cmd/gc: avoid confusing error message "ovf in mpaddxx"

Fixes #6889

LGTM=rsc
R=gri, rsc
CC=golang-codereviews
https://golang.org/cl/85080044

diff --git a/src/cmd/gc/mparith2.c b/src/cmd/gc/mparith2.c
index 9b2f664f7b7a9be487710cebc41442493b699947..5cf98c62c634cdfd91ae3328a69f57c662b3452c 100644 (file)
--- a/src/cmd/gc/mparith2.c
+++ b/src/cmd/gc/mparith2.c
@@ -300,13 +300,21 @@ mpmulfixfix(Mpint *a, Mpint *b)
        for(i=0; i<na; i++) {
                x = *a1++;
                for(j=0; j<Mpscale; j++) {
-                       if(x & 1)
+                       if(x & 1) {
+                               if(s.ovf) {
+                                       q.ovf = 1;
+                                       goto out;
+                               }
                                mpaddfixfix(&q, &s, 1);
+                               if(q.ovf)
+                                       goto out;
+                       }
                        mplsh(&s, 1);
                        x >>= 1;
                }
        }
 
+out:
        q.neg = a->neg ^ b->neg;
        mpmovefixfix(a, &q);
        if(a->ovf)

diff --git a/test/fixedbugs/issue6889.go b/test/fixedbugs/issue6889.go
new file mode 100644 (file)
index 0000000..46bb5da
--- /dev/null
+++ b/test/fixedbugs/issue6889.go
@@ -0,0 +1,103 @@
+// errorcheck
+
+// Copyright 2014 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 6889: confusing error message: ovf in mpaddxx
+
+package main
+
+const (
+       f1  = 1
+       f2  = f1 * 2
+       f3  = f2 * 3
+       f4  = f3 * 4
+       f5  = f4 * 5
+       f6  = f5 * 6
+       f7  = f6 * 7
+       f8  = f7 * 8
+       f9  = f8 * 9
+       f10 = f9 * 10
+       f11 = f10 * 11
+       f12 = f11 * 12
+       f13 = f12 * 13
+       f14 = f13 * 14
+       f15 = f14 * 15
+       f16 = f15 * 16
+       f17 = f16 * 17
+       f18 = f17 * 18
+       f19 = f18 * 19
+       f20 = f19 * 20
+       f21 = f20 * 21
+       f22 = f21 * 22
+       f23 = f22 * 23
+       f24 = f23 * 24
+       f25 = f24 * 25
+       f26 = f25 * 26
+       f27 = f26 * 27
+       f28 = f27 * 28
+       f29 = f28 * 29
+       f30 = f29 * 30
+       f31 = f30 * 31
+       f32 = f31 * 32
+       f33 = f32 * 33
+       f34 = f33 * 34
+       f35 = f34 * 35
+       f36 = f35 * 36
+       f37 = f36 * 37
+       f38 = f37 * 38
+       f39 = f38 * 39
+       f40 = f39 * 40
+       f41 = f40 * 41
+       f42 = f41 * 42
+       f43 = f42 * 43
+       f44 = f43 * 44
+       f45 = f44 * 45
+       f46 = f45 * 46
+       f47 = f46 * 47
+       f48 = f47 * 48
+       f49 = f48 * 49
+       f50 = f49 * 50
+       f51 = f50 * 51
+       f52 = f51 * 52
+       f53 = f52 * 53
+       f54 = f53 * 54
+       f55 = f54 * 55
+       f56 = f55 * 56
+       f57 = f56 * 57
+       f58 = f57 * 58
+       f59 = f58 * 59
+       f60 = f59 * 60
+       f61 = f60 * 61
+       f62 = f61 * 62
+       f63 = f62 * 63
+       f64 = f63 * 64
+       f65 = f64 * 65
+       f66 = f65 * 66
+       f67 = f66 * 67
+       f68 = f67 * 68
+       f69 = f68 * 69
+       f70 = f69 * 70
+       f71 = f70 * 71
+       f72 = f71 * 72
+       f73 = f72 * 73
+       f74 = f73 * 74
+       f75 = f74 * 75
+       f76 = f75 * 76
+       f77 = f76 * 77
+       f78 = f77 * 78
+       f79 = f78 * 79
+       f80 = f79 * 80
+       f81 = f80 * 81
+       f82 = f81 * 82
+       f83 = f82 * 83
+       f84 = f83 * 84
+       f85 = f84 * 85
+       f86 = f85 * 86
+       f87 = f86 * 87
+       f88 = f87 * 88
+       f89 = f88 * 89
+       f90 = f89 * 90
+       f91 = f90 * 91 // ERROR "overflow"
+)