cmd/compile: add countRule rewrite rule helper

noteRule is useful when you're trying to debug
a particular rule, or get a general sense for
how often a rule fires overall.

It is less useful if you're trying to figure
out which functions might be useful to benchmark
to ascertain the impact of a newly added rule.

Enter countRule. You use it like noteRule,
except that you get per-function summaries.

Sample output:

 # runtime
(*mspan).sweep: idx1=1
evacuate_faststr: idx1=1
evacuate_fast32: idx1=1
evacuate: idx1=2
evacuate_fast64: idx1=1
sweepone: idx1=1
purgecachedstats: idx1=1
mProf_Free: idx1=1

This suggests that the map benchmarks
might be good to run for this added rule.

Change-Id: Id471c3231f1736165f2020f6979ff01c29677808
Reviewed-on: https://go-review.googlesource.com/c/go/+/167088
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/src/cmd/compile/internal/ssa/func.go b/src/cmd/compile/internal/ssa/func.go
index 4f6dbff208..df8df64dd5 100644
--- a/src/cmd/compile/internal/ssa/func.go
+++ b/src/cmd/compile/internal/ssa/func.go
@@ -38,9 +38,10 @@ type Func struct {
 	// Given an environment variable used for debug hash match,
 	// what file (if any) receives the yes/no logging?
 	logfiles       map[string]writeSyncer
-	HTMLWriter     *HTMLWriter // html writer, for debugging
-	DebugTest      bool        // default true unless $GOSSAHASH != ""; as a debugging aid, make new code conditional on this and use GOSSAHASH to binary search for failing cases
-	PrintOrHtmlSSA bool        // true if GOSSAFUNC matches, true even if fe.Log() (spew phase results to stdout) is false.
+	HTMLWriter     *HTMLWriter    // html writer, for debugging
+	DebugTest      bool           // default true unless $GOSSAHASH != ""; as a debugging aid, make new code conditional on this and use GOSSAHASH to binary search for failing cases
+	PrintOrHtmlSSA bool           // true if GOSSAFUNC matches, true even if fe.Log() (spew phase results to stdout) is false.
+	ruleMatches    map[string]int // number of times countRule was called during compilation for any given string
 
 	scheduled bool // Values in Blocks are in final order
 	laidout   bool // Blocks are ordered