From dee1f2750b544dc2dd109231d5f8347beb142b8d Mon Sep 17 00:00:00 2001
From: Todd Neal <todd@tneal.org>
Date: Mon, 10 Aug 2015 21:05:35 -0500
Subject: [PATCH] [dev.ssa] cmd/compile/ssa: eliminate Zero with dse

Consider OpZero to be a store so it can be eliminated by dse.

Change-Id: Idebb6a190657b76966f0c5b20f2ec9f52fe47499
Reviewed-on: https://go-review.googlesource.com/13447
Reviewed-by: Keith Randall <khr@golang.org>
---
 src/cmd/compile/internal/ssa/deadstore.go     | 20 +++++++++++++++----
 .../compile/internal/ssa/deadstore_test.go    | 18 +++++++++++------
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/src/cmd/compile/internal/ssa/deadstore.go b/src/cmd/compile/internal/ssa/deadstore.go
index db3808639a..982bd7fa70 100644
--- a/src/cmd/compile/internal/ssa/deadstore.go
+++ b/src/cmd/compile/internal/ssa/deadstore.go
@@ -30,7 +30,7 @@ func dse(f *Func) {
 				for _, a := range v.Args {
 					if a.Block == b && a.Type.IsMemory() {
 						storeUse.add(a.ID)
-						if v.Op != OpStore {
+						if v.Op != OpStore && v.Op != OpZero {
 							// CALL, DUFFCOPY, etc. are both
 							// reads and writes.
 							loadUse.add(a.ID)
@@ -77,12 +77,24 @@ func dse(f *Func) {
 			// Clear all shadowed addresses.
 			shadowed.clear()
 		}
-		if v.Op == OpStore {
+		if v.Op == OpStore || v.Op == OpZero {
 			if shadowed.contains(v.Args[0].ID) {
 				// Modify store into a copy
-				v.Op = OpCopy
+				if v.Op == OpStore {
+					// store addr value mem
+					v.SetArgs1(v.Args[2])
+				} else {
+					// zero addr mem
+					sz := v.Args[0].Type.Elem().Size()
+					if v.AuxInt != sz {
+						f.Fatalf("mismatched zero/store sizes: %d and %d [%s]",
+							v.AuxInt, sz, v.LongString())
+					}
+					v.SetArgs1(v.Args[1])
+				}
 				v.Aux = nil
-				v.SetArgs1(v.Args[2])
+				v.AuxInt = 0
+				v.Op = OpCopy
 			} else {
 				shadowed.add(v.Args[0].ID)
 			}
diff --git a/src/cmd/compile/internal/ssa/deadstore_test.go b/src/cmd/compile/internal/ssa/deadstore_test.go
index 8c0a875cad..8d9b4b1298 100644
--- a/src/cmd/compile/internal/ssa/deadstore_test.go
+++ b/src/cmd/compile/internal/ssa/deadstore_test.go
@@ -4,9 +4,7 @@
 
 package ssa
 
-import (
-	"testing"
-)
+import "testing"
 
 func TestDeadStore(t *testing.T) {
 	c := testConfig(t)
@@ -18,9 +16,12 @@ func TestDeadStore(t *testing.T) {
 			Valu("v", OpConstBool, TypeBool, 0, true),
 			Valu("addr1", OpAddr, ptrType, 0, nil, "sb"),
 			Valu("addr2", OpAddr, ptrType, 0, nil, "sb"),
-			Valu("store1", OpStore, TypeMem, 0, nil, "addr1", "v", "start"),
+			Valu("addr3", OpAddr, ptrType, 0, nil, "sb"),
+			Valu("zero1", OpZero, TypeMem, 8, nil, "addr3", "start"),
+			Valu("store1", OpStore, TypeMem, 0, nil, "addr1", "v", "zero1"),
 			Valu("store2", OpStore, TypeMem, 0, nil, "addr2", "v", "store1"),
 			Valu("store3", OpStore, TypeMem, 0, nil, "addr1", "v", "store2"),
+			Valu("store4", OpStore, TypeMem, 0, nil, "addr3", "v", "store3"),
 			Goto("exit")),
 		Bloc("exit",
 			Exit("store3")))
@@ -29,10 +30,15 @@ func TestDeadStore(t *testing.T) {
 	dse(fun.f)
 	CheckFunc(fun.f)
 
-	v := fun.values["store1"]
-	if v.Op != OpCopy {
+	v1 := fun.values["store1"]
+	if v1.Op != OpCopy {
 		t.Errorf("dead store not removed")
 	}
+
+	v2 := fun.values["zero1"]
+	if v2.Op != OpCopy {
+		t.Errorf("dead store (zero) not removed")
+	}
 }
 func TestDeadStorePhi(t *testing.T) {
 	// make sure we don't get into an infinite loop with phi values.
-- 
2.48.1