https://gcc.gnu.org/g:3182e95eda4a1d612b910b3248c997c8acc7add3
commit r16-3328-g3182e95eda4a1d612b910b3248c997c8acc7add3
Author: Richard Biener <rguent...@suse.de>
Date: Thu Jan 23 14:29:26 2025 +0100
tree-optimization/111494 - reduction vectorization with signed UB
The following makes sure to pun arithmetic that's used in vectorized
reduction to unsigned when overflow invokes undefined behavior.
PR tree-optimization/111494
* gimple-fold.h (arith_code_with_undefined_signed_overflow):
Declare.
* gimple-fold.cc (arith_code_with_undefined_signed_overflow):
Export.
* tree-vect-stmts.cc (vectorizable_operation): Use unsigned
arithmetic for operations participating in a reduction.
Diff:
---
gcc/gimple-fold.cc | 2 +-
gcc/gimple-fold.h | 1 +
gcc/tree-vect-stmts.cc | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 56 insertions(+), 1 deletion(-)
diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index 85319b334928..03130ce84301 100644
--- a/gcc/gimple-fold.cc
+++ b/gcc/gimple-fold.cc
@@ -10484,7 +10484,7 @@ gimple_fold_indirect_ref (tree t)
integer types involves undefined behavior on overflow and the
operation can be expressed with unsigned arithmetic. */
-static bool
+bool
arith_code_with_undefined_signed_overflow (tree_code code)
{
switch (code)
diff --git a/gcc/gimple-fold.h b/gcc/gimple-fold.h
index b678502f2fca..3f617d1c4cd7 100644
--- a/gcc/gimple-fold.h
+++ b/gcc/gimple-fold.h
@@ -58,6 +58,7 @@ extern tree gimple_get_virt_method_for_vtable (HOST_WIDE_INT,
tree,
extern tree gimple_fold_indirect_ref (tree);
extern bool gimple_fold_builtin_sprintf (gimple_stmt_iterator *);
extern bool gimple_fold_builtin_snprintf (gimple_stmt_iterator *);
+extern bool arith_code_with_undefined_signed_overflow (tree_code);
extern bool gimple_needing_rewrite_undefined (gimple *);
extern void rewrite_to_defined_unconditional (gimple_stmt_iterator *);
extern gimple_seq rewrite_to_defined_unconditional (gimple *);
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index 3c0a40f940ab..47cd29fb1b89 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -6562,6 +6562,20 @@ vectorizable_operation (vec_info *vinfo,
vec_dest = vect_create_destination_var (scalar_dest, vectype);
vec_cvt_dest = vect_create_destination_var (scalar_dest, vectype_out);
}
+ /* For reduction operations with undefined overflow behavior make sure to
+ pun them to unsigned since we change the order of evaluation.
+ ??? Avoid for in-order reductions? */
+ else if (arith_code_with_undefined_signed_overflow (orig_code)
+ && ANY_INTEGRAL_TYPE_P (vectype)
+ && TYPE_OVERFLOW_UNDEFINED (vectype)
+ && STMT_VINFO_REDUC_IDX (stmt_info) != -1)
+ {
+ gcc_assert (orig_code == PLUS_EXPR || orig_code == MINUS_EXPR
+ || orig_code == MULT_EXPR || orig_code == POINTER_PLUS_EXPR);
+ vec_cvt_dest = vect_create_destination_var (scalar_dest, vectype_out);
+ vectype = unsigned_type_for (vectype);
+ vec_dest = vect_create_destination_var (scalar_dest, vectype);
+ }
/* Handle def. */
else
vec_dest = vect_create_destination_var (scalar_dest, vectype_out);
@@ -6575,6 +6589,46 @@ vectorizable_operation (vec_info *vinfo,
vop1 = ((op_type == binary_op || op_type == ternary_op)
? vec_oprnds1[i] : NULL_TREE);
vop2 = ((op_type == ternary_op) ? vec_oprnds2[i] : NULL_TREE);
+
+ if (vec_cvt_dest
+ && !useless_type_conversion_p (vectype, TREE_TYPE (vop0)))
+ {
+ new_temp = build1 (VIEW_CONVERT_EXPR, vectype, vop0);
+ new_stmt = gimple_build_assign (vec_dest, VIEW_CONVERT_EXPR,
+ new_temp);
+ new_temp = make_ssa_name (vec_dest, new_stmt);
+ gimple_assign_set_lhs (new_stmt, new_temp);
+ vect_finish_stmt_generation (vinfo, stmt_info,
+ new_stmt, gsi);
+ vop0 = new_temp;
+ }
+ if (vop1
+ && vec_cvt_dest
+ && !useless_type_conversion_p (vectype, TREE_TYPE (vop1)))
+ {
+ new_temp = build1 (VIEW_CONVERT_EXPR, vectype, vop1);
+ new_stmt = gimple_build_assign (vec_dest, VIEW_CONVERT_EXPR,
+ new_temp);
+ new_temp = make_ssa_name (vec_dest, new_stmt);
+ gimple_assign_set_lhs (new_stmt, new_temp);
+ vect_finish_stmt_generation (vinfo, stmt_info,
+ new_stmt, gsi);
+ vop1 = new_temp;
+ }
+ if (vop2
+ && vec_cvt_dest
+ && !useless_type_conversion_p (vectype, TREE_TYPE (vop2)))
+ {
+ new_temp = build1 (VIEW_CONVERT_EXPR, vectype, vop2);
+ new_stmt = gimple_build_assign (vec_dest, VIEW_CONVERT_EXPR,
+ new_temp);
+ new_temp = make_ssa_name (vec_dest, new_stmt);
+ gimple_assign_set_lhs (new_stmt, new_temp);
+ vect_finish_stmt_generation (vinfo, stmt_info,
+ new_stmt, gsi);
+ vop2 = new_temp;
+ }
+
if (using_emulated_vectors_p)
{
/* Lower the operation. This follows vector lowering. */
