[WebAssembly] Distinguish symbol/debug names for functions and test

[ncw]

Summary

Previously, the function's "name" was sometimes mangled, sometimes not. Now we have a clear differentiation between symbol names and debug names.

Also adds support for --print-gc-sections for synthetic functions, so that the tests can be extended to cover the function names and debug names separately.

[sbc100]

lgtm, but maybe fix the names first.

test/wasm/undefined-weak-call.ll

16

Is this really what the stubs are called? I think we should at least make them valid C identifiers. __undefined_xxx?

[ncw]

test/wasm/undefined-weak-call.ll

16

In the symbol table, the stubs would have the original name. In the "name" section they have this pretty format.

Your suggested prefixed C identifier would only appear in this one single place... We could do it, it might be cleaner, but I've just played around with a couple of options and they're somewhat inelegant.

We basically want to differentiate between an InputFunction's identifier, and the "name" it has as a WasmFunction (which is demangled). We haven't needed that distinction until now.

I was actually thinking of putting the boot on the other foot: really, the -print-gc-sections log messages should be demangled for all symbols, don't you think? That would be another way to regain consistency.

[ncw]

Updated, with clear differentiation between (symbol) name and debug name.

Requires corresponding LLVM commit D45021

test/wasm/undefined-weak-call.ll

 ; RUN: llc -filetype=obj %s -o %t.o
-; RUN: wasm-ld --check-signatures --no-entry %t.o -o %t.wasm
+; RUN: wasm-ld --check-signatures --no-entry --print-gc-sections %t.o \
+; RUN:     -o %t.wasm 2>&1 | FileCheck -check-prefix=CHECK-GC %s
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 ; Check that calling an undefined weak function generates an appropriate stub
 ; that will fail at runtime with "unreachable".
 
 target triple = "wasm32-unknown-unknown-wasm"
 
 declare extern_weak void @weakFunc1()
 declare extern_weak void @weakFunc2()         ; same signature
 declare extern_weak void @weakFunc3(i32 %arg) ; different
 declare extern_weak void @weakFunc4()         ; should be GC'd as not called
 
+; CHECK-GC: removing unused section {{.*}}:(undefined function weakFunc4)
+
 define i32 @callWeakFuncs() {
   call void @weakFunc1()
   call void @weakFunc2()
   call void @weakFunc3(i32 2)
   %addr1 = ptrtoint void ()* @weakFunc1 to i32
   %addr4 = ptrtoint void ()* @weakFunc4 to i32
   %sum = add i32 %addr1, %addr4
   ret i32 %sum

wasm/MarkLive.cpp

if (Config->PrintGcSections) {
     for (const ObjFile *Obj : Symtab->ObjectFiles) {
       for (InputChunk *C : Obj->Functions)
         if (!C->Live)
           message("removing unused section " + toString(C));
       for (InputChunk *C : Obj->Segments)
         if (!C->Live)
           message("removing unused section " + toString(C));
     }
+    for (InputChunk *C : Symtab->SyntheticFunctions)
+      if (!C->Live)
+        message("removing unused section " + toString(C));
   }
 }