[WebAssembly] Make sret parameter work with AddMissingPrototypes

[aheejin]

Summary

Even with functions with no-prototype attribute, there can be an
argument sret (structure return) attribute, which is an optimization
when a function return type is a struct. Fixes PR42420.

[aheejin]

• Comment fix

[sbc100]

lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp

83

Is there some kind of "any" construct in llvm that could take A.hasStructRetAttr as a predicate?

[aheejin]

• Use llvm::any_of

[aheejin]

lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp

83

It does not seem to be possible to use hasStructRetAttr directly as an argument to llvm:any_of without some more binding functions, in which case I think it might be overly complicated. So I used a named lambda instead. (Unnamed lambda makes indentation kind of ugly here)

[sbc100]

lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp

83

No worries. I was mostly just curious. lgtm either way.

[aheejin]

• sret argument should be the first one

lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp

83

Come to think of it, there can be at most one argument in this case and that should be the sret argument. Maybe we don't need a loop or any_of.

lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp

for (Function &F : M) {
 
     // When clang emits prototype-less C functions it uses (...), i.e. varargs
     // function that take no arguments (have no sentinel).  When we see a
     // no-prototype attribute we expect the function have these properties.
     if (!F.isVarArg())
       report_fatal_error(
           "Functions with 'no-prototype' attribute must take varargs: " +
           F.getName());
-    if (F.getFunctionType()->getNumParams() != 0)
-      report_fatal_error(
-          "Functions with 'no-prototype' attribute should not have params: " +
+    if (F.getFunctionType()->getNumParams() != 0) {
+      for (Argument &A : F.args())
+        if (!A.hasStructRetAttr())
+          report_fatal_error("Functions with 'no-prototype' attribute should "
+                             "not have params: " +
                              F.getName());
+    }
 
     // Create a function prototype based on the first call site (first bitcast)
     // that we find.
     FunctionType *NewType = nullptr;
     for (Use &U : F.uses()) {
       LLVM_DEBUG(dbgs() << "prototype-less use: " << F.getName() << "\n");
       LLVM_DEBUG(dbgs() << *U.getUser() << "\n");
       if (auto *BC = dyn_cast<BitCastOperator>(U.getUser())) {

test/CodeGen/WebAssembly/add-prototypes.ll

 
 ; CHECK-LABEL: @as_paramater
 ; CHECK: call void @func_param(i64 (...)* bitcast (i64 (i32)* @foo to i64 (...)*))
 define void @as_paramater() {
   call void @func_param(i64 (...)* @foo)
   ret void
 }
 
+; Check if a sret parameter works with no-prototype function.
+; CHECK-LABEL: @sret_param
+; CHECK: call void @make_struct_foo(%struct.foo* sret %foo)
+%struct.foo = type { i32, i32 }
+declare void @make_struct_foo(%struct.foo* sret, ...) #1
+define void @sret_param() {
+  %foo = alloca %struct.foo, align 4
+  call void bitcast (void (%struct.foo*, ...)* @make_struct_foo to void (%struct.foo*)*)(%struct.foo* sret %foo)
+  ret void
+}
+
 declare void @func_param(i64 (...)*)
 
 ; CHECK: declare void @func_not_called()
 declare void @func_not_called(...) #1
 
 ; CHECK: declare extern_weak i64 @foo(i32)
 declare extern_weak i64 @foo(...) #1
 
 ; CHECK-NOT: attributes {{.*}} = { {{.*}}"no-prototype"{{.*}} }
 attributes #1 = { "no-prototype" }