[llgo] set debuglocs for calls in synthetic functions

[axw]

Summary

Synthesized functions do not have valid locations,
and so we were not setting a debug location. Recent
changes to DI require that function call instructions
within a function having DI must have a location set.
We just set the debug location to line=0, col=0.

[pcc]

LGTM

[meadori]

Would someone mind committing this?
(I am happy to do so myself if no one has the cycles.)

With this patch, D27441, and D27442 llgo builds on trunk again.

debug/debug.go

 
 // Value creates an llvm.dbg.value call for the specified register value.
 func (d *DIBuilder) Value(b llvm.Builder, v ssa.Value, llv llvm.Value, paramIndex int) {
   // TODO(axw)
 }
 
 // SetLocation sets the current debug location.
 func (d *DIBuilder) SetLocation(b llvm.Builder, pos token.Pos) {
-  if !pos.IsValid() {
-    return
-  }
   position := d.fset.Position(pos)
   d.lb = llvm.Metadata{}
   if position.Filename != d.fnFile && position.Filename != "" {
     // This can happen rarely, e.g. in init functions.
     diFile := d.builder.CreateFile(d.remapFilePath(position.Filename), "")
     d.lb = d.builder.CreateLexicalBlockFile(d.scope(), diFile, 0)
   }
   b.SetCurrentDebugLocation(uint(position.Line), uint(position.Column), d.scope(), llvm.Metadata{})

irgen/ssa.go

if u.DumpSSA {
     f.WriteTo(os.Stderr)
   }
 
   fr := newFrame(u, llfn)
   defer fr.dispose()
   fr.addCommonFunctionAttrs(fr.function)
   fr.function.SetLinkage(linkage)
 
-  fr.logf("Define function: %s", f.String())
+  fr.logf("Define function: %s @ %s", f.String(), fr.pkg.Prog.Fset.Position(f.Pos()))
   fti := u.llvmtypes.getSignatureInfo(f.Signature)
   delete(u.undefinedFuncs, f)
   fr.retInf = fti.retInf
 
   // Push the compile unit and function onto the debug context.
   if u.GenerateDebug {
     u.debug.PushFunction(fr.function, f.Signature, f.Pos())
     defer u.debug.PopFunction()