cmd/compile: fix generic inter-inter comparisons from value switch st…

…atements

If value is a non-empty interface and has shape, we still need to
convert it to an interface{} first.

Fixes golang#53477

Change-Id: I516063ba4429a6cc24c483758387ec13815fc63e
Reviewed-on: https://go-review.googlesource.com/c/go/+/414834
Reviewed-by: Matthew Dempsky <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: David Chase <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>

src/cmd/compile/internal/noder/stencil.go

@@ -1214,7 +1214,7 @@ func (subst *subster) node(n ir.Node) ir.Node {
 			if m.Tag != nil && m.Tag.Op() == ir.OTYPESW {
 				break // Nothing to do here for type switches.
 			}
-			if m.Tag != nil && !m.Tag.Type().IsInterface() && m.Tag.Type().HasShape() {
+			if m.Tag != nil && !m.Tag.Type().IsEmptyInterface() && m.Tag.Type().HasShape() {
 				// To implement a switch on a value that is or has a type parameter, we first convert
 				// that thing we're switching on to an interface{}.
 				m.Tag = assignconvfn(m.Tag, types.Types[types.TINTER])
@@ -1223,7 +1223,7 @@ func (subst *subster) node(n ir.Node) ir.Node {
 				for i, x := range c.List {
 					// If we have a case that is or has a type parameter, convert that case
 					// to an interface{}.
-					if !x.Type().IsInterface() && x.Type().HasShape() {
+					if !x.Type().IsEmptyInterface() && x.Type().HasShape() {
 						c.List[i] = assignconvfn(x, types.Types[types.TINTER])
 					}
 				}

test/run.go

@@ -1964,13 +1964,9 @@ var types2Failures32Bit = setOf(
 )
 
 var go118Failures = setOf(
-	"typeparam/nested.go",      // 1.18 compiler doesn't support function-local types with generics
-	"typeparam/issue51521.go",  // 1.18 compiler produces bad panic message and link error
-	"typeparam/issue53419.go",  // 1.18 compiler mishandles generic selector resolution
-	"typeparam/issue53477.go",  // 1.18 compiler mishandles generic interface-interface comparisons from value switch statements
-	"typeparam/mdempsky/16.go", // 1.18 compiler uses interface shape type in failed type assertions
-	"typeparam/mdempsky/17.go", // 1.18 compiler mishandles implicit conversions from range loops
-	"typeparam/mdempsky/18.go", // 1.18 compiler mishandles implicit conversions in select statements
+	"typeparam/nested.go",     // 1.18 compiler doesn't support function-local types with generics
+	"typeparam/issue51521.go", // 1.18 compiler produces bad panic message and link error
+	"typeparam/issue53419.go", // 1.18 compiler mishandles generic selector resolution
 )
 
 // In all of these cases, the 1.17 compiler reports reasonable errors, but either the