C++: fixups and file sync for SSA sharing

Author: Robert Marsh

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/AliasAnalysis.qll

@@ -329,9 +329,7 @@ predicate allocationEscapes(Configuration::Allocation allocation) {
     config.useSoundEscapeAnalysis() and resultEscapesNonReturn(allocation.getABaseInstruction())
   )
   or
-  exists(Configuration::StageEscapeConfiguration config |
-    config.useSoundEscapeAnalysis() and resultEscapesNonReturn(allocation.getABaseInstruction())
-  )
+  Configuration::phaseNeedsSoundEscapeAnalysis() and resultEscapesNonReturn(allocation.getABaseInstruction())
 }
 
 /**

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/AliasConfiguration.qll

@@ -143,8 +143,4 @@ class DynamicAllocation extends Allocation, TDynamicAllocation {
   final override predicate alwaysEscapes() { none() }
 }
 
-class StageEscapeConfiguration extends string {
-  StageEscapeConfiguration() { this = "StageEscapeConfiguration (aliased_ssa)" }
-
-  predicate useSoundEscapeAnalysis() { none() }
-}
+predicate phaseNeedsSoundEscapeAnalysis() { none() }

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/AliasedSSA.qll

@@ -133,7 +133,7 @@ abstract class MemoryLocation extends TMemoryLocation {
    */
   predicate isAlwaysAllocatedOnStack() { none() }
 
-  final predicate canReuseSSA() { any() }
+  final predicate canReuseSSA() { none() }
 }
 
 /**

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SSAConstruction.qll

@@ -60,8 +60,19 @@ private module Cached {
   predicate hasInstruction(TStageInstruction instr) {
     instr instanceof TRawInstruction and instr instanceof OldInstruction
     or
-    instr instanceof TPhiInstruction and 
-    not exists(getDegeneratePhiOperand(instr))
+    instr = phiInstruction(_, _)
+    or
+    instr = reusedPhiInstruction(_) and
+    // Check that the phi instruction is *not* degenerate, but we can't use
+    // getDegeneratePhiOperand in the first stage with phi instyructions
+    exists(OldIR::PhiInputOperand operand1, OldIR::PhiInputOperand operand2, OldInstruction oldInstruction |
+      oldInstruction = instr and
+      operand1 = oldInstruction.(OldIR::PhiInstruction).getAnInputOperand() and
+      operand1.getPredecessorBlock() instanceof OldBlock and
+      operand2 = oldInstruction.(OldIR::PhiInstruction).getAnInputOperand() and
+      operand2.getPredecessorBlock() instanceof OldBlock and
+      operand1 != operand2
+    )
     or
     instr instanceof TChiInstruction
     or

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/AliasAnalysis.qll

@@ -329,9 +329,7 @@ predicate allocationEscapes(Configuration::Allocation allocation) {
     config.useSoundEscapeAnalysis() and resultEscapesNonReturn(allocation.getABaseInstruction())
   )
   or
-  exists(Configuration::StageEscapeConfiguration config |
-    config.useSoundEscapeAnalysis() and resultEscapesNonReturn(allocation.getABaseInstruction())
-  )
+  Configuration::phaseNeedsSoundEscapeAnalysis() and resultEscapesNonReturn(allocation.getABaseInstruction())
 }
 
 /**

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/AliasConfiguration.qll

@@ -15,8 +15,4 @@ class Allocation extends IRAutomaticVariable {
   }
 }
 
-class StageEscapeConfiguration extends string {
-  StageEscapeConfiguration() { this = "StageEscapeConfiguration (unaliased_ssa)" }
-
-  predicate useSoundEscapeAnalysis() { any() }
-}
+predicate phaseNeedsSoundEscapeAnalysis() { any() }

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/SSAConstruction.qll

@@ -43,19 +43,58 @@ private module Cached {
   class TStageInstruction =
     TRawInstruction or TPhiInstruction or TChiInstruction or TUnreachedInstruction;
 
+  /**
+   * If `oldInstruction` is a `Phi` instruction that has exactly one reachable predecessor block,
+   * this predicate returns the `PhiInputOperand` corresponding to that predecessor block.
+   * Otherwise, this predicate does not hold.
+   */
+  private OldIR::PhiInputOperand getDegeneratePhiOperand(OldInstruction oldInstruction) {
+    result =
+      unique(OldIR::PhiInputOperand operand |
+        operand = oldInstruction.(OldIR::PhiInstruction).getAnInputOperand() and
+        operand.getPredecessorBlock() instanceof OldBlock
+      )
+  }
+
   cached
   predicate hasInstruction(TStageInstruction instr) {
     instr instanceof TRawInstruction and instr instanceof OldInstruction
     or
-    instr instanceof TPhiInstruction
+    instr = phiInstruction(_, _)
+    or
+    instr = reusedPhiInstruction(_) and
+    // Check that the phi instruction is *not* degenerate, but we can't use
+    // getDegeneratePhiOperand in the first stage with phi instyructions
+    exists(OldIR::PhiInputOperand operand1, OldIR::PhiInputOperand operand2, OldInstruction oldInstruction |
+      oldInstruction = instr and
+      operand1 = oldInstruction.(OldIR::PhiInstruction).getAnInputOperand() and
+      operand1.getPredecessorBlock() instanceof OldBlock and
+      operand2 = oldInstruction.(OldIR::PhiInstruction).getAnInputOperand() and
+      operand2.getPredecessorBlock() instanceof OldBlock and
+      operand1 != operand2
+    )
     or
     instr instanceof TChiInstruction
     or
     instr instanceof TUnreachedInstruction
   }
 
-  private IRBlock getNewBlock(OldBlock oldBlock) {
-    result.getFirstInstruction() = getNewInstruction(oldBlock.getFirstInstruction())
+  cached IRBlock getNewBlock(OldBlock oldBlock) {
+    exists(Instruction newEnd, OldIR::Instruction oldEnd |
+      (
+      result.getLastInstruction() = newEnd and
+      not newEnd instanceof ChiInstruction
+      or
+      newEnd = result.getLastInstruction().(ChiInstruction).getAPredecessor() // does this work?
+      ) and
+      (
+        oldBlock.getLastInstruction() = oldEnd and
+        not oldEnd instanceof OldIR::ChiInstruction
+        or
+        oldEnd = oldBlock.getLastInstruction().(OldIR::ChiInstruction).getAPredecessor() // does this work?
+      ) and
+      oldEnd = getNewInstruction(newEnd)
+    )
   }
 
   /**
@@ -150,16 +189,13 @@ private module Cached {
       (
         result = getNewInstruction(oldOperand.getAnyDef()) and
         overlap = originalOverlap
-        /*
-         * or
-         *        exists(OldIR::PhiInputOperand phiOperand, Overlap phiOperandOverlap |
-         *          phiOperand = getDegeneratePhiOperand(oldOperand.getAnyDef()) and
-         *          result = getNewDefinitionFromOldSSA(phiOperand, phiOperandOverlap) and
-         *          overlap = combineOverlap(phiOperandOverlap, originalOverlap)
-         *        )
-         */
-
+        or
+        exists(OldIR::PhiInputOperand phiOperand, Overlap phiOperandOverlap |
+          phiOperand = getDegeneratePhiOperand(oldOperand.getAnyDef()) and
+          result = getNewDefinitionFromOldSSA(phiOperand, phiOperandOverlap) and
+          overlap = combineOverlap(phiOperandOverlap, originalOverlap)
         )
+      )
     )
   }