[WebAssembly] Basic support for Wasm object file encoding.

With the "wasm32-unknown-unknown-wasm" triple, this allows writing out
simple wasm object files, and is another step in a larger series toward
migrating from ELF to general wasm object support. Note that this code
and the binary format itself is still experimental.

llvm-svn: 296190

1 files changed, 13 insertions, 3 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 0651a1c11b4..04bf7b118b7 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -85,6 +85,14 @@ WebAssemblyTargetMachine::WebAssemblyTargetMachine(
   // 'unreachable' instructions which is meant for that case.
   this->Options.TrapUnreachable = true;
 
+  // WebAssembly treats each function as an independent unit. Force
+  // -ffunction-sections, effectively, so that we can emit them independently.
+  if (!TT.isOSBinFormatELF()) {
+    this->Options.FunctionSections = true;
+    this->Options.DataSections = true;
+    this->Options.UniqueSectionNames = true;
+  }
+
   initAsmInfo();
 
   // Note that we don't use setRequiresStructuredCFG(true). It disables
@@ -264,12 +272,14 @@ void WebAssemblyPassConfig::addPreEmitPass() {
     addPass(createWebAssemblyRegColoring());
   }
 
+  // Eliminate multiple-entry loops. Do this before inserting explicit get_local
+  // and set_local operators because we create a new variable that we want
+  // converted into a local.
+  addPass(createWebAssemblyFixIrreducibleControlFlow());
+
   // Insert explicit get_local and set_local operators.
   addPass(createWebAssemblyExplicitLocals());
 
-  // Eliminate multiple-entry loops.
-  addPass(createWebAssemblyFixIrreducibleControlFlow());
-
   // Put the CFG in structured form; insert BLOCK and LOOP markers.
   addPass(createWebAssemblyCFGStackify());