Make Go use the shared SSA library (codeql.ssa.Ssa)

Co-authored-by: owen-mc <62447351+owen-mc@users.noreply.github.com>
Agent-Logs-Url: https://github.com/github/codeql/sessions/b400ebd5-4095-401e-8811-fb550600b3c4

Author: Copilot

go/ql/lib/change-notes/2026-03-23-use-shared-ssa.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The Go SSA library now uses the shared SSA library (`codeql.ssa.Ssa`), consistent with other CodeQL languages such as C#, Java, Ruby, Rust, and Swift. This may result in minor changes to SSA construction in some edge cases.

go/ql/lib/qlpack.yml

@@ -10,6 +10,7 @@ dependencies:
   codeql/controlflow: ${workspace}
   codeql/dataflow: ${workspace}
   codeql/mad: ${workspace}
+  codeql/ssa: ${workspace}
   codeql/threat-models: ${workspace}
   codeql/tutorial: ${workspace}
   codeql/util: ${workspace}

go/ql/lib/semmle/go/controlflow/BasicBlocks.qll

@@ -48,6 +48,17 @@ class BasicBlock = BbImpl::BasicBlock;
 
 class EntryBasicBlock = BbImpl::EntryBasicBlock;
 
+/** Provides a `CfgSig` view of Go's control-flow graph for use with the shared SSA library. */
+module Cfg implements BB::CfgSig<Location> {
+  class ControlFlowNode = BbImpl::ControlFlowNode;
+
+  class BasicBlock = BbImpl::BasicBlock;
+
+  class EntryBasicBlock = BbImpl::EntryBasicBlock;
+
+  predicate dominatingEdge = BbImpl::dominatingEdge/2;
+}
+
 cached
 private predicate reachableBB(BasicBlock bb) {
   bb instanceof EntryBasicBlock

go/ql/lib/semmle/go/dataflow/SSA.qll

@@ -63,9 +63,9 @@ private predicate unresolvedIdentifier(Ident id, string name) {
 /**
  * An SSA variable.
  */
-class SsaVariable extends TSsaDefinition {
+class SsaVariable extends Definition {
   /** Gets the source variable corresponding to this SSA variable. */
-  SsaSourceVariable getSourceVariable() { result = this.(SsaDefinition).getSourceVariable() }
+  SsaSourceVariable getSourceVariable() { this.definesAt(result, _, _) }
 
   /** Gets the (unique) definition of this SSA variable. */
   SsaDefinition getDefinition() { result = this }
@@ -74,21 +74,31 @@ class SsaVariable extends TSsaDefinition {
   Type getType() { result = this.getSourceVariable().getType() }
 
   /** Gets a use in basic block `bb` that refers to this SSA variable. */
-  IR::Instruction getAUseIn(ReachableBasicBlock bb) {
+  IR::Instruction getAUseIn(BasicBlock bb) {
     exists(int i, SsaSourceVariable v | v = this.getSourceVariable() |
       result = bb.getNode(i) and
-      this = getDefinition(bb, i, v)
+      ssaDefReachesRead(v, this, bb, i) and
+      useAt(bb, i, v)
     )
   }
 
   /** Gets a use that refers to this SSA variable. */
   IR::Instruction getAUse() { result = this.getAUseIn(_) }
 
-  /** Gets a textual representation of this element. */
-  string toString() { result = this.getDefinition().prettyPrintRef() }
+  /**
+   * Gets a textual representation of this element.
+   *
+   * The format is `kind@LINE:COL`, where `kind` is one of `def`, `capture`, or `phi`.
+   */
+  override string toString() {
+    exists(Location loc | loc = this.(SsaDefinition).getLocation() |
+      result =
+        this.(SsaDefinition).getKind() + "@" + loc.getStartLine() + ":" + loc.getStartColumn()
+    )
+  }
 
   /** Gets the location of this SSA variable. */
-  Location getLocation() { result = this.getDefinition().getLocation() }
+  Location getLocation() { result = this.(SsaDefinition).getLocation() }
 
