In inference, make string constants module local

During inference, we can end up in a situation where the stack looks like

COMPILE B
CALL B
COMPILE A
CALL A

If A and B are methods of the same functions, it is likely that they share
string constants, but in MCJIT these will be allocated in the module for A,
so when B references them, the call to B tries to materialize the modules for
both A and B, leading to an assertion failure, because the compile for A is
not finished yet. Work around this by disabling string constant pooling in
inference. The proper fix is to write an LLVM pass that records the location
of global constants before the module is emitted and merges them there.

src/cgutils.cpp

@@ -78,11 +78,18 @@ static inline void add_named_global(GlobalValue *gv, void *addr)
 // --- string constants ---
 static std::map<const std::string, GlobalVariable*> stringConstants;
 
+extern "C" {
+    extern int jl_in_inference;
+}
+
 static GlobalVariable *stringConst(const std::string &txt)
 {
     GlobalVariable *gv = stringConstants[txt];
     static int strno = 0;
-    if (gv == NULL) {
+    // in inference, we can not share string constants between
+    // modules as there might be multiple compiles on the stack
+    // with calls in between them.
+    if (gv == NULL || jl_in_inference) {
         std::stringstream ssno;
         std::string vname;
         ssno << strno;
@@ -102,6 +109,7 @@ static GlobalVariable *stringConst(const std::string &txt)
                                                        txt.length()+1)),
 #endif
                                 vname);
+        gv->setUnnamedAddr(true);
         stringConstants[txt] = gv;
         strno++;
     }

src/codegen.cpp

@@ -3520,9 +3520,15 @@ static void finalize_gc_frame(jl_codectx_t *ctx)
         Instruction *after = ctx->argSpaceInits;
 
         for(size_t i=0; i < (size_t)ctx->maxDepth; i++) {
+#ifdef LLVM37
+            Instruction *argTempi =
+                GetElementPtrInst::Create(NULL,newgcframe,
+                                          ConstantInt::get(T_int32, i+ctx->argSpaceOffs+2));
+#else
             Instruction *argTempi =
                 GetElementPtrInst::Create(newgcframe,
                                           ConstantInt::get(T_int32, i+ctx->argSpaceOffs+2));
+#endif
             instList.insertAfter(after, argTempi);
             after = new StoreInst(V_null, argTempi);
             instList.insertAfter(argTempi, after);