Util: Only compute dense ranks when needed

shared/util/codeql/util/DenseRank.qll

@@ -55,13 +55,33 @@ signature module DenseRankInputSig {
 module DenseRank<DenseRankInputSig Input> {
   private import Input
 
+  private int getARank() { result = getRank(_) }
+
+  pragma[noinline]
+  private int getARankGap() { result = getARank() and not result - 1 = getARank() }
+
+  pragma[noinline]
+  private predicate isDenseFrom(int i) { i = unique( | | getARankGap()) }
+
+  pragma[noinline]
+  private int getRankNeedsDenseRank(Ranked r) { result = getRank(r) and not isDenseFrom(_) }
+
   private int rankRank(Ranked r, int rnk) {
-    rnk = getRank(r) and
-    rnk = rank[result](int rnk0 | rnk0 = getRank(_) | rnk0)
+    rnk = getRankNeedsDenseRank(r) and
+    rnk = rank[result](int rnk0 | rnk0 = getRankNeedsDenseRank(_) | rnk0)
   }
 
   /** Gets the `Ranked` value for which the dense rank is `rnk`. */
-  Ranked denseRank(int rnk) { rnk = rankRank(result, getRank(result)) }
+  pragma[nomagic]
+  Ranked denseRank(int rnk) {
+    rnk = rankRank(result, getRankNeedsDenseRank(result))
+    or
+    exists(int i, int offset |
+      isDenseFrom(i) and
+      offset = i - 1 and
+      rnk = getRank(result) - offset
+    )
+  }
 }
 
 /** Provides the input to `DenseRank1`. */
@@ -82,16 +102,38 @@ signature module DenseRankInputSig1 {
 module DenseRank1<DenseRankInputSig1 Input> {
   private import Input
 
+  private int getARank(C c) { result = getRank(c, _) }
+
+  pragma[noinline]
+  private int getARankGap(C c) { result = getARank(c) and not result - 1 = getARank(c) }
+
+  pragma[noinline]
+  private predicate isDenseFrom(C c, int i) { i = unique( | | getARankGap(c)) }
+
+  pragma[noinline]
+  private int getRankNeedsDenseRank(C c, Ranked r) {
+    result = getRank(c, r) and not isDenseFrom(c, _)
+  }
+
   private int rankRank(C c, Ranked r, int rnk) {
-    rnk = getRank(c, r) and
-    rnk = rank[result](int rnk0 | rnk0 = getRank(c, _) | rnk0)
+    rnk = getRankNeedsDenseRank(c, r) and
+    rnk = rank[result](int rnk0 | rnk0 = getRankNeedsDenseRank(c, _) | rnk0)
   }
 
   /**
    * Gets the `Ranked` value for which the dense rank in the context provided by
    * `c` is `rnk`.
    */
-  Ranked denseRank(C c, int rnk) { rnk = rankRank(c, result, getRank(c, result)) }
+  pragma[nomagic]
+  Ranked denseRank(C c, int rnk) {
+    rnk = rankRank(c, result, getRankNeedsDenseRank(c, result))
+    or
+    exists(int i, int offset |
+      isDenseFrom(c, i) and
+      offset = i - 1 and
+      rnk = getRank(c, result) - offset
+    )
+  }
 }
 
 /** Provides the input to `DenseRank2`. */
@@ -116,16 +158,38 @@ signature module DenseRankInputSig2 {
 module DenseRank2<DenseRankInputSig2 Input> {
   private import Input
 
+  private int getARank(C1 c1, C2 c2) { result = getRank(c1, c2, _) }
+
+  pragma[noinline]
+  private int getARankGap(C1 c1, C2 c2) {
+    result = getARank(c1, c2) and not result - 1 = getARank(c1, c2)
+  }
+
+  pragma[noinline]
+  private predicate isDenseFrom(C1 c1, C2 c2, int i) { i = unique( | | getARankGap(c1, c2)) }
+
+  pragma[noinline]
+  private int getRankNeedsDenseRank(C1 c1, C2 c2, Ranked r) {
+    result = getRank(c1, c2, r) and not isDenseFrom(c1, c2, _)
+  }
+
   private int rankRank(C1 c1, C2 c2, Ranked r, int rnk) {
-    rnk = getRank(c1, c2, r) and
-    rnk = rank[result](int rnk0 | rnk0 = getRank(c1, c2, _) | rnk0)
+    rnk = getRankNeedsDenseRank(c1, c2, r) and
+    rnk = rank[result](int rnk0 | rnk0 = getRankNeedsDenseRank(c1, c2, _) | rnk0)
   }
 
   /**
    * Gets the `Ranked` value for which the dense rank in the context provided by
    * `c1` and `c2` is `rnk`.
    */
+  pragma[nomagic]
   Ranked denseRank(C1 c1, C2 c2, int rnk) {
-    rnk = rankRank(c1, c2, result, getRank(c1, c2, result))
+    rnk = rankRank(c1, c2, result, getRankNeedsDenseRank(c1, c2, result))
+    or
+    exists(int i, int offset |
+      isDenseFrom(c1, c2, i) and
+      offset = i - 1 and
+      rnk = getRank(c1, c2, result) - offset
+    )
   }
 }