fix spurious error when a global var is removed

IPO issues must be skipable so alivecc can find the real issues

Author: nunoplopes

llvm_util/llvm2alive.cpp

@@ -1617,15 +1617,10 @@ class llvm2alive_ : public llvm::InstVisitor<llvm2alive_, unique_ptr<Instr>> {
     auto &entry_name = Fn.getFirstBB().getName();
     BB = &Fn.getBB("#init", true);
 
+    // Ensure all src globals exist in target as well
     for (auto &gvname : gvnamesInSrc) {
-      auto gv = getGlobalVariable(string(gvname));
-      if (!gv) {
-        // global variable removed or renamed
-        *out << "ERROR: Unsupported interprocedural transformation\n";
-        return {};
-      }
-      // If gvname already exists in tgt, get_operand will immediately return
-      get_operand(gv);
+      if (auto gv = getGlobalVariable(string(gvname)))
+        get_operand(gv);
     }
 
     map<string, unique_ptr<Store>> stores;

tests/alive-tv/memory/remove-global.src.ll

@@ -0,0 +1,8 @@
+; ERROR: Mismatch in memory
+
+@glb = internal global i8 0
+
+define void @f() {
+  store i8 0, ptr @glb
+  ret void
+}

tests/alive-tv/memory/remove-global.tgt.ll

@@ -0,0 +1,3 @@
+define void @f() {
+  ret void
+}

tests/clang-tv/skip-globalopt.c

@@ -0,0 +1,7 @@
+// TEST-ARGS: -O2
+
+static int x;
+
+void fn() {
+  x = 0;
+}