pipstransfo.tex

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  12 \title{PIPS~--- List of code transformations}
  13
  14
  15
  16 \begin{document}
  17
  18
  19 \chapter{List of Pips transformations}
  20
  21 \section{Memory allocation alteration}
  22
  23 \begin{description}
  24
  25 \item[scalar renaming]{is the process of renaming scalar variables to
  26     suppress false data dependencies.}
  27
  28 \item[privatization]{is the process of detecting variables that are
  29     private to a loop body, i.e.\ written first, then read.}
  30
  31 \end{description}
  32
  33
  34 \section{Loop transformations}
  35
  36 \begin{description}
  37
  38 \item[loop unrolling]{
  39   is a loop transformation.
  40   Unrolling a loop by a factor of $n$ consists in the substitution of a loop
  41   body by itself, replicated $n$ times. A prelude and/or postlude are
  42   added to preserve the number of iteration.}
  43
  44 \item[loop fusion]{
  45   is a loop transformation that replaces two loops by a single loops whose
  46   body is the concatenation of the bodies of the two initial loops.}
  47
  48 \item[loop tiling]{
  49   is a loop nest transformation that changes the loop execution order
  50   through a partitions of the iteration space into
  51   chunks, so that the iteration is performed over each chunk and in the
  52   chunks.}
  53
  54 \item[loop interchange]{is a loop transformation that permutes two
  55   loops from a loop nest.}
  56
  57 \item[loop unswitching]{is a loop transformation that replaces a
  58   loop containing a test independent from the loop execution by a test
  59   containing the loop without the test in both true and false branch.}
  60
  61 \item[loop normalization]{is a loop transformation that changes
  62   the loop initial increment value or the loop range to enforce certain values,
  63   generally~1.}
  64
  65 \end{description}
  66
  67 \section{Inter-procedural transformations}
  68
  69 \section{Base blocs transformations}
  70
  71 \section{Dead code removal}
  72
  73
  74
  75
  76 \begin{description}
  77
  78
  79 \item[inlining]{
  80   is a function transformation. Inlining a function
  81   \texttt{foo} in its caller \texttt{bar} consists in the substitution
  82   of the calls to \texttt{foo} in \texttt{bar} by the function body
  83   after replacement of the formal parameters by their effective
  84   parameters.
  85 }
  86
  87 \item[forward substitution]{
  88   is the process of replacing a reference read in an
  89   expression by the latest expression affected to it.}
  90
  91
  92
  93
  94
  95 \item[reduction detection]{
  96   is an analysis that identifies statements that perform a reduction over a
  97   variable.}
  98
  99 \item[parallelism detection]{
 100   is a common name for analysis that detect if a loop can be run in parallel.}
 101
 102 \item[parallelism extraction]{
 103   is a common name for code transformations that modifies loop nest to make it legal to
 104   run them in parallel.}
 105
 106 \item[directive generation]{
 107   is a common name for code transformations that annotate the code with directives.}
 108
 109 \item[constant propagation]{
 110   is a pass that replaces a variable by its value when this value is
 111   known at compile time.}
 112
 113 \item[instruction selection]{
 114   is the process of mapping parts of the IR to machine instructions.}
 115
 116 \item[goto elimination]{
 117   is the process of replacing \texttt{goto} instructions by a hierarchical control flow
 118   graph.}
 119 \item[outlining]{
 120   is the process of extracting part of a function body into a new function
 121   and replacing it in the initial function by a function call.}
 122
 123 \item[common subexpression elimination]{
 124   is the process of replacing similar expressions by a variable that holds
 125   the result of their evaluation.}
 126
 127
 128
 129 \item[statement isolation]{is the process of replacing all
 130   variables referenced in a statement by newly declared variables. A
 131   prologue
 132   and an epilogue are added to copy old variable values to new variable, back
 133   and forth.}
 134
 135 \item[dead code elimination]{is the process of pruning from a
 136   function all the statements whose results are
 137   never used.}
 138
 139 \item[array linearization]{is the process of converting
 140   multidimensional array into unidimensional arrays, possibly with a
 141   conversion from array to pointer.}
 142
 143 \item[loop normalization]{is a loop transformation that changes
 144   the loop initial increment value or the loop range to enforce certain values, generally~1.}
 145
 146 \item[iteration clamping]{is a loop transformation that extends
 147   the loop range but guards the loop body with the former range.}
 148
 149 \item[flatten code]{is the process of pruning a function body from
 150   declaration blocks so that all declarations are made at the top level.}
 151
 152 \item[strength reduction]{is the process of replacing an operation
 153   by an operation of lower cost.}
 154
 155 \item[split update operator]{is the process of replacing an update
 156   operator by its expanded form.}
 157
 158 \item[n address code generation]{is the process of splitting
 159   complex expression in simpler ones that take at most $n$ operands.}
 160
 161 \item[memory footprint reduction]{is the process of tiling a loop
 162   to make sure the iteration over the tile has a memory footprint bounded by
 163   a given value.}
 164
 165 \item[redundant load-store elimination]{is an inter procedural transformation
 166   that optimizes data transfers by delaying and merging them.}
 167
 168 \item[invariant code motion]{is a loop transformation that moves outside
 169   of the loop
 170   the code from its body that is independent from the iteration.}
 171
 172
 173
 174 \item[loop rerolling]{finds manually unrolled loop and replace
 175   them by their non-unrolled version.}
 176 \end{description}
 177
 178
 179 \section{References}
 180
 181
 182 \end{document}