From 3aa0189bfe3606c48af75cde04562f29273dfbcc Mon Sep 17 00:00:00 2001
From: JF Bastien <jfb@google.com>
Date: Wed, 21 Oct 2015 02:23:09 +0000
Subject: [PATCH] WebAssembly: support imports

C/C++ code can declare an extern function, which will show up as an import in WebAssembly's output. It's expected that the linker will resolve these, and mark unresolved imports as call_import (I have a patch which does this in wasmate).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250875 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../WebAssembly/WebAssemblyAsmPrinter.cpp     | 24 ++++++++++++++++++-
 test/CodeGen/WebAssembly/import.ll            | 21 ++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 test/CodeGen/WebAssembly/import.ll

diff --git a/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index e20ee695e6f..f3e3170dad2 100644
--- a/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -77,8 +77,8 @@ private:
   void EmitJumpTableInfo() override;
   void EmitConstantPool() override;
   void EmitFunctionBodyStart() override;
-
   void EmitInstruction(const MachineInstr *MI) override;
+  void EmitEndOfAsmFile(Module &M) override;
 
   std::string getRegTypeName(unsigned RegNo) const;
   static std::string toString(const APFloat &APF);
@@ -330,6 +330,28 @@ void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   }
 }
 
+void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
+    SmallString<128> Str;
+    raw_svector_ostream OS(Str);
+  for (const Function &F : M)
+    if (F.isDeclarationForLinker()) {
+      assert(F.hasName() && "imported functions must have a name");
+      if (F.getName().startswith("llvm."))
+	continue;
+      if (Str.empty())
+	OS << "\t.imports\n";
+      Type *Rt = F.getReturnType();
+      OS << "\t.import " <<  toSymbol(F.getName()) << " \"\" \"" << F.getName()
+	 << "\"";
+      for (const Argument &A : F.args())
+	OS << " (param " << toString(A.getType()) << ')';
+      if (!Rt->isVoidTy())
+	OS << " (result " << toString(Rt) << ')';
+      OS << '\n';
+  }
+  OutStreamer->EmitRawText(OS.str());
+}
+
 // Force static initialization.
 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(TheWebAssemblyTarget32);
diff --git a/test/CodeGen/WebAssembly/import.ll b/test/CodeGen/WebAssembly/import.ll
new file mode 100644
index 00000000000..d1dca7fa8bb
--- /dev/null
+++ b/test/CodeGen/WebAssembly/import.ll
@@ -0,0 +1,21 @@
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
+
+target datalayout = "e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+; CHECK-LABEL: .text
+; CHECK-LABEL: f:
+define void @f(i32 %a, float %b) {
+  tail call i32 @printi(i32 %a)
+  tail call float @printf(float %b)
+  tail call void @printv()
+  ret void
+}
+
+; CHECK-LABEL: .imports
+; CHECK-NEXT:  .import $printi "" "printi" (param i32) (result i32)
+; CHECK-NEXT:  .import $printf "" "printf" (param f32) (result f32)
+; CHECK-NEXT:  .import $printv "" "printv"
+declare i32 @printi(i32)
+declare float @printf(float)
+declare void @printv()
-- 
2.34.1