Fix target/101934: aarch64 memset code creates unaligned stores for -mstrict-align

The problem here is the aarch64_expand_setmem code did not check
STRICT_ALIGNMENT if it is creating an overlapping store.
This patch adds that check and the testcase works.

gcc/ChangeLog:

	PR target/101934
	* config/aarch64/aarch64.c (aarch64_expand_setmem):
	Check STRICT_ALIGNMENT before creating an overlapping
	store.

gcc/testsuite/ChangeLog:

	PR target/101934
	* gcc.target/aarch64/memset-strict-align-1.c: New test.

(cherry picked from commit a45786e9a31f995087d8cb42bc3a4fe06911e588)

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index ae769fd79cf4bba617d9c6626e91923fb35f464d..66c7802a579a933390bc44756882007c177b1c56 100644 (file)
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -23598,8 +23598,8 @@ aarch64_expand_setmem (rtx *operands)
       /* Do certain trailing copies as overlapping if it's going to be
         cheaper.  i.e. less instructions to do so.  For instance doing a 15
         byte copy it's more efficient to do two overlapping 8 byte copies than
-        8 + 4 + 2 + 1.  */
-      if (n > 0 && n < copy_limit / 2)
+        8 + 4 + 2 + 1.  Only do this when -mstrict-align is not supplied.  */
+      if (n > 0 && n < copy_limit / 2 && !STRICT_ALIGNMENT)
        {
          next_mode = smallest_mode_for_size (n, MODE_INT);
          int n_bits = GET_MODE_BITSIZE (next_mode).to_constant ();

diff --git a/gcc/testsuite/gcc.target/aarch64/memset-strict-align-1.c b/gcc/testsuite/gcc.target/aarch64/memset-strict-align-1.c
new file mode 100644 (file)
index 0000000..5cdc8a4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/memset-strict-align-1.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-Os -mstrict-align" } */
+
+struct s { char x[95]; };
+void foo (struct s *);
+void bar (void) { struct s s1 = {}; foo (&s1); }
+
+/* memset (s1 = {}, sizeof = 95) should be expanded out
+   such that there are no overlap stores when -mstrict-align
+   is in use.
+   so 2 pair 16 bytes stores (64 bytes).
+   1 16 byte stores
+   1 8 byte store
+   1 4 byte store
+   1 2 byte store
+   1 1 byte store
+   */
+
+/* { dg-final { scan-assembler-times "stp\tq" 2 } } */
+/* { dg-final { scan-assembler-times "str\tq" 1 } } */
+/* { dg-final { scan-assembler-times "str\txzr" 1 } } */
+/* { dg-final { scan-assembler-times "str\twzr" 1 } } */
+/* { dg-final { scan-assembler-times "strh\twzr" 1 } } */
+/* { dg-final { scan-assembler-times "strb\twzr" 1 } } */
+
+/* Also one store pair for the frame-pointer and the LR. */
+/* { dg-final { scan-assembler-times "stp\tx" 1 } } */
+