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perf metric: Avoid events for an 'if' constant result

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For a metric like:

  CONST if expr else CONST

if the values of CONST are identical then expr doesn't need evaluating,
and events, in order to compute a result.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: John Garry <john.garry@huawei.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandeep Dasgupta <sdasgup@google.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20210923074616.674826-14-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Ian Rogers
2021-09-23 00:46:16 -07:00
committed by Arnaldo Carvalho de Melo
parent a8e4e88083
commit 94886961e3
2 changed files with 17 additions and 0 deletions
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10
tools/perf/util/expr.y
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@@ -142,6 +142,16 @@ if_expr: expr IF expr ELSE expr
$$.ids = $1.ids;
ids__free($3.ids);
ids__free($5.ids);
} else if ($1.val == $5.val) {
/*
* LHS == RHS, so both are an identical constant. No need to
* evaluate any events.
*/
$$.val = $1.val;
$$.ids = NULL;
ids__free($1.ids);
ids__free($3.ids);
ids__free($5.ids);
} else {
/*
* Value is either the LHS or RHS and we need the IF expression