[TableGen] defm in a loop is not final (bug fix)

[hfinkel]

Summary

The TableGen parsing code has a bug: when parsing a defm statement, it tries to do a final resolution even if inside a top-level loop. This doesn't work, however, if things inside the multiclass being resolved need access to the loop-iteration variable. These defm statements need to be delayed until the top-level loop itself is evaluated.

As a quick example, given this:

multiclass D<bit b> {
  def A;

  foreach _ = !if(b, [0], []<int>) in
  def B;
}

foreach ShouldI = 0-1 in
defm MD#ShouldI : D<ShouldI>;

TableGen would provide a parsing error:

foreach-multiclass.td:93:3: error: attempting to loop over '!if(ShouldI, [0], [])', expected a list
  foreach _ = !if(b, [0], []<int>) in
  ^

When the defm resolution is delayed, the evaluation works as expected.

[simon_tatham]

llvm/test/TableGen/foreach-multiclass.td

98

Of course, we've got a proper if statement now! I wonder if it's worth checking that this construction works with that as well as with the foreach dodge?

(It should, because if I remember, if expands to that anyway under the hood. But just in case the implementation changes in future, perhaps.)

[hfinkel]

llvm/test/TableGen/foreach-multiclass.td

98

Yep. In real life, I'm using it with the if statement. Because if expands to this, I put it in the test this way (because this is the foreach-multiclass test, and to make it clearer how the test corresponded to the fix). Would you prefer that I also explicitly add a test with an if statement?

[simon_tatham]

llvm/test/TableGen/foreach-multiclass.td

98

That would be my preference, just because the implementation of if by foreach seemed like the kind of shortcut I wouldn't bet on staying true for ever.

llvm/lib/TableGen/TGParser.cpp

for (unsigned i = 0, e = TArgs.size(); i != e; ++i) {
                            "'");
         }
         Substs.emplace_back(TArgs[i], Default);
       }
     }
 
     Substs.emplace_back(QualifiedNameOfImplicitName(MC), DefmName);
 
-    if (resolve(MC->Entries, Substs, CurMultiClass == nullptr, &NewEntries,
-                &SubClassLoc))
+    if (resolve(MC->Entries, Substs, CurMultiClass == nullptr && Loops.empty(),
+                &NewEntries, &SubClassLoc))
       return true;
 
     if (!consume(tgtok::comma))
       break;
 
     if (Lex.getCode() != tgtok::Id)
       return TokError("expected identifier");
 

llvm/test/TableGen/foreach-multiclass.td

 // CHECK-NOT: def F1
 // CHECK-NOT: def F2_0_0
 // CHECK:     def F2_1_0
 // CHECK-NOT: def F2_1_2
 // CHECK:     def F2_2_0
 // CHECK:     def F2_2_1
 // CHECK-NOT: def F2_2_2
 
+// CHECK:     def MD0A
+// CHECK-NOT: def MD0B
+// CHECK:     def MD1A
+// CHECK:     def MD1B
+
 multiclass A<int x> {
   foreach i = [0, 1] in {
     def NAME#i {
       int sum = !add(x, i);
     }
   }
 }
 
multiclass C<int x> {
   }
 }
 
 defm C0 : C<4>;
 
 multiclass D<bit b> {
   def A;
 
   foreach _ = !if(b, [0], []<int>) in
   def B;
 }
 
 defm D0 : D<0>;
 defm D1 : D<1>;
 
 multiclass E<list<int> lst, int x>
   : C<x> {
multiclass F<list<int> lst> {
   foreach j = !foldl([]<int>, lst, lhs, x,
                      !if(!lt(x, i), !listconcat(lhs, [x]), lhs)) in
   def _#i#_#j;
 }
 
 defm F0 : F<[]>;
 defm F1 : F<[0]>;
 defm F2 : F<[0, 1, 2]>;
+
+foreach ShouldI = 0-1 in
+defm MD#ShouldI : D<ShouldI>;
+