Translate only the taken branch of constant if conditions

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -1382,13 +1382,15 @@ bool Converter::VisitIfStmt(clang::IfStmt *stmt) {
     stmt->setInit(init);
     return false;
   }
-  StrCat(keyword::kIf);
-  if (auto *cond = clang::dyn_cast<clang::ConstantExpr>(stmt->getCond());
-      cond && stmt->isConstexpr()) {
-    StrCat(cond->getResultAsAPSInt() != 0 ? keyword::kTrue : keyword::kFalse);
-  } else {
-    ConvertCondition(stmt->getCond());
+  if (bool taken = false;
+      !stmt->getConditionVariable() && !stmt->isConsteval() &&
+      !stmt->getCond()->isValueDependent() &&
+      stmt->getCond()->EvaluateAsBooleanCondition(taken, ctx_)) {
+    ConvertBody(taken ? stmt->getThen() : stmt->getElse());
+    return false;
   }
+  StrCat(keyword::kIf);
+  ConvertCondition(stmt->getCond());
   ConvertBody(stmt->getThen());
   if (stmt->hasElseStorage()) {
     StrCat(keyword::kElse);

tests/unit/if_constexpr.cpp

@@ -18,11 +18,22 @@ int keep_both(int x) {
   }
 }
 
+template <typename T> unsigned long long widen(T v) {
+  if (sizeof(T) > 4) {
+    T hi = v;
+    hi <<= 32;
+    return hi;
+  }
+  return v;
+}
+
 int main() {
   int v = 7;
   assert(classify(&v) == 7);
   assert(classify(1L) == 2);
   assert(classify(1) == 1);
   assert(keep_both(1) == 2);
+  assert(widen(1u) == 1);
+  assert(widen(1ull) == 4294967296ull);
   return 0;
 }