   /**
    * DEPRECATED: Use `getLocation()` instead.
@@ -109,50 +119,28 @@ class SsaVariable extends TSsaDefinition {
 /**
  * An SSA definition.
  */
-class SsaDefinition extends TSsaDefinition {
+class SsaDefinition extends Definition {
   /** Gets the SSA variable defined by this definition. */
   SsaVariable getVariable() { result = this }
 
   /** Gets the source variable defined by this definition. */
-  abstract SsaSourceVariable getSourceVariable();
+  SsaSourceVariable getSourceVariable() { this.definesAt(result, _, _) }
 
   /**
    * Gets the basic block to which this definition belongs.
    */
-  abstract ReachableBasicBlock getBasicBlock();
+  BasicBlock getBasicBlock() { this.definesAt(_, result, _) }
 
-  /**
-   * INTERNAL: Use `getBasicBlock()` and `getSourceVariable()` instead.
-   *
-   * Holds if this is a definition of source variable `v` at index `idx` in basic block `bb`.
-   *
-   * Phi nodes are considered to be at index `-1`, all other definitions at the index of
-   * the control flow node they correspond to.
-   */
-  abstract predicate definesAt(ReachableBasicBlock bb, int idx, SsaSourceVariable v);
-
-  /**
-   * INTERNAL: Use `toString()` instead.
-   *
-   * Gets a pretty-printed representation of this SSA definition.
-   */
-  abstract string prettyPrintDef();
+  /** Gets the innermost function or file to which this SSA definition belongs. */
+  ControlFlow::Root getRoot() { result = this.getBasicBlock().getScope() }
 
   /**
    * INTERNAL: Do not use.
    *
-   * Gets a pretty-printed representation of a reference to this SSA definition.
+   * Gets a short string identifying the kind of this SSA definition,
+   * used in reference formatting (e.g., `"def"`, `"capture"`, `"phi"`).
    */
-  abstract string prettyPrintRef();
-
-  /** Gets the innermost function or file to which this SSA definition belongs. */
-  ControlFlow::Root getRoot() { result = this.getBasicBlock().getScope() }
-
-  /** Gets a textual representation of this element. */
-  string toString() { result = this.prettyPrintDef() }
-
-  /** Gets the source location for this element. */
-  abstract Location getLocation();
+  string getKind() { none() }
 
   /**
    * DEPRECATED: Use `getLocation()` instead.
@@ -180,32 +168,25 @@ class SsaDefinition extends TSsaDefinition {
 /**
  * An SSA definition that corresponds to an explicit assignment or other variable definition.
  */
-class SsaExplicitDefinition extends SsaDefinition, TExplicitDef {
+class SsaExplicitDefinition extends SsaDefinition, WriteDefinition {
+  SsaExplicitDefinition() {
+    exists(BasicBlock bb, int i, SsaSourceVariable v |
+      this.definesAt(v, bb, i) and
+      defAt(bb, i, v)
+    )
+  }
+
   /** Gets the instruction where the definition happens. */
   IR::Instruction getInstruction() {
-    exists(BasicBlock bb, int i | this = TExplicitDef(bb, i, _) | result = bb.getNode(i))
+    exists(BasicBlock bb, int i | this.definesAt(_, bb, i) | result = bb.getNode(i))
   }
 
   /** Gets the right-hand side of the definition. */
   IR::Instruction getRhs() { this.getInstruction().writes(_, result) }
 
-  override predicate definesAt(ReachableBasicBlock bb, int i, SsaSourceVariable v) {
-    this = TExplicitDef(bb, i, v)
-  }
-
-  override ReachableBasicBlock getBasicBlock() { this.definesAt(result, _, _) }
-
-  override SsaSourceVariable getSourceVariable() { this = TExplicitDef(_, _, result) }
-
-  override string prettyPrintRef() {
-    exists(Location loc | loc = this.getLocation() |
-      result = "def@" + loc.getStartLine() + ":" + loc.getStartColumn()
-    )
-  }
+  override string getKind() { result = "def" }
 
