commit 07749aef988e55aba0c67aeb3607f42b58d4e249
author Robert Griesemer <gri@golang.org> Mon Mar 21 10:52:03 2016 -0700
committer Robert Griesemer <gri@golang.org> Mon Mar 21 17:58:21 2016 +0000
tree bc2fa6adcf9dd83453e02902a15a572d9bac962e
parent d3253876f20ea39dbd7694ecaa5022e6cc147ccc

cmd/compile: special-case const comparisons against zero

Constant comparisons against 0 are reasonably common.
Special-case and avoid allocating a new zero value each time.

Change-Id: I6c526c8ab30ef7f0fef59110133c764b7b90ba05
Reviewed-on: https://go-review.googlesource.com/20956
Reviewed-by: Alan Donovan <adonovan@google.com>

src/cmd/compile/internal/gc/walk.go

diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 428d309..7a82a80 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -10,8 +10,6 @@
 	"strings"
 )
 
-var mpzero Mpint
-
 // The constant is known to runtime.
 const (
 	tmpstringbufsize = 32
@@ -1229,7 +1227,7 @@
 		}
 
 		if Isconst(n.Right, CTINT) {
-			if n.Right.Val().U.(*Mpint).Cmp(&mpzero) < 0 || n.Right.Val().U.(*Mpint).Cmp(Maxintval[TINT]) > 0 {
+			if n.Right.Val().U.(*Mpint).CmpInt64(0) < 0 || n.Right.Val().U.(*Mpint).Cmp(Maxintval[TINT]) > 0 {
 				Yyerror("index out of bounds")
 			}
 		}