avoid warnings by the C compiler on unused local variables

titan-lang · Oct 20, 2017 · eedd59a · eedd59a
1 parent 347edf8
commit eedd59a
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Showing 3 changed files with 45 additions and 22 deletions.
diff --git a/spec/coder_spec.lua b/spec/coder_spec.lua
@@ -420,9 +420,25 @@ describe("Titan code generator ", function()
         local ok, err = checker.check(ast, code, "test.titan")
         assert.truthy(ok, err)
         assert.same("Exp_ToInt", ast[1].block.stats[2].exp._tag)
-        local ok, err = generate(ast, "titan_test1")
+        local ok, err = generate(ast, "titan_test")
+        assert.truthy(ok, err)
+        local ok, err = call("titan_test", "local x = titan_test.fn(); assert(math.type(x) == 'integer')")
         assert.truthy(ok, err)
-        local ok, err = call("titan_test1", "local x = titan_test1.fn(); assert(math.type(x) == 'integer')")
+    end)
+
+    it("handles unused locals", function()
+        local code = [[
+            function fn(): nil
+                local f: float = 1.0
+                local i: integer = f
+            end
+        ]]
+        local ast, err = parser.parse(code)
+        assert.truthy(ast, err)
+        local ok, err = checker.check(ast, code, "test.titan")
+        assert.truthy(ok, err)
+        assert.same("Exp_ToInt", ast[1].block.stats[2].exp._tag)
+        local ok, err = generate(ast, "titan_test")
         assert.truthy(ok, err)
     end)
 

diff --git a/titan-compiler/checker.lua b/titan-compiler/checker.lua
@@ -324,14 +324,14 @@ function checkexp(node, st, errors, context)
     if tag == "Var_Name" then
         local decl = st:find_symbol(node.name)
         if not decl then
-            -- TODO generate better error messages when we have the line num
             local msg = "variable '" .. node.name .. "' not declared"
             typeerror(errors, msg, node._pos)
             node._type = types.Integer
         elseif decl._tag == "TopLevel_Func" then
             typeerror(errors, "reference to function " .. node.name .. " outside of function call", decl._pos)
             node._type = types.Integer
         else
+            decl._used = true
             node._decl = decl
             node._type = decl._type
         end

diff --git a/titan-compiler/coder.lua b/titan-compiler/coder.lua
@@ -434,28 +434,35 @@ function codestat(ctx, node)
     local tag = node._tag
     if tag == "Stat_Decl" then
         local cstats, cexp = codeexp(ctx, node.exp)
-        local typ = node.decl._type
-        node.decl._cvar = "_local_" .. node.decl.name
-        local cdecl = ctype(typ) .. " " .. node.decl._cvar .. ";"
-        local cslot = ""
-        local cset = ""
-        if types.is_gc(typ) then
-            node.decl._slot = "_localslot_" .. node.decl.name
-            cslot = newslot(ctx, node.decl._slot);
-            cset = string.format([[
-                /* update slot */
+        if node.decl._used then
+            local typ = node.decl._type
+            node.decl._cvar = "_local_" .. node.decl.name
+            local cdecl = ctype(typ) .. " " .. node.decl._cvar .. ";"
+            local cslot = ""
+            local cset = ""
+            if types.is_gc(typ) then
+                node.decl._slot = "_localslot_" .. node.decl.name
+                cslot = newslot(ctx, node.decl._slot);
+                cset = string.format([[
+                    /* update slot */
+                    %s
+                ]], setslot(typ, node.decl._slot, node.decl._cvar))
+            end
+            return string.format([[
                 %s
-            ]], setslot(typ, node.decl._slot, node.decl._cvar))
-        end
-        return string.format([[
-            %s
-            %s
-            {
                 %s
-                %s = %s;
+                {
+                    %s
+                    %s = %s;
+                    %s
+                }
+            ]], cdecl, cslot, cstats, node.decl._cvar, cexp, cset)
+        else
+            return string.format([[
                 %s
-            }
-        ]], cdecl, cslot, cstats, node.decl._cvar, cexp, cset)
+                ((void)%s);
+            ]], cstats, cexp)
+        end
     elseif tag == "Stat_Block" then
         return codeblock(ctx, node)
     elseif tag == "Stat_While" then