Avoid quadratic switch case intermediate

java/ql/lib/semmle/code/java/ControlFlowGraph.qll

@@ -82,6 +82,7 @@
 import java
 private import Completion
 private import controlflow.internal.Preconditions
+private import controlflow.internal.SwitchCases
 
 /** A node in the expression-level control-flow graph. */
 class ControlFlowNode extends Top, @exprparent {
@@ -436,34 +437,6 @@ private module ControlFlowGraphImpl {
  )
  }
 
- /**
- * Gets the `i`th `SwitchCase` defined on `switch`, if one exists.
- */
- private SwitchCase getCase(StmtParent switch, int i) {
- result = switch.(SwitchExpr).getCase(i) or result = switch.(SwitchStmt).getCase(i)
- }
-
- /**
- * Gets the `i`th `PatternCase` defined on `switch`, if one exists.
- */
- private PatternCase getPatternCase(StmtParent switch, int i) {
- result =
- rank[i + 1](PatternCase pc, int caseIdx | pc = getCase(switch, caseIdx) | pc order by caseIdx)
- }
-
- /**
- * Gets the PatternCase after pc, if one exists.
- */
- private PatternCase getNextPatternCase(PatternCase pc) {
- exists(int idx, StmtParent switch |
- pc = getPatternCase(switch, idx) and result = getPatternCase(switch, idx + 1)
- )
- }
-
- private int lastCaseIndex(StmtParent switch) {
- result = max(int i | any(SwitchCase c).isNthCaseOf(switch, i))
- }
-
  // Join order engineering -- first determine the switch block and the case indices required, then retrieve them.
  bindingset[switch, i]
  pragma[inline_late]

java/ql/lib/semmle/code/java/controlflow/Guards.qll

@@ -7,6 +7,7 @@ import java
 private import semmle.code.java.controlflow.Dominance
 private import semmle.code.java.controlflow.internal.GuardsLogic
 private import semmle.code.java.controlflow.internal.Preconditions
+private import semmle.code.java.controlflow.internal.SwitchCases
 
 /**
  * A basic block that terminates in a condition, splitting the subsequent control flow.
@@ -72,6 +73,35 @@ class ConditionBlock extends BasicBlock {
  }
 }
 
+// Join order engineering -- first determine the switch block and the case indices required, then retrieve them.
+bindingset[switch, i]
+pragma[inline_late]
+private predicate isNthCaseOf(StmtParent switch, SwitchCase c, int i) { c.isNthCaseOf(switch, i) }
+
+/**
+ * Gets a switch case >= pred, up to but not including `pred`'s successor pattern case,
+ * where `pred` is declared on `switch`.
+ */
+private SwitchCase getACaseUpToNextPattern(PatternCase pred, StmtParent switch) {
+ // Note we do include `case null, default` (as well as plain old `default`) here.
+ not result.(ConstCase).getValue(_) instanceof NullLiteral and
+ exists(int maxCaseIndex |
+ switch = pred.getParent() and
+ if exists(getNextPatternCase(pred))
+ then maxCaseIndex = getNextPatternCase(pred).getCaseIndex() - 1
+ else maxCaseIndex = lastCaseIndex(switch)
+ |
+ isNthCaseOf(switch, result, [pred.getCaseIndex() .. maxCaseIndex])
+ )
+}
+
+/**
+ * Gets the closest pattern case preceding `case`, including `case` itself, if any.
+ */
+private PatternCase getClosestPrecedingPatternCase(SwitchCase case) {
+ case = getACaseUpToNextPattern(result, _)
+}
+
 /**
  * A condition that can be evaluated to either true or false. This can either
  * be an `Expr` of boolean type that isn't a boolean literal, or a case of a
@@ -113,17 +143,10 @@ class Guard extends ExprParent {
  result = this.(Expr).getBasicBlock()
  or
  // Return the closest pattern case statement before this one, including this one.
- result =
- max(int i, PatternCase c |
- c = this.(SwitchCase).getSiblingCase(i) and i <= this.(SwitchCase).getCaseIndex()
- |
- c order by i
- ).getBasicBlock()
+ result = getClosestPrecedingPatternCase(this).getBasicBlock()
  or
  // Not a pattern case and no preceding pattern case -- return the top of the switch block.
- not exists(PatternCase c, int i |
- c = this.(SwitchCase).getSiblingCase(i) and i <= this.(SwitchCase).getCaseIndex()
- ) and
+ not exists(getClosestPrecedingPatternCase(this)) and
  result = this.(SwitchCase).getSelectorExpr().getBasicBlock()
  }
 

java/ql/lib/semmle/code/java/controlflow/internal/SwitchCases.qll

@@ -0,0 +1,31 @@
+/** Provides utility predicates relating to switch cases. */
+
+import java
+
+/**
+ * Gets the `i`th `SwitchCase` defined on `switch`, if one exists.
+ */
+SwitchCase getCase(StmtParent switch, int i) {
+ result = switch.(SwitchExpr).getCase(i) or result = switch.(SwitchStmt).getCase(i)
+}
+
+/**
+ * Gets the `i`th `PatternCase` defined on `switch`, if one exists.
+ */
+PatternCase getPatternCase(StmtParent switch, int i) {
+ result =
+ rank[i + 1](PatternCase pc, int caseIdx | pc = getCase(switch, caseIdx) | pc order by caseIdx)
+}
+
+/**
+ * Gets the PatternCase after pc, if one exists.
+ */
+PatternCase getNextPatternCase(PatternCase pc) {
+ exists(int idx, StmtParent switch |
+ pc = getPatternCase(switch, idx) and result = getPatternCase(switch, idx + 1)
+ )
+}
+
+int lastCaseIndex(StmtParent switch) {
+ result = max(int i | any(SwitchCase c).isNthCaseOf(switch, i))
+}