re PR go/80128 (go1: internal compiler error: in write_specific_type_functions,…

re PR go/80128 (go1: internal compiler error: in write_specific_type_functions, at go/gofrontend/types.cc:2002)

	PR go/80128
    compiler: check backend alignment for memequalNN functions
    
    The code was assuming the usual required alignment for the memequalNN
    functions (16 bits for int16, 32 for int32, etc.). However, on m68k
    the required alignment of int32 is only 16 bits. Assuming the
    memequalNN alignment caused the compiler to incorrectly decide that
    int32 required a specially generated function rather than calling
    memequal32. This then crashed if the type descriptor were generated
    after type-specific functions had been written.
    
    Fixes GCC PR 80128.
    
    Reviewed-on: https://go-review.googlesource.com/38433

From-SVN: r246382

gcc/go/gofrontend/types.cc

@@ -1580,6 +1580,42 @@ Type::make_type_descriptor_ptr_type()
   return ret;
 }
 
+// Return the alignment required by the memequalN function.  N is a
+// type size: 16, 32, 64, or 128.  The memequalN functions are defined
+// in libgo/go/runtime/alg.go.
+
+int64_t
+Type::memequal_align(Gogo* gogo, int size)
+{
+  const char* tn;
+  switch (size)
+    {
+    case 16:
+      tn = "int16";
+      break;
+    case 32:
+      tn = "int32";
+      break;
+    case 64:
+      tn = "int64";
+      break;
+    case 128:
+      // The code uses [2]int64, which must have the same alignment as
+      // int64.
+      tn = "int64";
+      break;
+    default:
+      go_unreachable();
+    }
+
+  Type* t = Type::lookup_integer_type(tn);
+
+  int64_t ret;
+  if (!t->backend_type_align(gogo, &ret))
+    go_unreachable();
+  return ret;
+}
+
 // Return whether this type needs specially built type functions.
 // This returns true for types that are comparable and either can not
 // use an identity comparison, or are a non-standard size.
@@ -1614,14 +1650,13 @@ Type::needs_specific_type_functions(Gogo* gogo)
     case 0:
     case 1:
     case 2:
-      return align < 2;
+      return align < Type::memequal_align(gogo, 16);
     case 4:
-      return align < 4;
+      return align < Type::memequal_align(gogo, 32);
     case 8:
-      return align < 8;
+      return align < Type::memequal_align(gogo, 64);
     case 16:
-      // 8, not 16, because of how runtime.memequal128 is written.
-      return align < 8;
+      return align < Type::memequal_align(gogo, 128);
     default:
       return true;
     }
@@ -1713,7 +1748,7 @@ Type::type_functions(Gogo* gogo, Named_type* name, Function_type* hash_fntype,
 	  equal_fnname = "runtime.memequal8";
 	  break;
 	case 2:
-	  if (align < 2)
+	  if (align < Type::memequal_align(gogo, 16))
 	    build_functions = true;
 	  else
 	    {
@@ -1722,7 +1757,7 @@ Type::type_functions(Gogo* gogo, Named_type* name, Function_type* hash_fntype,
 	    }
 	  break;
 	case 4:
-	  if (align < 4)
+	  if (align < Type::memequal_align(gogo, 32))
 	    build_functions = true;
 	  else
 	    {
@@ -1731,7 +1766,7 @@ Type::type_functions(Gogo* gogo, Named_type* name, Function_type* hash_fntype,
 	    }
 	  break;
 	case 8:
-	  if (align < 8)
+	  if (align < Type::memequal_align(gogo, 64))
 	    build_functions = true;
 	  else
 	    {
@@ -1740,8 +1775,7 @@ Type::type_functions(Gogo* gogo, Named_type* name, Function_type* hash_fntype,
 	    }
 	  break;
 	case 16:
-	  // 8, not 16, because of how runtime.memequal128 is written.
-	  if (align < 8)
+	  if (align < Type::memequal_align(gogo, 128))
 	    build_functions = true;
 	  else
 	    {

gcc/go/gofrontend/types.h

@@ -993,6 +993,9 @@ class Type
 				const std::string& equal_name,
 				Function_type* equal_fntype);
 
+  // Return the alignment required by the memequalN function.
+  static int64_t memequal_align(Gogo*, int size);
+
   // Export the type.
   void
   export_type(Export* exp) const