cmd/compile: remove 68857 ModU flowLimit workaround in prove

We can know this is correct because all the testcases added by CL 605156 are still passing.
Partial revert of CL 605156 (everything but the testcases).

Change-Id: I5d8daadb4cb35a9de29daaabc22baee642511fe0
Reviewed-on: https://go-review.googlesource.com/c/go/+/714941
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go
index d448f6e7fc95d112a5a523018eb344dc96dc7c97..5010fa3a6d352997b381f5a21cf22ea771243683 100644 (file)
--- a/src/cmd/compile/internal/ssa/prove.go
+++ b/src/cmd/compile/internal/ssa/prove.go
@@ -1962,19 +1962,6 @@ func (ft *factsTable) flowLimit(v *Value) bool {
                b := ft.limits[v.Args[1].ID]
                bitsize := uint(v.Type.Size()) * 8
                return ft.newLimit(v, a.mul(b.exp2(bitsize), bitsize))
-       case OpMod64, OpMod32, OpMod16, OpMod8:
-               a := ft.limits[v.Args[0].ID]
-               b := ft.limits[v.Args[1].ID]
-               if !(a.nonnegative() && b.nonnegative()) {
-                       // TODO: we could handle signed limits but I didn't bother.
-                       break
-               }
-               fallthrough
-       case OpMod64u, OpMod32u, OpMod16u, OpMod8u:
-               a := ft.limits[v.Args[0].ID]
-               b := ft.limits[v.Args[1].ID]
-               // Underflow in the arithmetic below is ok, it gives to MaxUint64 which does nothing to the limit.
-               return ft.unsignedMax(v, min(a.umax, b.umax-1))
        case OpDiv64, OpDiv32, OpDiv16, OpDiv8:
                a := ft.limits[v.Args[0].ID]
                b := ft.limits[v.Args[1].ID]
@@ -2484,6 +2471,14 @@ func addLocalFacts(ft *factsTable, b *Block) {
                        OpRsh32Ux64, OpRsh32Ux32, OpRsh32Ux16, OpRsh32Ux8,
                        OpRsh64Ux64, OpRsh64Ux32, OpRsh64Ux16, OpRsh64Ux8:
                        ft.update(b, v, v.Args[0], unsigned, lt|eq)
+               case OpMod64, OpMod32, OpMod16, OpMod8:
+                       a := ft.limits[v.Args[0].ID]
+                       b := ft.limits[v.Args[1].ID]
+                       if !(a.nonnegative() && b.nonnegative()) {
+                               // TODO: we could handle signed limits but I didn't bother.
+                               break
+                       }
+                       fallthrough
                case OpMod64u, OpMod32u, OpMod16u, OpMod8u:
                        ft.update(b, v, v.Args[0], unsigned, lt|eq)
                        // Note: we have to be careful that this doesn't imply