[AsmParser] Fix support for zero bit integer types.

[lattner]

Summary

Zero bit integer types are supported by IntegerType for consistency,
but the asmparser never got updated. Allow them to be parsed, as
required to fix CIRCT issue #316

[mehdi_amini]

It seems that we would accept to parse i032 in place of i32, is this intentional? Should we limit the 0 to i0 alone?

[lattner]

I can do that, but is there a reason to reject that?

[mehdi_amini]

I don't know :)
I just wanted to be sure this was intentional!
I'm fine with letting this through.

[lattner]

Thanks Mehdi!

mlir/lib/Parser/Token.cpp

Optional<double> Token::getFloatingPointValue() const {
   return result;
 }
 
 /// For an inttype token, return its bitwidth.
 Optional<unsigned> Token::getIntTypeBitwidth() const {
   assert(getKind() == inttype);
   unsigned bitwidthStart = (spelling[0] == 'i' ? 1 : 2);
   unsigned result = 0;
-  if (spelling[bitwidthStart] == '0' ||
-      spelling.drop_front(bitwidthStart).getAsInteger(10, result) ||
-      result == 0)
+  if (spelling.drop_front(bitwidthStart).getAsInteger(10, result))
     return None;
   return result;
 }
 
 Optional<bool> Token::getIntTypeSignedness() const {
   assert(getKind() == inttype);
   if (spelling[0] == 'i')
     return llvm::None;

mlir/test/Dialect/Quant/parse-any-invalid.mlir

 !qalias = type !quant.any<i33:f32>
 
 // -----
 // Unrecognized storage type: storage size < 0
 // expected-error@+1 {{illegal storage type size: 1024}}
 !qalias = type !quant.any<i1024<-4:3>:f32>
 
 // -----
-// Unrecognized storage type: storage size == 0
+// Unrecognized storage type: storage size
 // expected-error@+1 {{invalid integer width}}
-!qalias = type !quant.any<i0<-4:3>:f32>
+!qalias = type !quant.any<i0123123123123123<-4:3>:f32>
 
 // -----
 // Illegal storage min/max: max - min < 0
 // expected-error@+1 {{illegal storage min and storage max: (2:1)}}
 !qalias = type !quant.any<i8<2:1>:f32>
 
 // -----
 // Illegal storage min/max: max - min == 0

mlir/test/Dialect/Quant/parse-uniform-invalid.mlir

 !qalias = type !quant.uniform<i33:f32, 0.99872:127>
 
 // -----
 // Unrecognized storage type: storage size < 0
 // expected-error@+1 {{illegal storage type prefix}}
 !qalias = type !quant.uniform<i-1<-4:3>:f32, 0.99872:127>
 
 // -----
-// Unrecognized storage type: storage size == 0
+// Unrecognized storage type: storage size
 // expected-error@+1 {{invalid integer width}}
-!qalias = type !quant.uniform<i0<-4:3>:f32, 0.99872:127>
+!qalias = type !quant.uniform<i123123123120<-4:3>:f32, 0.99872:127>
 
 // -----
 // Illegal storage min/max: max - min < 0
 // expected-error@+1 {{illegal storage min and storage max: (2:1)}}
 !qalias = type !quant.uniform<i8<2:1>:f32, 0.99872:127>
 
 // -----
 // Illegal storage min/max: max - min == 0

mlir/test/IR/invalid.mlir

 ^bb40:
   "foo"() : ()->()
   ""() : ()->()  // expected-error {{empty operation name is invalid}}
   return
 }
 
 // -----
 
-func @illegaltype(i0) // expected-error {{invalid integer width}}
+func @illegaltype(i21312312323120) // expected-error {{invalid integer width}}
 
 // -----
 
 func @malformed_for_percent() {
   affine.for i = 1 to 10 { // expected-error {{expected SSA operand}}
 
 // -----
 

mlir/test/IR/parser.mlir

 func private @bar() -> ()
 
 // CHECK: func private @baz() -> (i1, index, f32)
 func private @baz() -> (i1, index, f32)
 
 // CHECK: func private @missingReturn()
 func private @missingReturn()
 
-// CHECK: func private @int_types(i1, i2, i4, i7, i87) -> (i1, index, i19)
-func private @int_types(i1, i2, i4, i7, i87) -> (i1, index, i19)
+// CHECK: func private @int_types(i0, i1, i2, i4, i7, i87) -> (i1, index, i19)
+func private @int_types(i0, i1, i2, i4, i7, i87) -> (i1, index, i19)
 
 // CHECK: func private @sint_types(si2, si4) -> (si7, si1023)
 func private @sint_types(si2, si4) -> (si7, si1023)
 
 // CHECK: func private @uint_types(ui2, ui4) -> (ui7, ui1023)
 func private @uint_types(ui2, ui4) -> (ui7, ui1023)