fix #7836, speed bump due to unreachable code

Author: JeffBezanson

base/inference.jl

@@ -1681,7 +1681,10 @@ function type_annotate(ast::Expr, states::Array{Any,1}, sv::ANY, rettype::ANY,
     body = ast.args[3].args::Array{Any,1}
     for i=1:length(body)
         st_i = states[i]
-        body[i] = eval_annotate(body[i], (st_i === () ? emptydict : st_i), sv, decls, closures)
+        if st_i !== ()
+            # st_i === ()  =>  unreached statement  (see issue #7836)
+            body[i] = eval_annotate(body[i], st_i, sv, decls, closures)
+        end
     end
     ast.args[3].typ = rettype
 

src/codegen.cpp

@@ -2362,15 +2362,20 @@ static Value *var_binding_pointer(jl_sym_t *s, jl_binding_t **pbnd,
 static Value *emit_checked_var(Value *bp, jl_sym_t *name, jl_codectx_t *ctx)
 {
     Value *v = tpropagate(bp, builder.CreateLoad(bp, false));
-    Value *ok = builder.CreateICmpNE(v, V_null);
-    BasicBlock *err = BasicBlock::Create(getGlobalContext(), "err", ctx->f);
-    BasicBlock *ifok = BasicBlock::Create(getGlobalContext(), "ok");
-    builder.CreateCondBr(ok, ifok, err);
-    builder.SetInsertPoint(err);
-    builder.CreateCall(prepare_call(jlundefvarerror_func), literal_pointer_val((jl_value_t*)name));
-    builder.CreateBr(ifok);
-    ctx->f->getBasicBlockList().push_back(ifok);
-    builder.SetInsertPoint(ifok);
+    // in unreachable code, there might be a poorly-typed instance of a variable
+    // that has a concrete type everywhere it's actually used. tolerate this
+    // situation by just skipping the NULL check if it wouldn't be valid. (issue #7836)
+    if (v->getType() == jl_pvalue_llvmt) {
+        Value *ok = builder.CreateICmpNE(v, V_null);
+        BasicBlock *err = BasicBlock::Create(getGlobalContext(), "err", ctx->f);
+        BasicBlock *ifok = BasicBlock::Create(getGlobalContext(), "ok");
+        builder.CreateCondBr(ok, ifok, err);
+        builder.SetInsertPoint(err);
+        builder.CreateCall(prepare_call(jlundefvarerror_func), literal_pointer_val((jl_value_t*)name));
+        builder.CreateBr(ifok);
+        ctx->f->getBasicBlockList().push_back(ifok);
+        builder.SetInsertPoint(ifok);
+    }
     return v;
 }