[gcc r14-323] Avoid more invalid GIMPLE with register bases

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:977a43f5ba778b5c5cf9c56ba04ed4fde5d1ae78

commit r14-323-g977a43f5ba778b5c5cf9c56ba04ed4fde5d1ae78
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Apr 28 09:25:16 2023 +0200

    Avoid more invalid GIMPLE with register bases
    
    The Ada frontend, for example with gnat.dg/inline2_pkg.adb, tends
    to create VIEW_CONVERT expressions with aggregate type even of
    non-aggregate entities.  In this case for example
    
      return <retval> = (BIT_FIELD_REF <VIEW_CONVERT_EXPR<struct inline2_pkg__ieee_short_real>(number), 16, 16> & 32640) != 32640;
    
    currently gimplification and SSA rewrite turn this into
    
      _1 = BIT_FIELD_REF <VIEW_CONVERT_EXPR<struct inline2_pkg__ieee_short_real>(number_2(D));
    
    which is two operations on a register.  While as seen with PR109652
    we might not want to completely rule out register to aggregate type
    VIEW_CONVERTs we definitely do not want to stack multiple ops here.
    
    The solution is to make sure the gimplifier puts a non-register as
    the base object.  For the above this will add
    
      number.1 = number;
    
    and use number.1 in the compound reference.  Code generation is
    unchanged, FRE optimizes this to BIT_FIELD_REF <number_2(D), ...>.
    I think BIT_FIELD_REF <VIEW_CONVERT (x), ...> could be always
    rewritten into BIT_FIELD_REF <x, ...>, but that's a separate thing.
    
            * gimplify.cc (gimplify_compound_lval): When there's a
            non-register type produced by one of the handled component
            operations make sure we get a non-register base.

Diff:
---
 gcc/gimplify.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
index c38a962dd04..3740a8979af 100644
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -3264,6 +3264,11 @@ gimplify_compound_lval (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
 	    }
 	  need_non_reg = true;
 	}
+      else if (!is_gimple_reg_type (TREE_TYPE (t)))
+	/* When the result of an operation, in particular a VIEW_CONVERT_EXPR
+	   is a non-register type then require the base object to be a
+	   non-register as well.  */
+	need_non_reg = true;
     }
 
   /* Step 2 is to gimplify the base expression.  Make sure lvalue is set