cfgexpand sorts variables by decreasing size, so when merging a later
variable into an earlier one, there's usually no need to update the
merged size.
But for poly_int sizes, the sort function just uses a lexicographical
comparison of the coefficients, so e.g. 2X+2 comes before 0X+32.
Which is bigger depends on the runtime value of X.
This patch therefore takes the upper bound of the two sizes, which
is conservatively correct for variable-length vectors and a no-op
on other targets.
It's probably a bad idea to merge fixed-length and variable-length
variables in practice, but that's really an optimisation decision.
I think we should have this patch as a correctness fix either way.
This is easiest to test using the ACLE, but in principle it could happen
for autovectorised code too, e.g. when using OpenMP vector variables.
It's therefore a regression from GCC 8.
Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Richard
2020-01-22 Richard Sandiford <richard.sandif...@arm.com>
gcc/
* cfgexpand.c (union_stack_vars): Update the size.
gcc/testsuite/
* gcc.target/aarch64/sve/acle/general/stack_vars_1.c: New test.
---
gcc/cfgexpand.c | 3 ++
.../aarch64/sve/acle/general/stack_vars_1.c | 32 +++++++++++++++++++
2 files changed, 35 insertions(+)
create mode 100644
gcc/testsuite/gcc.target/aarch64/sve/acle/general/stack_vars_1.c
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index fb0575b146e..9864e4344d2 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -862,6 +862,9 @@ union_stack_vars (size_t a, size_t b)
stack_vars[b].representative = a;
stack_vars[a].next = b;
+ /* Make sure A is big enough to hold B. */
+ stack_vars[a].size = upper_bound (stack_vars[a].size, stack_vars[b].size);
+
/* Update the required alignment of partition A to account for B. */
if (stack_vars[a].alignb < stack_vars[b].alignb)
stack_vars[a].alignb = stack_vars[b].alignb;
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/stack_vars_1.c
b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/stack_vars_1.c
new file mode 100644
index 00000000000..860fa67fbe6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/stack_vars_1.c
@@ -0,0 +1,32 @@
+/* { dg-do run { target aarch64_sve_hw } } */
+/* { dg-additional-options "-O2" } */
+
+#include <arm_sve.h>
+
+struct s { int x[32]; };
+
+void __attribute__((noipa)) consume (void *ptr) {}
+
+void __attribute__((noipa))
+check_var (svint32_t *ptr)
+{
+ svbool_t pg = svptrue_b8 ();
+ if (svptest_any (pg, svcmpne (pg, *ptr, svindex_s32 (0, 1))))
+ __builtin_abort ();
+}
+
+int
+main (void)
+{
+ svint32_t res = svindex_s32 (0, 1);
+ {
+ __SVBool_t pg = svptrue_b8 ();
+ consume (&pg);
+ }
+ {
+ struct s zeros = { 0 };
+ consume (&zeros);
+ }
+ check_var (&res);
+ return 0;
+}
