C++: respond to PR comments

Author: Robert Marsh

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

@@ -1475,7 +1475,7 @@ class BufferMayWriteSideEffectInstruction extends SideEffectInstruction {
 }
 
 /**
- * 
+ * An instruction representing a GNU or MSVC inline assembly statement.
  */
 class InlineAsmInstruction extends Instruction {
   InlineAsmInstruction() {

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

@@ -1475,7 +1475,7 @@ class BufferMayWriteSideEffectInstruction extends SideEffectInstruction {
 }
 
 /**
- * 
+ * An instruction representing a GNU or MSVC inline assembly statement.
  */
 class InlineAsmInstruction extends Instruction {
   InlineAsmInstruction() {

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll

@@ -64,6 +64,8 @@ private predicate ignoreExprAndDescendants(Expr expr) {
     // represent them.
     newExpr.getInitializer().getFullyConverted() = expr
   ) or
+  // Ignore descendants of asm statements, since we can't differentiate inputs and outputs
+  getRealParent(expr) instanceof AsmStmt or
   ignoreExprAndDescendants(getRealParent(expr)) // recursive case
 }
 

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

@@ -1475,7 +1475,7 @@ class BufferMayWriteSideEffectInstruction extends SideEffectInstruction {
 }
 
 /**
- * 
+ * An instruction representing a GNU or MSVC inline assembly statement.
  */
 class InlineAsmInstruction extends Instruction {
   InlineAsmInstruction() {

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

@@ -7580,3 +7580,40 @@ ir.cpp:
 # 1101|       0: x
 # 1101|           Type = int
 # 1101|           ValueCategory = prvalue(load)
+# 1104| void AsmStmtWithOutputs(unsigned int&, unsigned int&, unsigned int&, unsigned int&)
+# 1104|   params: 
+# 1104|     0: a
+# 1104|         Type = unsigned int &
+# 1104|     1: b
+# 1104|         Type = unsigned int &
+# 1104|     2: c
+# 1104|         Type = unsigned int &
+# 1104|     3: d
+# 1104|         Type = unsigned int &
+# 1105|   body: { ... }
+# 1107|     0: asm statement
+# 1110|       0: (reference dereference)
+# 1110|           Type = unsigned int
+# 1110|           ValueCategory = lvalue
+# 1110|         expr: a
+# 1110|             Type = unsigned int &
+# 1110|             ValueCategory = prvalue(load)
+# 1110|       1: (reference dereference)
+# 1110|           Type = unsigned int
+# 1110|           ValueCategory = lvalue
+# 1110|         expr: b
+# 1110|             Type = unsigned int &
+# 1110|             ValueCategory = prvalue(load)
+# 1110|       2: (reference dereference)
+# 1110|           Type = unsigned int
+# 1110|           ValueCategory = lvalue
+# 1110|         expr: c
+# 1110|             Type = unsigned int &
+# 1110|             ValueCategory = prvalue(load)
+# 1110|       3: (reference dereference)
+# 1110|           Type = unsigned int
+# 1110|           ValueCategory = lvalue
+# 1110|         expr: d
+# 1110|             Type = unsigned int &
+# 1110|             ValueCategory = prvalue(load)
+# 1118|     1: return ...

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

@@ -1101,4 +1101,20 @@ int AsmStmt(int x) {
   return x;
 }
 
+static void AsmStmtWithOutputs(unsigned int& a, unsigned int& b, unsigned int& c, unsigned int& d)
+{
+#if defined(__GNUC__)
+  __asm__ __volatile__
+    (
+  "cpuid\n\t"
+    : "+a" (a), "+b" (b), "+c" (c), "+d" (d)
+    );
+#else
+  a++;
+  b++;
+  c++;
+  d++;
+#endif
+}
+
 // semmle-extractor-options: -std=c++17

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

@@ -5015,3 +5015,22 @@ ir.cpp:
 # 1099|     v0_11(void)       = ReturnValue              : &:r0_10, ~mu0_2
 # 1099|     v0_12(void)       = UnmodeledUse             : mu*
 # 1099|     v0_13(void)       = ExitFunction             : 
+
+# 1104| void AsmStmtWithOutputs(unsigned int&, unsigned int&, unsigned int&, unsigned int&)
+# 1104|   Block 0
+# 1104|     v0_0(void)                  = EnterFunction          : 
+# 1104|     mu0_1(unknown)              = AliasedDefinition      : 
+# 1104|     mu0_2(unknown)              = UnmodeledDefinition    : 
+# 1104|     r0_3(glval<unsigned int &>) = VariableAddress[a]     : 
+# 1104|     mu0_4(unsigned int &)       = InitializeParameter[a] : &:r0_3
+# 1104|     r0_5(glval<unsigned int &>) = VariableAddress[b]     : 
+# 1104|     mu0_6(unsigned int &)       = InitializeParameter[b] : &:r0_5
+# 1104|     r0_7(glval<unsigned int &>) = VariableAddress[c]     : 
+# 1104|     mu0_8(unsigned int &)       = InitializeParameter[c] : &:r0_7
+# 1104|     r0_9(glval<unsigned int &>) = VariableAddress[d]     : 
+# 1104|     mu0_10(unsigned int &)      = InitializeParameter[d] : &:r0_9
+# 1107|     mu0_11(unknown)             = InlineAsm              : ~mu0_2
+# 1118|     v0_12(void)                 = NoOp                   : 
+# 1104|     v0_13(void)                 = ReturnVoid             : 
+# 1104|     v0_14(void)                 = UnmodeledUse           : mu*
+# 1104|     v0_15(void)                 = ExitFunction           :