7.12.3 Slicing

Once a slice has been generated it can be viewed in various ways using the mslice tool. The output of the mslice tool will look something like the following:

Procedure            Path/Port File:Line Count (1)
pred mrg.merge/3-0   CALL      mrg.m:60     14 (1)
pred mrg.merge/3-0   EXIT      mrg.m:60     14 (1)
pred mrg.msort_n/4-0 CALL      mrg.m:33     12 (1)
pred mrg.msort_n/4-0 EXIT      mrg.m:33     12 (1)
pred mrg.msort_n/4-0 <?;>      mrg.m:35     12 (1)

Each row corresponds to a label in the program. The meanings of the columns are as follows:

• ‘Procedure’: This column displays the procedure that the label relates to.
• ‘Path/Port’: For interface events this column displays the event port, while for internal events it displays the goal path. (See Tracing of Mercury programs for an explanation of interface and internal events.)
• ‘File:Line’: This column displays the context of the event.
• ‘Count’: This column displays how many times the event was executed. The number in parentheses for each event row says in how many runs the event was executed. The number in parentheses in the heading row (after the word "Count") indicates how many runs were represented in the trace counts file analysed by the mslice tool.

The mslice tool is invoked using a command of the form:

mslice [-s sortspec] [-l N] [-m module] [-n N] [-p N] [-f N] file

where ‘file’ is a trace count file, generated either directly by a program run or indirectly by the ‘mtc_union’ or ‘mtc_diff’ tools.

The ‘-s’ or ‘--sort’ option specifies how the output should be sorted. ‘sortspec’ should be a string made up of any combination of the letters ‘cCtT’. Each letter specifies a column and direction to sort on:

• ‘c’: Count ascending
• ‘C’: Count descending
• ‘t’: Number of runs ascending
• ‘T’: Number of runs descending

For example, the option ‘-s cT’ will sort the output table by the Count column in ascending order. If the counts for two or more events are the same, then those events will be sorted by number of runs in descending order.

The default is to sort descending on the Count column.

The ‘-l’ or ‘--limit’ option limits the output to ‘N’ lines.

The ‘-m’ or ‘--module’ option limits the output to events only from the given module.

The ‘-n’ or ‘--max-name-column’ option’s argument gives the maximum width of the column containing predicate names. If the argument is zero, there is no maximum width.

The ‘-p’ or ‘--max-path-column’ option’s argument gives the maximum width of the column containing ports and goal paths. If the argument is zero, there is no maximum width.

The ‘-f’ or ‘--max-file-column’ option’s argument gives the maximum width of the column containing file names and line numbers. If the argument is zero, there is no maximum width.