-  override string prettyPrintDef() { result = "definition of " + this.getSourceVariable() }
-
-  override Location getLocation() { result = this.getInstruction().getLocation() }
+  override string toString() { result = "definition of " + this.getSourceVariable() }
 }
 
 /** Provides a helper predicate for working with explicit SSA definitions. */
@@ -220,19 +201,6 @@ module SsaExplicitDefinition {
  * An SSA definition that does not correspond to an explicit variable definition.
  */
 abstract class SsaImplicitDefinition extends SsaDefinition {
-  /**
-   * INTERNAL: Do not use.
-   *
-   * Gets the definition kind to include in `prettyPrintRef`.
-   */
-  abstract string getKind();
-
-  override string prettyPrintRef() {
-    exists(Location loc | loc = this.getLocation() |
-      result = this.getKind() + "@" + loc.getStartLine() + ":" + loc.getStartColumn()
-    )
-  }
-
   override Location getLocation() { result = this.getBasicBlock().getLocation() }
 }
 
@@ -243,24 +211,16 @@ abstract class SsaImplicitDefinition extends SsaDefinition {
  * Capturing definitions appear at the beginning of such functions, as well as
  * at any function call that may affect the value of the variable.
  */
-class SsaVariableCapture extends SsaImplicitDefinition, TCapture {
-  override predicate definesAt(ReachableBasicBlock bb, int i, SsaSourceVariable v) {
-    this = TCapture(bb, i, v)
-  }
-
-  override ReachableBasicBlock getBasicBlock() { this.definesAt(result, _, _) }
-
-  override SsaSourceVariable getSourceVariable() { this.definesAt(_, _, result) }
-
-  override string getKind() { result = "capture" }
-
-  override string prettyPrintDef() { result = "capture variable " + this.getSourceVariable() }
-
+class SsaVariableCapture extends SsaImplicitDefinition, UncertainWriteDefinition {
   override Location getLocation() {
-    exists(ReachableBasicBlock bb, int i | this.definesAt(bb, i, _) |
+    exists(BasicBlock bb, int i | this.definesAt(_, bb, i) |
       result = bb.getNode(i).getLocation()
     )
   }
+
+  override string getKind() { result = "capture" }
+
+  override string toString() { result = "capture variable " + this.getSourceVariable() }
 }
 
 /**
@@ -277,34 +237,25 @@ abstract class SsaPseudoDefinition extends SsaImplicitDefinition {
    * Gets a textual representation of the inputs of this pseudo-definition
    * in lexicographical order.
    */
-  string ppInputs() { result = concat(this.getAnInput().getDefinition().prettyPrintRef(), ", ") }
+  string ppInputs() {
+    result =
+      concat(SsaVariable inp | inp = this.getAnInput() | inp.toString() order by inp.toString())
+  }
 }
 
 /**
  * An SSA phi node, that is, a pseudo-definition for a variable at a point
  * in the flow graph where otherwise two or more definitions for the variable
  * would be visible.
  */
-class SsaPhiNode extends SsaPseudoDefinition, TPhi {
-  override SsaVariable getAnInput() {
-    result = getDefReachingEndOf(this.getBasicBlock().getAPredecessor(_), this.getSourceVariable())
-  }
-
-  override predicate definesAt(ReachableBasicBlock bb, int i, SsaSourceVariable v) {
-    bb = this.getBasicBlock() and v = this.getSourceVariable() and i = -1
-  }
-
-  override ReachableBasicBlock getBasicBlock() { this = TPhi(result, _) }
-
-  override SsaSourceVariable getSourceVariable() { this = TPhi(_, result) }
+class SsaPhiNode extends SsaPseudoDefinition, PhiNode {
+  override SsaVariable getAnInput() { phiHasInputFromBlock(this, result, _) }
 
   override string getKind() { result = "phi" }
 
-  override string prettyPrintDef() {
+  override string toString() {
     result = this.getSourceVariable() + " = phi(" + this.ppInputs() + ")"
   }
-
-  override Location getLocation() { result = this.getBasicBlock().getLocation() }
 }
 
 /**