Changes between Version 29 and Version 30 of PIRCDevelopment

Timestamp:

08/09/09 12:35:40 (12 years ago)

Author:

kjs

Comment:

--

PIRCDevelopment

@@ -374 +374 @@
 The implementation can be found in [source:/trunk/compilers/pirc/src/pirregalloc.c]. Whether or not to use the register optimizer depends on how your program is used. If you have a large program that you will run many times, and memory usage is important, then you should activate it. If, on the other hand, runtime performance (compilation time included) is important, you should not activate it, as it takes additional time to perform the register optimization. In order to activate the register optimizer, use the {{{-r}}} command line option when running PIRC.
 
-
+For each symbol (PIR register or declared symbol), a [source:/trunk/compilers/pirc/src/pirregalloc.h#L29 live_interval struct] instance is allocated. Most important are the {{{startpoint}}} and {{{endpoint}}} fields, which keep track of the start and end point respectively of the live interval of the variable. Consider the following example:
+
+{{{
+
+  .sub main
+0   $I10 = 1
+1   $I11 = 2
+2   print $I0
+3   print $I1
+  .end
+
+}}}
+
+In this code snippet, the numbers in front of the statements indicate the sequence of instructions. As you can see, {{{$I0}}} lives from 0 to 2, whereas {{{$I1}}} lives from 1 to 3. Since these live intervals are overlapping, this means that these variables cannot share a register. On the other hand, consider the following example:
+
+{{{
+
+   .sub main
+0    $I0 = 1
+1    print $I0
+2    $I1 = 2
+3    print $I1
+   .end
+
+}}}
+
+In this case, {{{$I0}}} lives from 0 to 1, whereas {{{$1}}} lives from 2 to 3. Since they do not overlap, these variables can share a register. This can be calculated by the algorithm described in the above mentioned paper. These details will not be discussed here; instead the reader is referred to the paper.
 
 == Bytecode Generation ==