Merge pull request #203 from dave-bartolomeo/dave/GVN

C++: Initial attempt at IR-based value numbering

Author: rdmarsh2

config/identical-files.json

@@ -54,5 +54,10 @@
     "C++ SSA SSAConstruction": [
         "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/SSAConstruction.qll",
         "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SSAConstruction.qll"
+    ],
+    "C++ IR ValueNumber": [
+        "cpp/ql/src/semmle/code/cpp/ir/implementation/raw/gvn/ValueNumbering.qll",
+        "cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/gvn/ValueNumbering.qll",
+        "cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/gvn/ValueNumbering.qll"
     ]
 }

cpp/ql/src/semmle/code/cpp/ir/PrintIR.qll

@@ -0,0 +1 @@
+import implementation.aliased_ssa.PrintIR

cpp/ql/src/semmle/code/cpp/ir/ValueNumbering.qll

@@ -0,0 +1 @@
+import implementation.aliased_ssa.gvn.ValueNumbering

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IR.qll

@@ -5,3 +5,30 @@ import IRVariable
 import OperandTag
 import semmle.code.cpp.ir.implementation.EdgeKind
 import semmle.code.cpp.ir.implementation.MemoryAccessKind
+
+private newtype TIRPropertyProvider = MkIRPropertyProvider()
+
+/**
+ * Class that provides additional properties to be dumped for IR instructions and blocks when using
+ * the PrintIR module. Libraries that compute additional facts about IR elements can extend the
+ * single instance of this class to specify the additional properties computed by the library.
+ */
+class IRPropertyProvider extends TIRPropertyProvider {
+  string toString() {
+    result = "IRPropertyProvider"
+  }
+
+  /**
+   * Gets the value of the property named `key` for the specified instruction.
+   */
+  string getInstructionProperty(Instruction instruction, string key) {
+    none()
+  }
+
+  /**
+   * Gets the value of the property named `key` for the specified block.
+   */
+  string getBlockProperty(IRBlock block, string key) {
+    none()
+  }
+}

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/Instruction.qll

@@ -107,6 +107,14 @@ module InstructionSanity {
     operand = op.getOperand(tag) and
     operand.getFunctionIR() != op.getFunctionIR()
   }
+
+  /**
+   * Holds if instruction `instr` is not in exactly one block.
+   */
+  query predicate instructionWithoutUniqueBlock(Instruction instr, int blockCount) {
+    blockCount = count(instr.getBlock()) and
+    blockCount != 1
+  } 
 }
 
 /**
@@ -301,6 +309,13 @@ class Instruction extends Construction::TInstruction {
     result = ast.getLocation()
   }
 
+  /**
+   * Gets the `Expr` whose results is computed by this instruction, if any.
+   */
+  final Expr getResultExpression() {
+    result = Construction::getInstructionResultExpression(this) 
+  }
+
   /**
    * Gets the type of the result produced by this instruction. If the
    * instruction does not produce a result, its result type will be `VoidType`.
@@ -554,6 +569,15 @@ class InitializeParameterInstruction extends VariableInstruction {
   }
 }
 
+/**
+ * An instruction that initializes the `this` pointer parameter of the enclosing function.
+ */
+class InitializeThisInstruction extends Instruction {
+  InitializeThisInstruction() {
+    opcode instanceof Opcode::InitializeThis
+  }
+}
+
 class FieldAddressInstruction extends FieldInstruction {
   FieldAddressInstruction() {
     opcode instanceof Opcode::FieldAddress

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/PrintIR.qll

@@ -1,6 +1,18 @@
 private import IR
 import cpp
 
+private string getAdditionalInstructionProperty(Instruction instr, string key) {
+  exists(IRPropertyProvider provider |
+    result = provider.getInstructionProperty(instr, key)
+  )
+}
+
+private string getAdditionalBlockProperty(IRBlock block, string key) {
+  exists(IRPropertyProvider provider |
+    result = provider.getBlockProperty(block, key)
+  )
+}
+
 private newtype TPrintableIRNode =
   TPrintableFunctionIR(FunctionIR funcIR) or
   TPrintableIRBlock(IRBlock block) or
@@ -135,6 +147,11 @@ class PrintableIRBlock extends PrintableIRNode, TPrintableIRBlock {
     result.getFunctionIR() = block.getFunctionIR()
   }
 
+  override string getProperty(string key) {
+    result = PrintableIRNode.super.getProperty(key) or
+    result = getAdditionalBlockProperty(block, key)
+  }
+
   final IRBlock getBlock() {
     result = block
   }
@@ -185,6 +202,11 @@ class PrintableInstruction extends PrintableIRNode, TPrintableInstruction {
   final Instruction getInstruction() {
     result = instr
   }
+
+  override string getProperty(string key) {
+    result = PrintableIRNode.super.getProperty(key) or
+    result = getAdditionalInstructionProperty(instr, key)
+  }
 }
 
 private predicate columnWidths(IRBlock block, int resultWidth, int operationWidth) {