fix #1107: false positive with const removal

Author: nunoplopes

ir/memory.cpp

@@ -2575,12 +2575,8 @@ Memory::refined(const Memory &other, bool fncall,
     if (p.isByval().isTrue() && q.isByval().isTrue())
       continue;
 
-    // In assembly mode we verify each function individually and
-    // global constants are not validated (assumed to be correct).
-    // Hence we may not have all initializers if tgt doesn't reference them.
-    if (other.isAsmMode() &&
-        is_constglb(bid) &&
-        isInitialMemBlock(other.non_local_block_val[bid].val, false))
+    // Constants that are not referenced can be removed.
+    if (is_constglb(bid) && !other.state->isGVUsed(bid))
       continue;
 
     ret &= (ptr_bid == bid_expr).implies(blockRefined(p, q, bid, undef_vars));

ir/state.cpp

@@ -1392,13 +1392,22 @@ void State::markGlobalAsAllocated(const string &glbvar) {
   itr->second.second = true;
 }
 
+bool State::isGVUsed(unsigned bid) const {
+  for (auto &[gv_name, data] : glbvar_bids) {
+    if (bid == data.first)
+      return getFn().getUsers().count(getFn().getGlobalVar(gv_name));
+  }
+  assert(false);
+  return false;
+}
+
 void State::syncSEdataWithSrc(State &src) {
   assert(glbvar_bids.empty());
   assert(src.isSource() && !isSource());
   glbvar_bids = src.glbvar_bids;
-  for (auto &itm : glbvar_bids)
-    itm.second.second = false;
-
+  for (auto &[gv_name, data] : glbvar_bids) {
+    data.second = false;
+  }
   fn_call_data = std::move(src.fn_call_data);
   inaccessiblemem_bids = std::move(src.inaccessiblemem_bids);
   memory.syncWithSrc(src.returnMemory());

ir/state.h

@@ -363,6 +363,7 @@ class State {
   bool hasGlobalVarBid(const std::string &glbvar, unsigned &bid,
                        bool &allocated) const;
   void markGlobalAsAllocated(const std::string &glbvar);
+  bool isGVUsed(unsigned bid) const;
   void syncSEdataWithSrc(State &src);
 
   void mkAxioms(State &tgt);

tests/alive-tv/memory/const-removal.src.ll

@@ -0,0 +1,11 @@
+; this test must use separate files
+
+@x = private constant i32 1
+
+define i32 @f() {
+  ret i32 0
+
+dead:    
+  call void null(ptr @x)
+  unreachable
+}

tests/alive-tv/memory/const-removal.tgt.ll

@@ -0,0 +1,3 @@
+define i32 @f() {
+  ret i32 0
+}