wasm: only export explicitly exported functions

Previously we used the --export-all linker flag to export most
functions. However, this is not needed and possibly increases binary
size. Instead, we should be exporting the specific functions to be
exported.

compiler/compiler.go

@@ -23,7 +23,7 @@ import (
 // Version of the compiler pacakge. Must be incremented each time the compiler
 // package changes in a way that affects the generated LLVM module.
 // This version is independent of the TinyGo version number.
-const Version = 1
+const Version = 2 // last change: adding wasm-export-name attribute
 
 func init() {
 	llvm.InitializeAllTargets()
@@ -781,6 +781,12 @@ func (b *builder) createFunction() {
 		b.llvmFn.SetVisibility(llvm.HiddenVisibility)
 		b.llvmFn.SetUnnamedAddr(true)
 	}
+	if b.info.exported && strings.HasPrefix(b.Triple, "wasm") {
+		// Set the exported name. This is necessary for WebAssembly because
+		// otherwise the function is not exported.
+		functionAttr := b.ctx.CreateStringAttribute("wasm-export-name", b.info.linkName)
+		b.llvmFn.AddFunctionAttr(functionAttr)
+	}
 
 	// Some functions have a pragma controlling the inlining level.
 	switch b.info.inline {

targets/wasm.json

@@ -14,7 +14,6 @@
 	"ldflags": [
 		"--allow-undefined",
 		"--stack-first",
-		"--export-all",
 		"--no-demangle"
 	],
 	"emulator":      ["node", "targets/wasm_exec.js"],