> Ah - tree_ssa_useless_type_conversion and callers, during gimplification.
> I'd like to get rid of it but maybe simply delete the VIEW_CONVERT_EXPR
> case from it for now (and return true unconditionally for NON_LVALUE_EXPR).
>
> Index: gcc/tree-ssa.c
> ===================================================================
> --- gcc/tree-ssa.c (revision 229517)
> +++ gcc/tree-ssa.c (working copy)
> @@ -1142,13 +1161,16 @@ delete_tree_ssa (struct function *fn)
> bool
> tree_ssa_useless_type_conversion (tree expr)
> {
> + /* Not strictly a conversion but this function is used to strip
> + useless stuff from trees returned from GENERIC folding. */
> + if (TREE_CODE (expr) == NON_LVALUE_EXPR)
> + return true;
> +
> /* If we have an assignment that merely uses a NOP_EXPR to change
> the top of the RHS to the type of the LHS and the type conversion
> is "safe", then strip away the type conversion so that we can
> enter LHS = RHS into the const_and_copies table. */
> - if (CONVERT_EXPR_P (expr)
> - || TREE_CODE (expr) == VIEW_CONVERT_EXPR
> - || TREE_CODE (expr) == NON_LVALUE_EXPR)
> + if (CONVERT_EXPR_P (expr))
> return useless_type_conversion_p
> (TREE_TYPE (expr),
> TREE_TYPE (TREE_OPERAND (expr, 0)));
The patch introduces GIMPLE checking failures:
FAIL: c52103m
FAIL: c52103r
FAIL: c52104m
FAIL: c52104r
of the form:
slice9.adb: In function 'Slice9':
slice9.adb:1:1: error: conversion of an SSA_NAME on the left hand side
VIEW_CONVERT_EXPR<character[D.4195:iftmp.10]>("ABCDE");
D.4379 = &VIEW_CONVERT_EXPR<character[D.4195:iftmp.10]>("ABCDE")[D.4378 ...]
{lb: D.4195 sz: 1};
if (TREE_CODE (expr) == VIEW_CONVERT_EXPR)
{
/* For VIEW_CONVERT_EXPRs which are allowed here too, we only check
that their operand is not an SSA name or an invariant when
requiring an lvalue (this usually means there is a SRA or IPA-SRA
bug). Otherwise there is nothing to verify, gross mismatches at
most invoke undefined behavior. */
if (require_lvalue
&& (TREE_CODE (op) == SSA_NAME
|| is_gimple_min_invariant (op)))
{
error ("conversion of an SSA_NAME on the left hand side");
debug_generic_stmt (expr);
return true;
}
else if (TREE_CODE (op) == SSA_NAME
&& TYPE_SIZE (TREE_TYPE (expr)) != TYPE_SIZE (TREE_TYPE (op)))
{
error ("conversion of register to a different size");
debug_generic_stmt (expr);
return true;
}
else if (!handled_component_p (op))
return false;
}
It's related to dynamic slicing (reduced testcase attached).
* gnat.dg/slice9.adb: New test.
--
Eric Botcazou
-- { dg-do compile }
procedure Slice9 is
function Ident (I : Integer) return Integer is
begin
return I;
end;
subtype S is String (Ident(5)..Ident(9));
Dest : S;
Src : String (Ident(1)..Ident(5)) := "ABCDE";
begin
Dest (Ident(5)..Ident(7)) := Src (Ident(1)..Ident(3));
end;