On 13/10/26 23:55, Andrea Pinski wrote:
External email: Use caution opening links or attachments
On Mon, Oct 12, 2026 at 1:47 AM <[email protected]> wrote:
From: Dhruv Chawla <[email protected]>
r17-4816-gb24418a2212866 gives a call whose result is discarded a placeholder
lhs using create_tmp_var, which gives a VAR_DECL. This ends up setting
ssa_renaming_needed and the subsequent fold passes do not set TODO_update_ssa,
so execute_todo ICEs. This is only set for register types and not for
aggregates, like svfloat32x2_t, which cannot be made via make_ssa_name
regardless. Thus, only generate the SSA name when is_gimple_reg_type is
true.
This needs the fold to run after SSA construction. In the testcase the second
operand is not yet a constant when intrinsics are first folded from
gimple-low, so the fold only succeeds once CCP has executed.
Bootstrapped and regtested on aarch64-linux-gnu.
Signed-off-by: Dhruv Chawla <[email protected]>
gcc/ChangeLog:
PR target/127771
* config/aarch64/aarch64-acle-builtins.cc: Include ssa.h.
(gimple_folder::fold): Make an SSA name for the placeholder when
is_gimple_reg_type and release it when unused.
What about this alternative patch? This should be less fragile though
it requires some more changes than the current approach.
I have not tested it either so there might be some typos.
Does this preserve calls to FP intrinsics? The temp LHS fix was caused
by them not being removed by DCE as they could modify the FP env. Folding
them to GIMPLE_NOP in that case would be wrong.
--
Regards,
Dhruv
gcc/testsuite/ChangeLog:
PR target/127771
* gcc.target/aarch64/sve/acle/general/pr127771.c: New test.
---
gcc/config/aarch64/aarch64-acle-builtins.cc | 37 ++++++++++++++++---
.../aarch64/sve/acle/general/pr127771.c | 21 +++++++++++
2 files changed, 52 insertions(+), 6 deletions(-)
create mode 100644
gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr127771.c
diff --git a/gcc/config/aarch64/aarch64-acle-builtins.cc
b/gcc/config/aarch64/aarch64-acle-builtins.cc
index 5abcc01b96bf..238570d9becd 100644
--- a/gcc/config/aarch64/aarch64-acle-builtins.cc
+++ b/gcc/config/aarch64/aarch64-acle-builtins.cc
@@ -46,6 +46,7 @@
#include "gimple-fold.h"
#include "langhooks.h"
#include "stringpool.h"
+#include "ssa.h"
#include "attribs.h"
#include "value-range.h"
#include "tree-ssanames.h"
@@ -3142,16 +3143,40 @@ gimple_folder::fold ()
/* Create a placeholder variable for the result.
This allows implementers of `fold` to assume `lhs` will never be null.
If the result is unused, it will be optimized away later. */
+ tree placeholder = NULL_TREE;
if (!lhs && TREE_TYPE (gimple_call_fntype (call)) != void_type_node)
- lhs = create_tmp_var (TREE_TYPE (gimple_call_fntype (call)));
+ {
+ tree type = TREE_TYPE (gimple_call_fntype (call));
+
+ /* PR target/127771: A register result has to be an SSA name as VAR_DECLs
+ created via create_tmp_var set ssa_renaming_needed and the fold passes
+ do not set TODO_update_ssa, so execute_todo ICEs. Aggregates cannot be
+ SSA names at all, but they do not set that flag either, so a
+ declaration is both necessary and safe for them. */
+ if (is_gimple_reg_type (type))
+ lhs = placeholder = make_ssa_name (type);
+ else
+ lhs = create_tmp_var (type);
+ }
/* First try some simplifications that are common to many functions. */
- if (auto *call = redirect_pred_x ())
- return call;
- if (auto *call = fold_pfalse ())
- return call;
+ gimple *stmt = redirect_pred_x ();
+ if (!stmt)
+ stmt = fold_pfalse ();
+ if (!stmt)
+ stmt = base->fold (*this);
+
+ /* Release a placeholder that nothing defines and nothing uses, because
+ gimple_build_assign does not set the definition until insertion and
+ convert_and_fold returns a different statement from the one it inserts.
*/
+ if (placeholder && (!stmt || gimple_get_lhs (stmt) != placeholder))
+ {
+ gimple *def = SSA_NAME_DEF_STMT (placeholder);
+ if (has_zero_uses (placeholder) && (!def || gimple_nop_p (def)))
+ release_ssa_name (placeholder);
+ }
- return base->fold (*this);
+ return stmt;
}
/* Force EXPR to be a GIMPLE value, putting it into a new variable if
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr127771.c
b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr127771.c
new file mode 100644
index 000000000000..0a024ca4954f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr127771.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O1" } */
+
+#include <arm_sve.h>
+
+/* PR target/127771 */
+
+void
+g (svbool_t p, svuint32_t a)
+{
+ svmul_x (p, a, svdup_u32 (1));
+}
+
+/* The placeholder for a discarded result cannot be an SSA name when the
+ return type is an aggregate. */
+
+void
+h (svuint32_t a, svuint32_t b)
+{
+ svcreate2_u32 (a, b);
+}
--
2.43.0
