Richard Biener <richard.guent...@gmail.com> writes:
> On Thu, Aug 7, 2025 at 2:14 PM Richard Sandiford
> <richard.sandif...@arm.com> wrote:
>>
>> simplify_gen_subreg rejected subregs of literal constants if
>> MODE_COMPOSITE_P. This was added by the fix for PR96648 in
>> g:c0f772894b6b3cd8ed5c5dd09d0c7917f51cf70f. Jakub said:
>>
>> As for the simplify_gen_subreg change, I think it would be desirable
>> to just avoid creating SUBREGs of constants on all targets and for all
>> constants, if simplify_immed_subreg simplified, fine, otherwise punt,
>> but as we are late in GCC11 development, the patch instead guards this
>> behavior on MODE_COMPOSITE_P (outermode) - i.e. only conversions to
>> powerpc{,64,64le} double double long double - and only for the cases where
>> simplify_immed_subreg was called.
>>
>> I'm not sure about relaxing the codes further, since subregs might
>> be wanted for CONST, SYMBOL_REF and LABEL_REF. But removing the
>> MODE_COMPOSITE_P is needed to fix PR120718, where we get an ICE
>> from generating a subreg of a V2SI const_vector.
>>
>> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
>
> OK.
Thanks! Removing the VOIDmode test exposed a latent issue on powerpc
(PR121501), so I kept that test for the backport. Pushed to GCC 15
as hopefully an obvious variation.
Richard
------------------------------------------------------------------------
simplify_gen_subreg rejected subregs of literal constants if
MODE_COMPOSITE_P. This was added by the fix for PR96648 in
g:c0f772894b6b3cd8ed5c5dd09d0c7917f51cf70f. Jakub said:
As for the simplify_gen_subreg change, I think it would be desirable
to just avoid creating SUBREGs of constants on all targets and for all
constants, if simplify_immed_subreg simplified, fine, otherwise punt,
but as we are late in GCC11 development, the patch instead guards this
behavior on MODE_COMPOSITE_P (outermode) - i.e. only conversions to
powerpc{,64,64le} double double long double - and only for the cases where
simplify_immed_subreg was called.
I'm not sure about relaxing the codes further, since subregs might
be wanted for CONST, SYMBOL_REF and LABEL_REF. But removing the
MODE_COMPOSITE_P is needed to fix PR120718, where we get an ICE
from generating a subreg of a V2SI const_vector.
Unlike the trunk version, this backport does not remove the
VOIDmode test; see PR121501.
gcc/
PR rtl-optimization/120718
* simplify-rtx.cc (simplify_context::simplify_gen_subreg):
Remove MODE_COMPOSITE_P condition.
gcc/testsuite/
PR rtl-optimization/120718
* gcc.target/aarch64/sve/acle/general/pr120718.c: New test.
---
gcc/simplify-rtx.cc | 13 +++++--------
.../gcc.target/aarch64/sve/acle/general/pr120718.c | 12 ++++++++++++
2 files changed, 17 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index 88d31a71c05..8d4cbf1371a 100644
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -8317,14 +8317,11 @@ simplify_context::simplify_gen_subreg (machine_mode
outermode, rtx op,
if (GET_CODE (op) == SUBREG
|| GET_CODE (op) == CONCAT
- || GET_MODE (op) == VOIDmode)
- return NULL_RTX;
-
- if (MODE_COMPOSITE_P (outermode)
- && (CONST_SCALAR_INT_P (op)
- || CONST_DOUBLE_AS_FLOAT_P (op)
- || CONST_FIXED_P (op)
- || GET_CODE (op) == CONST_VECTOR))
+ || GET_MODE (op) == VOIDmode
+ || CONST_SCALAR_INT_P (op)
+ || CONST_DOUBLE_AS_FLOAT_P (op)
+ || CONST_FIXED_P (op)
+ || GET_CODE (op) == CONST_VECTOR)
return NULL_RTX;
if (validate_subreg (outermode, innermode, op, byte))
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
new file mode 100644
index 00000000000..9ca0938e36b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr120718.c
@@ -0,0 +1,12 @@
+/* { dg-options "-O2" } */
+
+#include <arm_sve.h>
+typedef int __attribute__((vector_size(8))) v2si;
+typedef struct { int x; int y; } A;
+void bar(A a);
+void foo()
+{
+ A a;
+ *(v2si *)&a = (v2si){0, (int)svcntd_pat(SV_ALL)};
+ bar(a);
+}
--
2.43.0
