Mark constant-sized objects as addressable if they have poly-int accesses

If SVE code is written for a specific vector length, it might load from
or store to fixed-sized objects.  This needs to work even without
-msve-vector-bits=N (which should never be needed for correctness).

There's no way of handling a direct poly-int sized reference to a
fixed-size register; it would have to go via memory.  And in that
case it's more efficient to mark the fixed-size object as
addressable from the outset, like we do for array references
with non-constant indices.

2019-12-03  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* cfgexpand.c (discover_nonconstant_array_refs_r): If an access
	with POLY_INT_CST size is made to a fixed-size object, force the
	object to live in memory.

gcc/testsuite/
	* gcc.target/aarch64/sve/acle/general/deref_1.c: New test.


git-svn-id: https://gcc.gnu.org/svn/gcc/trunk@278941 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 50 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 2902cdc7344..1b246171d46 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-12-03  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* cfgexpand.c (discover_nonconstant_array_refs_r): If an access
+	with POLY_INT_CST size is made to a fixed-size object, force the
+	object to live in memory.
+
 2019-12-03  Andrew Stubbs  <ams@codesourcery.com>
 
 	* config/gcn/gcn-valu.md: Change "vcondu" patterns to use VEC_1REG_MODE
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index e8bed2504bf..bb31fef7014 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -6133,6 +6133,21 @@ discover_nonconstant_array_refs_r (tree * tp, int *walk_subtrees,
 
       *walk_subtrees = 0;
     }
+  /* References of size POLY_INT_CST to a fixed-size object must go
+     through memory.  It's more efficient to force that here than
+     to create temporary slots on the fly.  */
+  else if ((TREE_CODE (t) == MEM_REF || TREE_CODE (t) == TARGET_MEM_REF)
+	   && TYPE_SIZE (TREE_TYPE (t))
+	   && POLY_INT_CST_P (TYPE_SIZE (TREE_TYPE (t))))
+    {
+      tree base = get_base_address (t);
+      if (base
+	  && DECL_P (base)
+	  && DECL_MODE (base) != BLKmode
+	  && GET_MODE_SIZE (DECL_MODE (base)).is_constant ())
+	TREE_ADDRESSABLE (base) = 1;
+      *walk_subtrees = 0;
+    }
 
   return NULL_TREE;
 }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index cc8ff79cbc2..028755bb51a 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2019-12-03  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* gcc.target/aarch64/sve/acle/general/deref_1.c: New test.
+
 2019-12-03  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/91363 - P0960R3: Parenthesized initialization of aggregates.
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/deref_1.c b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/deref_1.c
new file mode 100644
index 00000000000..99d831936a5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/deref_1.c
@@ -0,0 +1,25 @@
+/* { dg-options "-O2" } */
+
+#include <arm_sve.h>
+
+uint64_t
+f1 (int32_t *x, int32_t *y)
+{
+  union { uint64_t x; char c[8]; } u;
+  svbool_t pg = svptrue_b32 ();
+  *(svbool_t *)&u.c[0] = svcmpeq (pg, svld1 (pg, x), 0);
+  *(svbool_t *)&u.c[4] = svcmpeq (pg, svld1 (pg, y), 1);
+  return u.x;
+}
+
+typedef unsigned int v4si __attribute__((vector_size(16)));
+
+/* The aliasing is somewhat dubious here, but it must compile.  */
+
+v4si
+f2 (void)
+{
+  v4si res;
+  *(svuint32_t *) &res = svindex_u32 (0, 1);
+  return res;
+}