On Mon, May 5, 2025 at 3:45 AM Andrew Pinski <quic_apin...@quicinc.com> wrote:
>
> Like the patch to phiopt (r15-4033-g1f619fe25925a5f7), this adds rewriting
> of VCE to gimple_with_undefined_signed_overflow/rewrite_to_defined_overflow.
> I have not seen a case yet for needing this rewrite but this step is needed
> to use gimple_with_undefined_signed_overflow/rewrite_to_defined_overflow from
> phiopt.
So what again was the "undefinedness" here? And why is this relevant
for _signed overflow_? Wouldn't it be at least no problem to V_C_E
a lower-precision value to a higher precision?
Maybe we should simply reject V_C_Es of non-mode-precision entities
on GIMPLE, much like we reject BIT_FIELD_REFs of those.
> Bootstrappd and tested on x86_64-linux-gnu.
>
> gcc/ChangeLog:
>
> PR tree-optimization/116939
> * gimple-fold.cc (gimple_with_undefined_signed_overflow): Return true
> for VCE with integral types.
> (rewrite_to_defined_overflow): Handle VCE rewriting to a cast.
>
> Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
> ---
> gcc/gimple-fold.cc | 30 ++++++++++++++++++++++++++++--
> 1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
> index c060ef81a42..a6a7fcbb8c1 100644
> --- a/gcc/gimple-fold.cc
> +++ b/gcc/gimple-fold.cc
> @@ -10602,6 +10602,14 @@ gimple_with_undefined_signed_overflow (gimple *stmt)
> if (!INTEGRAL_TYPE_P (lhs_type)
> && !POINTER_TYPE_P (lhs_type))
> return false;
> + tree rhs = gimple_assign_rhs1 (stmt);
> + /* VCE from integral types to another integral types but with
> + different precisions need to be changed into casts
> + to be well defined. */
> + if (gimple_assign_rhs_code (stmt) == VIEW_CONVERT_EXPR
> + && INTEGRAL_TYPE_P (TREE_TYPE (TREE_OPERAND (rhs, 0)))
> + && is_gimple_val (TREE_OPERAND (rhs, 0)))
> + return true;
> if (!TYPE_OVERFLOW_UNDEFINED (lhs_type))
> return false;
> if (!arith_code_with_undefined_signed_overflow
> @@ -10630,10 +10638,28 @@ rewrite_to_defined_overflow (gimple_stmt_iterator
> *gsi, gimple *stmt,
> "overflow ");
> print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
> }
> -
> + gimple_seq stmts = NULL;
> + /* VCE from integral types to another integral types but with
> + different precisions need to be changed into casts
> + to be well defined. */
> + if (gimple_assign_rhs_code (stmt) == VIEW_CONVERT_EXPR)
> + {
> + tree rhs = gimple_assign_rhs1 (stmt);
> + tree new_rhs = TREE_OPERAND (rhs, 0);
> + gcc_assert (is_gimple_val (new_rhs));
> + gimple_assign_set_rhs_code (stmt, NOP_EXPR);
> + gimple_assign_set_rhs1 (stmt, new_rhs);
> + if (in_place)
> + update_stmt (stmt);
> + else
> + {
> + gimple_set_modified (stmt, true);
> + gimple_seq_add_stmt (&stmts, stmt);
> + }
> + return stmts;
> + }
> tree lhs = gimple_assign_lhs (stmt);
> tree type = unsigned_type_for (TREE_TYPE (lhs));
> - gimple_seq stmts = NULL;
> if (gimple_assign_rhs_code (stmt) == ABS_EXPR)
> gimple_assign_set_rhs_code (stmt, ABSU_EXPR);
> else
> --
> 2.34.1
>
