1 files changed, 25 insertions, 11 deletions

diff --git a/src/cmd/compile/internal/ssa/loopbce.go b/src/cmd/compile/internal/ssa/loopbce.go
index fc96834b88..0d3130fe9a 100644
--- a/src/cmd/compile/internal/ssa/loopbce.go
+++ b/src/cmd/compile/internal/ssa/loopbce.go
@@ -235,9 +235,11 @@ nextblock:
 							if init.AuxInt > v {
 								return false
 							}
+							// TODO(1.27): investigate passing a smaller-magnitude overflow limit to addU
+							// for addWillOverflow.
 							v = addU(init.AuxInt, diff(v, init.AuxInt)/uint64(step)*uint64(step))
 						}
-						if addWillOverflow(v, step) {
+						if addWillOverflow(v, step, maxSignedValue(ind.Type)) {
 							return false
 						}
 						if inclusive && v != limit.AuxInt || !inclusive && v+1 != limit.AuxInt {
@@ -271,7 +273,7 @@ nextblock:
 					// for i := 0; i < KNN&^(k-1) ; i += k // k a power of 2
 					// for i := 0; i < KNN&(-k) ; i += k // k a power of 2
 				} else { // step < 0
-					if limit.Op == OpConst64 {
+					if limit.isGenericIntConst() {
 						// Figure out the actual smallest value.
 						v := limit.AuxInt
 						if !inclusive {
@@ -285,9 +287,11 @@ nextblock:
 							if init.AuxInt < v {
 								return false
 							}
+							// TODO(1.27): investigate passing a smaller-magnitude underflow limit to subU
+							// for subWillUnderflow.
 							v = subU(init.AuxInt, diff(init.AuxInt, v)/uint64(-step)*uint64(-step))
 						}
-						if subWillUnderflow(v, -step) {
+						if subWillUnderflow(v, -step, minSignedValue(ind.Type)) {
 							return false
 						}
 						if inclusive && v != limit.AuxInt || !inclusive && v-1 != limit.AuxInt {
@@ -347,14 +351,22 @@ nextblock:
 	return iv
 }
 
-// addWillOverflow reports whether x+y would result in a value more than maxint.
-func addWillOverflow(x, y int64) bool {
-	return x+y < x
+// subWillUnderflow checks if x - y underflows the min value.
+// y must be positive.
+func subWillUnderflow(x, y int64, min int64) bool {
+	if y < 0 {
+		base.Fatalf("expecting positive value")
+	}
+	return x < min+y
 }
 
-// subWillUnderflow reports whether x-y would result in a value less than minint.
-func subWillUnderflow(x, y int64) bool {
-	return x-y > x
+// addWillOverflow checks if x + y overflows the max value.
+// y must be positive.
+func addWillOverflow(x, y int64, max int64) bool {
+	if y < 0 {
+		base.Fatalf("expecting positive value")
+	}
+	return x > max-y
 }
 
 // diff returns x-y as a uint64. Requires x>=y.
@@ -375,7 +387,8 @@ func addU(x int64, y uint64) int64 {
 		x += 1
 		y -= 1 << 63
 	}
-	if addWillOverflow(x, int64(y)) {
+	// TODO(1.27): investigate passing a smaller-magnitude overflow limit in here.
+	if addWillOverflow(x, int64(y), maxSignedValue(types.Types[types.TINT64])) {
 		base.Fatalf("addU overflowed %d + %d", x, y)
 	}
 	return x + int64(y)
@@ -391,7 +404,8 @@ func subU(x int64, y uint64) int64 {
 		x -= 1
 		y -= 1 << 63
 	}
-	if subWillUnderflow(x, int64(y)) {
+	// TODO(1.27): investigate passing a smaller-magnitude underflow limit in here.
+	if subWillUnderflow(x, int64(y), minSignedValue(types.Types[types.TINT64])) {
 		base.Fatalf("subU underflowed %d - %d", x, y)
 	}
 	return x - int64(y)