Re: [PATCH] lower-bitint: Force some arrays corresponding to large/huge _BitInt SSA_NAMEs to BLKmode

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Jan 18, 2024 at 01:34:53PM +0100, Richard Biener wrote:
> So - if we simply do
> 
>       /* If the input and output modes are both the same, we are done.  */
>       if (mode == GET_MODE (op0) || (mode == BLKmode && MEM_P (op0))
>         ;
> 
> ?  After all if we want BLKmode we want a MEM, and if we have one
> we should be done already.  V_C_E isn't supposed to do any value
> transform.

We'd need to make sure that op0 is actually MEM, which is not the case.

The following patch seems to work though, the discover_nonconstant_array_refs_r
part helps for -O2, the expr.cc part is needed at all optimization levels.

2024-01-18  Jakub Jelinek  <jakub@redhat.com>

	* cfgexpand.cc (discover_nonconstant_array_refs_r): Force non-BLKmode
	VAR_DECLs referenced in BLKmode VIEW_CONVERT_EXPRs into memory.
	* expr.cc (expand_expr_real_1) <case VIEW_CONVERT_EXPR>: If mode is
	BLKmode and type a BITINT_TYPE from a non-BLKmode VAR_P with MEM
	DECL_RTL, use adjust_address to BLKmode for it instead of expand_expr.

--- gcc/cfgexpand.cc.jj	2024-01-16 11:45:16.159326506 +0100
+++ gcc/cfgexpand.cc	2024-01-18 13:41:54.579551282 +0100
@@ -6380,11 +6380,16 @@ discover_nonconstant_array_refs_r (tree
   /* References of size POLY_INT_CST to a fixed-size object must go
      through memory.  It's more efficient to force that here than
      to create temporary slots on the fly.
-     RTL expansion expectes TARGET_MEM_REF to always address actual memory.  */
+     RTL expansion expectes TARGET_MEM_REF to always address actual memory.
+     Also, force to stack non-BLKmode vars accessed through VIEW_CONVERT_EXPR
+     to BLKmode BITINT_TYPEs.  */
   else if (TREE_CODE (t) == TARGET_MEM_REF
 	   || (TREE_CODE (t) == MEM_REF
 	       && TYPE_SIZE (TREE_TYPE (t))
-	       && POLY_INT_CST_P (TYPE_SIZE (TREE_TYPE (t)))))
+	       && POLY_INT_CST_P (TYPE_SIZE (TREE_TYPE (t))))
+	   || (TREE_CODE (t) == VIEW_CONVERT_EXPR
+	       && TREE_CODE (TREE_TYPE (t)) == BITINT_TYPE
+	       && TYPE_MODE (TREE_TYPE (t)) == BLKmode))
     {
       tree base = get_base_address (t);
       if (base
--- gcc/expr.cc.jj	2024-01-12 10:07:58.194851657 +0100
+++ gcc/expr.cc	2024-01-18 13:38:19.677556646 +0100
@@ -12382,6 +12382,17 @@ expand_expr_real_1 (tree exp, rtx target
 	  }
       }
 
+      /* Ensure non-BLKmode array VAR_DECLs VCEd to BLKmode BITINT_TYPE
+	 aren't promoted to registers.  */
+      if (op0 == NULL_RTX
+	  && mode == BLKmode
+	  && TREE_CODE (type) == BITINT_TYPE
+	  && VAR_P (treeop0)
+	  && DECL_MODE (treeop0) != BLKmode
+	  && DECL_RTL_SET_P (treeop0)
+	  && MEM_P (DECL_RTL (treeop0)))
+	op0 = adjust_address (DECL_RTL (treeop0), BLKmode, 0);
+
       if (!op0)
 	op0 = expand_expr_real (treeop0, NULL_RTX, VOIDmode, modifier,
 				NULL, inner_reference_p);


	Jakub