the loop execution order
  57   through a partitions of the iteration space into
  58   chunks, so that the iteration is performed over each chunk and in the
  59   chunks.}
  60
  61 \item[reduction detection]{
  62   is an analysis that identifies statements that perform a reduction over a
  63   variable.}
  64
  65 \item[parallelism detection]{
  66   is a common name for analysis that detect if a loop can be run in parallel.}
  67
  68 \item[parallelism extraction]{
  69   is a common name for code transformations that modifies loop nest to make it legal to
  70   run them in parallel.}
  71
  72 \item[directive generation]{
  73   is a common name for code transformations that annotate the code with directives.}
  74
  75 \item[constant propagation]{
  76   is a pass that replaces a variable by its value when this value is
  77   known at compile time.}
  78
  79 \item[instruction selection]{
  80   is the process of mapping parts of the IR to machine instructions.}
  81
  82 \item[goto elimination]{
  83   is the process of replacing \texttt{goto} instructions by a hierarchical control flow
  84   graph.}
  85 \item[outlining]{
  86   is the process of extracting part of a function body into a new function
  87   and replacing it in the initial function by a function call.}
  88
  89 \item[common subexpression elimination]{
  90   is the process of replacing similar expressions by a variable that holds
  91   the result of their evaluation.}
  92
  93 \item[loop interchange]{is a loop transformation that permutes two
  94   loops from a loop nest.}
  95
  96 \item[loop unswitching]{is a loop transformation that replaces a
  97   loop containing a test independent from the loop execution by a test
  98   containing the loop without the test in both true and false branch.}
  99
 100 \item[statement isolation]{is the process of replacing all
 101   variables referenced in a statement by newly declared variables. A
 102   prologue
 103   and an epilogue are added to copy old variable values to new variable, back
 104   and forth.}
 105
 106 \item[dead code elimination]{is the process of pruning from a
 107   function all the statements whose results are
 108   never used.}
 109
 110 \item[array linearization]{is the process of converting
 111   multidimensional array into unidimensional arrays, possibly with a
 112   conversion from array to pointer.}
 113
 114 \item[privatization]{is the process of  detecting variables that
 115   are private to a loop body, i.e.\ written first, then read.}
 116
 117 \item[loop normalization]{is a loop transformation that changes
 118   the loop initial increment value or the loop range to enforce certain values, generally
 119   1.}
 120
 121 \item[iteration clamping]{is a loop transformation that extends
 122   the loop range but guards the loop body with the former range.}
 123
 124 \item[flatten code]{is the process of pruning a function body from
 125   declaration blocks so that all declarations are made at the top level.}
 126
 127 \item[strength reduction]{is the process of replacing an operation
 128   by an operation of lower cost.}
 129
 130 \item[split update operator]{is the process of replacing an update
 131   operator by its expanded form.}
 132
 133 \item[n address code generation]{is the process of splitting
 134   complex expression in simpler ones that take at most $n$ operands.}
 135
 136 \item[memory footprint reduction]{is the process of tiling a loop
 137   to make sure the iteration over the tile has a memory footprint bounded by
 138   a given value.}
 139
 140 \item[redundant load-store elimination]{is an inter procedural transformation
 141   that optimizes data transfers by delaying and merging them.}
 142
 143 \item[invariant code motion]{is a loop transformation that moves outside
 144   of the loop
 145   the code from its body that is independent from the iteration.}
 146
 147
 148
 149 \item[loop rerolling]{finds manually unrolled loop and replace
 150   them by their non-unrolled version.}
 151 \end{description}
 152
 153 \end{document}