cmd/compile: use proved bounds to remove signed division fix-ups

prove is able to find 94 occurrences in std cmd where a divisor
can't have the value -1. The change removes
the extraneous fix-up code for these cases.

Fixes #25239

Change-Id: Ic184de971f47cc57c702eb72805b8e291c14035d
Reviewed-on: https://go-review.googlesource.com/c/130215
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ssa/rewrite.go

@@ -451,6 +451,16 @@ func extend32Fto64F(f float32) float64 {
 	return math.Float64frombits(r)
 }
 
+// NeedsFixUp reports whether the division needs fix-up code.
+func NeedsFixUp(v *Value) bool {
+	return v.AuxInt == 0
+}
+
+// i2f is used in rules for converting from an AuxInt to a float.
+func i2f(i int64) float64 {
+	return math.Float64frombits(uint64(i))
+}
+
 // auxFrom64F encodes a float64 value so it can be stored in an AuxInt.
 func auxFrom64F(f float64) int64 {
 	return int64(math.Float64bits(f))