builder: add support for -opt=0

This optimization level wasn't working before because some passes expect
some globals to be cleaned up afterwards. Cleaning these globals is
easy, just add the pass necessary for it. This shouldn't reduce the
usefulness of the -opt=0 build flag as most optimizations are still
skipped.

Makefile

@@ -391,6 +391,8 @@ endif
 	@$(MD5SUM) test.hex
 	$(TINYGO) build             -o test.nro -target=nintendoswitch      examples/serial
 	@$(MD5SUM) test.nro
+	$(TINYGO) build -size short -o test.hex -target=pca10040 -opt=0     ./testdata/stdlib.go
+	@$(MD5SUM) test.hex
 
 wasmtest:
 	$(GO) test ./tests/wasm

builder/build.go

@@ -411,15 +411,8 @@ func compileWholeProgram(pkgName string, config *compileopts.Config, compilerCon
 	// exactly.
 	errs = nil
 	switch config.Options.Opt {
-	/*
-		Currently, turning optimizations off causes compile failures.
-		We rely on the optimizer removing some dead symbols.
-		Avoid providing an option that does not work right now.
-		In the future once everything has been fixed we can re-enable this.
-
-		case "none", "0":
-			errs = transform.Optimize(mod, config, 0, 0, 0) // -O0
-	*/
+	case "none", "0":
+		errs = transform.Optimize(mod, config, 0, 0, 0) // -O0
 	case "1":
 		errs = transform.Optimize(mod, config, 1, 0, 0) // -O1
 	case "2":

transform/optimizer.go

@@ -111,6 +111,12 @@ func Optimize(mod llvm.Module, config *compileopts.Config, optLevel, sizeLevel i
 		if len(errs) > 0 {
 			return errs
 		}
+
+		// Clean up some leftover symbols of the previous transformations.
+		goPasses := llvm.NewPassManager()
+		defer goPasses.Dispose()
+		goPasses.AddGlobalDCEPass()
+		goPasses.Run(mod)
 	}
 
 	// Lower async implementations.