[Bug target/103353] Indefinite recursion when compiling -mmma requiring testcase w/ -maltivec

["linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103353

--- Comment #5 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #4)
> You miss all extra errors the expand_call can generate.  This is the general
> reason why we try to continue instead of stopping after the first error.  The
> reason is that later errors may be more obvious to the user.  This of course
> does no longer work so well because our errors now take 30 lines instead of
> 1.
> 

Thanks for the explanation! One consequent question is that this point can be
applied for the other places where some expected conditions don't hold for bif
expansion, but I saw the other places are using "return const0_rtx". Is there
something special causing this difference?

> It probably is best if the generic opaque-mode emit_move code does not try
> to move it via some other mode_class.  Peter?
> 
> Failing that, we can work around it by having move patterns for those modes
> always, but hard erroring on them (FAIL is no good).

Yeah, one workround can help the ICE gone: (similar thing needed for XOmode as
well):

diff --git a/gcc/config/rs6000/mma.md b/gcc/config/rs6000/mma.md
index 907c9d6d516..04e887ad147 100644
--- a/gcc/config/rs6000/mma.md
+++ b/gcc/config/rs6000/mma.md
@@ -268,10 +268,12 @@ (define_int_attr avvi4i4i4 [(UNSPEC_MMA_PMXVI8GER4PP     
 "pmxvi8ger4pp")
 (define_expand "movoo"
   [(set (match_operand:OO 0 "nonimmediate_operand")
         (match_operand:OO 1 "input_operand"))]
-  "TARGET_MMA"
+  ""
 {
-  rs6000_emit_move (operands[0], operands[1], OOmode);
-  DONE;
+  if (TARGET_MMA) {
+    rs6000_emit_move (operands[0], operands[1], OOmode);
+    DONE;
+  }
 })

 (define_insn_and_split "*movoo"