From e0cfbb53dc74a1d283bd39fef13f8731c9dac326 Mon Sep 17 00:00:00 2001
From: Robert Marsh <rdmarsh@semmle.com>
Date: Mon, 1 Aug 2022 09:52:46 -0400
Subject: [PATCH] C++: add missing SideEffectElimination.qll

---
 .../internal/SideEffectElimination.qll        | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 cpp/ql/lib/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SideEffectElimination.qll

diff --git a/cpp/ql/lib/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SideEffectElimination.qll b/cpp/ql/lib/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SideEffectElimination.qll
new file mode 100644
index 00000000000..b5aa5134b47
--- /dev/null
+++ b/cpp/ql/lib/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SideEffectElimination.qll
@@ -0,0 +1,42 @@
+import cpp as CPP
+import semmle.code.cpp.ir.implementation.unaliased_ssa.IR as Unaliased
+import AliasAnalysis as Alias
+import AliasConfiguration as Conf
+import semmle.code.cpp.models.interfaces.SideEffect as SideEffect
+
+private predicate noLocalSideEffectWrite(CPP::Function func) {
+  forall(Unaliased::AddressOperand addr | addr.getUse().getEnclosingFunction() = func |
+    not (
+      Alias::getAddressOperandAllocation(addr) instanceof Conf::VariableAllocation and
+      Alias::getAddressOperandAllocation(addr).(Conf::VariableAllocation).alwaysEscapes()
+    )
+  )
+}
+
+language[monotonicAggregates]
+private predicate noTransitiveSideEffectWrite(CPP::Function func) {
+  exists(Unaliased::IRFunction irFunc | irFunc.getFunction() = func) and
+  noLocalSideEffectWrite(func) and
+  forall(Unaliased::CallInstruction call | call.getEnclosingFunction() = func |
+    exists(call.getStaticCallTarget())
+  ) and
+  forall(Unaliased::CallInstruction call, CPP::Function callee |
+    call.getStaticCallTarget() = callee and
+    call.getEnclosingFunction() = func
+  |
+    noTransitiveSideEffectWrite(callee)
+    or
+    callee.(SideEffect::SideEffectFunction).hasOnlySpecificWriteSideEffects()
+  )
+}
+
+predicate removeableSideEffect(Unaliased::SideEffectInstruction instr) {
+  (
+    instr instanceof Unaliased::CallSideEffectInstruction or
+    instr instanceof Unaliased::CallReadSideEffectInstruction
+  ) and
+  noTransitiveSideEffectWrite(instr
+        .getPrimaryInstruction()
+        .(Unaliased::CallInstruction)
+        .getStaticCallTarget())
+}