From 251199c430929d072cbe4cc8dc97659fa3d1ce6a Mon Sep 17 00:00:00 2001
From: Nigel Tao <nigeltao@golang.org>
Date: Thu, 23 Aug 2012 16:17:22 +1000
Subject: [PATCH] cmd/8g: roll back the small integer constant optimizations
 introduced in 13416:67c0b8c8fb29 "faster code, mainly for rotate" [1]. The
 codegen can run out of registers if there are too many small-int arithmetic
 ops.

An alternative approach is to copy 6g's sbop/abop codegen to 8g, but
this change is less risky.

Fixes #3835.

[1] http://code.google.com/p/go/source/diff?spec=svn67c0b8c8fb29b1b7b6221977af6b89cae787b941&name=67c0b8c8fb29&r=67c0b8c8fb29b1b7b6221977af6b89cae787b941&format=side&path=/src/cmd/8g/cgen.c

R=rsc, remyoudompheng, r
CC=golang-dev
https://golang.org/cl/6450163
---
 src/cmd/8g/cgen.c        |  8 +-------
 test/fixedbugs/bug451.go | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 7 deletions(-)
 create mode 100644 test/fixedbugs/bug451.go

diff --git a/src/cmd/8g/cgen.c b/src/cmd/8g/cgen.c
index aefa15a670..1ae49acaa0 100644
--- a/src/cmd/8g/cgen.c
+++ b/src/cmd/8g/cgen.c
@@ -392,13 +392,7 @@ sbop:	// symmetric binary
 	}
 
 abop:	// asymmetric binary
-	if(smallintconst(nr)) {
-		regalloc(&n1, nr->type, res);
-		cgen(nl, &n1);
-		gins(a, nr, &n1);
-		gmove(&n1, res);
-		regfree(&n1);
-	} else if(nl->ullman >= nr->ullman) {
+	if(nl->ullman >= nr->ullman) {
 		tempname(&nt, nl->type);
 		cgen(nl, &nt);
 		mgen(nr, &n2, N);
diff --git a/test/fixedbugs/bug451.go b/test/fixedbugs/bug451.go
new file mode 100644
index 0000000000..d2e4a0b44a
--- /dev/null
+++ b/test/fixedbugs/bug451.go
@@ -0,0 +1,38 @@
+// run
+
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 3835: 8g tries to optimize arithmetic involving integer
+// constants, but can run out of registers in the process.
+
+package main
+
+var a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z, A, B, C, D, E, F, G int
+
+func foo() int {
+	return a + 1 + b + 2 + c + 3 + d + 4 + e + 5 + f + 6 + g + 7 + h + 8 + i + 9 + j + 10 +
+		k + 1 + l + 2 + m + 3 + n + 4 + o + 5 + p + 6 + q + 7 + r + 8 + s + 9 + t + 10 +
+		u + 1 + v + 2 + w + 3 + x + 4 + y + 5 + z + 6 + A + 7 + B + 8 + C + 9 + D + 10 +
+		E + 1 + F + 2 + G + 3
+}
+
+func bar() int8 {
+	var (
+		W int16
+		X int32
+		Y int32
+		Z int32
+	)
+	return int8(W+int16(X+3)+3) * int8(Y+3+Z*3)
+}
+
+func main() {
+	if foo() == 0 {
+		panic("foo")
+	}
+	if bar() == 0 {
+		panic("bar")
+	}
+}
-- 
2.48.1