Merge pull request github#5051 from hvitved/csharp/ssa/caching

C#: Reduce caching in `SsaImplCommon.qll`

Author: hvitved

csharp/ql/src/semmle/code/csharp/dataflow/SSA.qll

@@ -176,6 +176,16 @@ module Ssa {
       exists(ControlFlow::BasicBlock bb, int i | this.definesAt(_, bb, i) | result = bb.getNode(i))
     }
 
+    /**
+     * Holds is this SSA definition is live at the end of basic block `bb`.
+     * That is, this definition reaches the end of basic block `bb`, at which
+     * point it is still live, without crossing another SSA definition of the
+     * same source variable.
+     */
+    final predicate isLiveAtEndOfBlock(ControlFlow::BasicBlock bb) {
+      SsaImpl::isLiveAtEndOfBlock(this, bb)
+    }
+
     /**
      * Gets a read of the source variable underlying this SSA definition that
      * can be reached from this SSA definition without passing through any
@@ -233,12 +243,7 @@ module Ssa {
      *   node between lines 9 and 10.
      */
     final AssignableRead getAReadAtNode(ControlFlow::Node cfn) {
-      exists(SourceVariable v, ControlFlow::BasicBlock bb, int i |
-        SsaImpl::ssaDefReachesRead(v, this, bb, i) and
-        SsaImpl::variableReadActual(bb, i, v) and
-        cfn = bb.getNode(i) and
-        result.getAControlFlowNode() = cfn
-      )
+      result = SsaImpl::getAReadAtNode(this, cfn)
     }
 
     /**

csharp/ql/src/semmle/code/csharp/dataflow/internal/SsaImpl.qll

@@ -8,7 +8,7 @@ import SsaImplCommon
 /**
  * Holds if the `i`th node of basic block `bb` reads source variable `v`.
  */
-predicate variableReadActual(ControlFlow::BasicBlock bb, int i, Ssa::SourceVariable v) {
+private predicate variableReadActual(ControlFlow::BasicBlock bb, int i, Ssa::SourceVariable v) {
   v.getAnAccess().(AssignableRead) = bb.getNode(i).getElement()
 }
 
@@ -1102,6 +1102,11 @@ private module Cached {
     )
   }
 
+  cached
+  predicate isLiveAtEndOfBlock(Definition def, ControlFlow::BasicBlock bb) {
+    ssaDefReachesEndOfBlock(bb, def, _)
+  }
+
   private predicate adjacentDefReaches(
     Definition def, ControlFlow::BasicBlock bb1, int i1, ControlFlow::BasicBlock bb2, int i2
   ) {
@@ -1122,6 +1127,16 @@ private module Cached {
     variableReadActual(bb2, i2, _)
   }
 
+  cached
+  AssignableRead getAReadAtNode(Definition def, ControlFlow::Node cfn) {
+    exists(Ssa::SourceVariable v, ControlFlow::BasicBlock bb, int i |
+      ssaDefReachesRead(v, def, bb, i) and
+      variableReadActual(bb, i, v) and
+      cfn = bb.getNode(i) and
+      result.getAControlFlowNode() = cfn
+    )
+  }
+
   /**
    * Holds if the value defined at SSA definition `def` can reach a read at `cfn`,
    * without passing through any other read.