From 97a268624c9f2830133d2bdfae677f5d99ec82cb Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Fri, 24 Jan 2020 13:52:41 -0800
Subject: [PATCH] cmd/compile: add -d=ssa/check/seed=SEED

This change adds the option to run the ssa checker with a random seed.
The current system uses a completely fixed seed,
which is good for reproducibility but bad for exploring the state space.

Preserve what we have, but also provide a way for the caller
to provide a seed. The caller can report the seed
alongside any failures.

Change-Id: I2676a8112d8260e6cac86d95d2e8db4d3221aeeb
Reviewed-on: https://go-review.googlesource.com/c/go/+/216418
Reviewed-by: Keith Randall <khr@golang.org>
---
 src/cmd/compile/internal/ssa/compile.go | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/cmd/compile/internal/ssa/compile.go b/src/cmd/compile/internal/ssa/compile.go
index 8551c0a54b..448b1cf814 100644
--- a/src/cmd/compile/internal/ssa/compile.go
+++ b/src/cmd/compile/internal/ssa/compile.go
@@ -35,7 +35,8 @@ func Compile(f *Func) {
 
 	var rnd *rand.Rand
 	if checkEnabled {
-		rnd = rand.New(rand.NewSource(int64(crc32.ChecksumIEEE(([]byte)(f.Name)))))
+		seed := int64(crc32.ChecksumIEEE(([]byte)(f.Name))) ^ int64(checkRandSeed)
+		rnd = rand.New(rand.NewSource(seed))
 	}
 
 	// hook to print function & phase if panic happens
@@ -199,7 +200,10 @@ func (p *pass) addDump(s string) {
 }
 
 // Run consistency checker between each phase
-var checkEnabled = false
+var (
+	checkEnabled  = false
+	checkRandSeed = 0
+)
 
 // Debug output
 var IntrinsicsDebug int
@@ -253,7 +257,7 @@ where:
 ` + phasenames + `
 
 - <flag> is one of:
-    on, off, debug, mem, time, test, stats, dump
+    on, off, debug, mem, time, test, stats, dump, seed
 
 - <value> defaults to 1
 
@@ -271,6 +275,10 @@ Examples:
     -d=ssa/check/on
 enables checking after each phase
 
+	-d=ssa/check/seed=1234
+enables checking after each phase, using 1234 to seed the PRNG
+used for value order randomization
+
     -d=ssa/all/time
 enables time reporting for all phases
 
@@ -294,6 +302,12 @@ commas. For example:
 		debugPoset = checkEnabled
 		return ""
 	}
+	if phase == "check" && flag == "seed" {
+		checkEnabled = true
+		checkRandSeed = val
+		debugPoset = checkEnabled
+		return ""
+	}
 
 	alltime := false
 	allmem := false
-- 
2.50.0