C++: Remove Phi instructions from previous IR generations

It turns out that when building aliased SSA IR, we were still keeping around the Phi instructions from unaliased SSA IR. These leftover instructions didn't show up in dumps because they were not assigned to a block. However, when dumping additional instruction properties, they would show up as a top-level node in the dump, without a label.

Author: dave-bartolomeo

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
+  } 
 }
 
 /**

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

@@ -30,7 +30,9 @@ cached private module Cached {
   }
 
   cached newtype TInstructionTag =
-    WrappedInstructionTag(OldIR::Instruction oldInstruction) or
+    WrappedInstructionTag(OldIR::Instruction oldInstruction) {
+      not oldInstruction instanceof OldIR::PhiInstruction
+    } or
     PhiTag(Alias::VirtualVariable vvar, OldIR::IRBlock block) {
       hasPhiNode(vvar, block)
     }

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/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
+  } 
 }
 
 /**

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_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
+  } 
 }
 
 /**

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

@@ -30,7 +30,9 @@ cached private module Cached {
   }
 
   cached newtype TInstructionTag =
-    WrappedInstructionTag(OldIR::Instruction oldInstruction) or
+    WrappedInstructionTag(OldIR::Instruction oldInstruction) {
+      not oldInstruction instanceof OldIR::PhiInstruction
+    } or
     PhiTag(Alias::VirtualVariable vvar, OldIR::IRBlock block) {
       hasPhiNode(vvar, block)
     }

cpp/ql/test/library-tests/ir/ir/aliased_ssa_sanity.expected

@@ -5,3 +5,4 @@ missingPhiOperand
 instructionWithoutSuccessor
 unnecessaryPhiInstruction
 operandAcrossFunctions
+instructionWithoutUniqueBlock

cpp/ql/test/library-tests/ir/ir/raw_sanity.expected

@@ -5,3 +5,4 @@ missingPhiOperand
 instructionWithoutSuccessor
 unnecessaryPhiInstruction
 operandAcrossFunctions
+instructionWithoutUniqueBlock

cpp/ql/test/library-tests/ir/ir/unaliased_ssa_sanity.expected

@@ -5,3 +5,4 @@ missingPhiOperand
 instructionWithoutSuccessor
 unnecessaryPhiInstruction
 operandAcrossFunctions
+instructionWithoutUniqueBlock

cpp/ql/test/library-tests/valuenumbering/GlobalValueNumbering/ir_gvn.expected

@@ -67,15 +67,6 @@ test.cpp:
 #    1|     v0_33(void)                 = UnmodeledUse             : mu*
 #    1|     v0_34(void)                 = ExitFunction             : 
 
-#   53| 1644
-#   53|     valnum = unique
-
-#   56| 1646
-#   56|     valnum = unique
-
-#   88| 1755
-#   88|     valnum = unique
-
 #   12| test01(int, int) -> int
 #   12|   Block 0
 #   12|     v0_0(void)                  = EnterFunction             :