Merge pull request #21305 from hvitved/rust/type-inference-speedup

Rust: Speedup `inferMethodCallTypeSelf`

Author: hvitved

rust/ql/lib/codeql/rust/internal/typeinference/TypeInference.qll

@@ -2477,10 +2477,10 @@ private module MethodCallMatchingInput implements MatchingWithEnvironmentInputSi
   additional predicate decodeDerefChainBorrow(
     string derefChainBorrow, DerefChain derefChain, BorrowKind borrow
   ) {
-    exists(string regexp |
-      regexp = "^(.*);(.*)$" and
-      derefChain = derefChainBorrow.regexpCapture(regexp, 1) and
-      borrow.toString() = derefChainBorrow.regexpCapture(regexp, 2)
+    exists(int i |
+      i = derefChainBorrow.indexOf(";") and
+      derefChain = derefChainBorrow.prefix(i) and
+      borrow.toString() = derefChainBorrow.suffix(i + 1)
     )
   }
 
@@ -2604,37 +2604,39 @@ private Type inferMethodCallTypeNonSelf(AstNode n, boolean isReturn, TypePath pa
 }
 
 /**
- * Gets the type of `n` at `path` after applying `derefChain` and `borrow`,
- * where `n` is the `self` argument of a method call.
+ * Gets the type of `n` at `path` after applying `derefChain`, where `n` is the
+ * `self` argument of a method call.
  *
  * The predicate recursively pops the head of `derefChain` until it becomes
  * empty, at which point the inferred type can be applied back to `n`.
  */
 pragma[nomagic]
-private Type inferMethodCallTypeSelf(
-  AstNode n, DerefChain derefChain, BorrowKind borrow, TypePath path
-) {
-  exists(MethodCallMatchingInput::AccessPosition apos, string derefChainBorrow |
-    result = inferMethodCallType0(_, apos, n, derefChainBorrow, path) and
+private Type inferMethodCallTypeSelf(AstNode n, DerefChain derefChain, TypePath path) {
+  exists(
+    MethodCallMatchingInput::AccessPosition apos, string derefChainBorrow, BorrowKind borrow,
+    TypePath path0
+  |
+    result = inferMethodCallType0(_, apos, n, derefChainBorrow, path0) and
     apos.isSelf() and
     MethodCallMatchingInput::decodeDerefChainBorrow(derefChainBorrow, derefChain, borrow)
-  )
-  or
-  // adjust for implicit borrow
-  exists(TypePath path0, BorrowKind borrow0 |
-    result = inferMethodCallTypeSelf(n, derefChain, borrow0, path0) and
-    path0.isCons(borrow0.getRefType().getPositionalTypeParameter(0), path) and
-    borrow.isNoBorrow()
+  |
+    borrow.isNoBorrow() and
+    path = path0
+    or
+    // adjust for implicit borrow
+    exists(TypePath prefix |
+      prefix = TypePath::singleton(borrow.getRefType().getPositionalTypeParameter(0)) and
+      path0 = prefix.appendInverse(path)
+    )
   )
   or
   // adjust for implicit deref
   exists(
     DerefChain derefChain0, Type t0, TypePath path0, DerefImplItemNode impl, Type selfParamType,
     TypePath selfPath
   |
-    t0 = inferMethodCallTypeSelf(n, derefChain0, borrow, path0) and
+    t0 = inferMethodCallTypeSelf(n, derefChain0, path0) and
     derefChain0.isCons(impl, derefChain) and
-    borrow.isNoBorrow() and
     selfParamType = impl.resolveSelfTypeAt(selfPath)
   |
     result = selfParamType and
@@ -2653,7 +2655,7 @@ private Type inferMethodCallTypeSelf(
 private Type inferMethodCallTypePreCheck(AstNode n, boolean isReturn, TypePath path) {
   result = inferMethodCallTypeNonSelf(n, isReturn, path)
   or
-  result = inferMethodCallTypeSelf(n, DerefChain::nil(), TNoBorrowKind(), path) and
+  result = inferMethodCallTypeSelf(n, DerefChain::nil(), path) and
   isReturn = false
 }
 

shared/util/codeql/util/UnboundList.qll

@@ -78,6 +78,9 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     /** Holds if this list is empty. */
     predicate isEmpty() { this = "" }
 
+    bindingset[this]
+    private int stringLength() { result = super.length() }
+
     /** Gets the length of this list. */
     bindingset[this]
     pragma[inline_late]
@@ -115,19 +118,23 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     /** Holds if this list starts with `e`, followed by `suffix`. */
     bindingset[this]
     predicate isCons(Element e, UnboundList suffix) {
-      exists(string regexp | regexp = "^([0-9]+)\\.(.*)$" |
-        e = decode(this.regexpCapture(regexp, 1)) and
-        suffix = this.regexpCapture(regexp, 2)
+      exists(string elem |
+        // it is more efficient to not create a capture group for the suffix, since
+        // `regexpCapture` will then always join in both groups, only to afterwards filter
+        // based on the requested group (the group number is not part of the binding set
+        // of `regexpCapture`)
+        elem = this.regexpCapture("^([0-9]+)\\..*$", 1) and
+        e = decode(elem) and
+        suffix = this.suffix(elem.length() + 1)
       )
     }
 
     /** Holds if this list starts with `prefix`, followed by `e`. */
     bindingset[this]
     predicate isSnoc(UnboundList prefix, Element e) {
-      exists(string regexp | regexp = "^(|.+\\.)([0-9]+)\\.$" |
-        prefix = this.regexpCapture(regexp, 1) and
-        e = decode(this.regexpCapture(regexp, 2))
-      )
+      // same remark as above about not using multiple capture groups
+      prefix = this.regexpCapture("^(|.+\\.)[0-9]+\\.$", 1) and
+      e = decode(this.substring(prefix.stringLength(), this.stringLength() - 1))
     }
 
     /** Gets the head of this list, if any. */