cmd/compile/internal/gc: avoid potential endless loop in float printing

The compiler should not usually call Fconv with an infinity, but if
it does, Fconv will end in an endless loop. Test for infinities early.

Change-Id: I48f366466538b0bd26a851e01258725025babaff
Reviewed-on: https://go-review.googlesource.com/16777
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/cmd/compile/internal/gc/mparith3.go b/src/cmd/compile/internal/gc/mparith3.go
index 4aa283fe33aa2c806c056e6f78565e963e29d16e..889c461cc9e44114ed8a8893aaeb9809997de195 100644 (file)
--- a/src/cmd/compile/internal/gc/mparith3.go
+++ b/src/cmd/compile/internal/gc/mparith3.go
@@ -207,6 +207,11 @@ func Fconv(fvp *Mpflt, flag int) string {
                sign = "+"
        }
 
+       // Don't try to convert infinities (will not terminate).
+       if f.IsInf() {
+               return sign + "Inf"
+       }
+
        // Use fmt formatting if in float64 range (common case).
        if x, _ := f.Float64(); !math.IsInf(x, 0) {
                return fmt.Sprintf("%s%.6g", sign, x)