fix(analyzers): avoid SSA dependency cycle blowups in issue #1555 paths (#1559)

Route redirect dependency checks through the cycle-safe
dependencyChecker instead of raw recursive valueDependsOn traversal.
This ensures Phi-cycle graphs terminate quickly and avoids recursive
work amplification that can look like hangs on large/generated
codebases.

Also remove the nil fallback in dependencyChecker.dependsOn so all
analyzer paths consistently use cycle-aware logic.

Add regression tests covering raw valueDependsOn behavior on:

Phi cycle without target (must return false)
Phi cycle with target path (must return true)
Self-referential Phi node (must return false)

Signed-off-by: Cosmin Cojocar <cosmin@cojocar.ch>

analyzers/form_parsing_limits.go

@@ -46,9 +46,6 @@ func newDependencyChecker() *dependencyChecker {
 }
 
 func (c *dependencyChecker) dependsOn(value ssa.Value, target ssa.Value) bool {
-	if c == nil {
-		return valueDependsOn(value, target, 0)
-	}
 	return c.dependsOnDepth(value, target, 0)
 }
 

analyzers/form_parsing_limits_internal_test.go

@@ -43,3 +43,50 @@ func TestDependencyCheckerFindsTargetInPhiCycle(t *testing.T) {
 		t.Fatal("expected stable memoized result on repeated call")
 	}
 }
+
+func TestValueDependsOnHandlesPhiCycleWithoutTarget(t *testing.T) {
+	t.Parallel()
+
+	target := ssa.NewConst(constant.MakeInt64(42), types.Typ[types.Int])
+
+	phiA := &ssa.Phi{}
+	phiB := &ssa.Phi{}
+	phiA.Edges = []ssa.Value{phiB}
+	phiB.Edges = []ssa.Value{phiA}
+
+	if valueDependsOn(phiA, target, 0) {
+		t.Fatal("expected false for Phi cycle with no path to target")
+	}
+}
+
+func TestValueDependsOnFindsTargetInPhiCycle(t *testing.T) {
+	t.Parallel()
+
+	target := ssa.NewConst(constant.MakeInt64(7), types.Typ[types.Int])
+
+	phiA := &ssa.Phi{}
+	phiB := &ssa.Phi{}
+	phiA.Edges = []ssa.Value{phiB, target}
+	phiB.Edges = []ssa.Value{phiA}
+
+	if !valueDependsOn(phiA, target, 0) {
+		t.Fatal("expected true when cycle has a path to target")
+	}
+
+	if !valueDependsOn(phiA, target, 0) {
+		t.Fatal("expected stable result on repeated call")
+	}
+}
+
+func TestValueDependsOnSelfReferentialPhi(t *testing.T) {
+	t.Parallel()
+
+	target := ssa.NewConst(constant.MakeInt64(1), types.Typ[types.Int])
+
+	phi := &ssa.Phi{}
+	phi.Edges = []ssa.Value{phi}
+
+	if valueDependsOn(phi, target, 0) {
+		t.Fatal("expected false for self-referential Phi with no path to target")
+	}
+}

analyzers/redirect_header_propagation.go

@@ -261,61 +261,6 @@ func extractStringConst(v ssa.Value) string {
 }
 
 func valueDependsOn(value ssa.Value, target ssa.Value, depth int) bool {
-	if value == nil || target == nil || depth > MaxDepth {
-		return false
-	}
-	if value == target {
-		return true
-	}
-
-	switch v := value.(type) {
-	case *ssa.ChangeType:
-		return valueDependsOn(v.X, target, depth+1)
-	case *ssa.MakeInterface:
-		return valueDependsOn(v.X, target, depth+1)
-	case *ssa.TypeAssert:
-		return valueDependsOn(v.X, target, depth+1)
-	case *ssa.UnOp:
-		return valueDependsOn(v.X, target, depth+1)
-	case *ssa.FieldAddr:
-		return valueDependsOn(v.X, target, depth+1)
-	case *ssa.Field:
-		return valueDependsOn(v.X, target, depth+1)
-	case *ssa.IndexAddr:
-		return valueDependsOn(v.X, target, depth+1) || valueDependsOn(v.Index, target, depth+1)
-	case *ssa.Index:
-		return valueDependsOn(v.X, target, depth+1) || valueDependsOn(v.Index, target, depth+1)
-	case *ssa.Slice:
-		if valueDependsOn(v.X, target, depth+1) {
-			return true
-		}
-		if v.Low != nil && valueDependsOn(v.Low, target, depth+1) {
-			return true
-		}
-		if v.High != nil && valueDependsOn(v.High, target, depth+1) {
-			return true
-		}
-		return v.Max != nil && valueDependsOn(v.Max, target, depth+1)
-	case *ssa.Extract:
-		return valueDependsOn(v.Tuple, target, depth+1)
-	case *ssa.Phi:
-		for _, edge := range v.Edges {
-			if valueDependsOn(edge, target, depth+1) {
-				return true
-			}
-		}
-		return false
-	case *ssa.Call:
-		if v.Call.Value != nil && valueDependsOn(v.Call.Value, target, depth+1) {
-			return true
-		}
-		for _, arg := range v.Call.Args {
-			if valueDependsOn(arg, target, depth+1) {
-				return true
-			}
-		}
-		return false
-	default:
-		return false
-	}
+	checker := newDependencyChecker()
+	return checker.dependsOnDepth(value, target, depth)
 }