[committed] aarch64: Fix up __aarch64_cas16_acq_rel fallback [PR96402]

Jakub Jelinek jakub@redhat.com
Mon Aug 3 21:00:18 GMT 2020


Hi!

As mentioned in the PR, the fallback path when LSE is unavailable writes
incorrect registers to the memory if the previous content compares equal
to x0, x1 - it writes copy of x0, x1 from the start of function, but it
should write x2, x3.

Fixed thusly, bootstrapped/regtested on aarch64-linux (without LSE),
preapproved in the PR by Kyrylo, committed to trunk and 10.3.

2020-08-03  Jakub Jelinek  <jakub@redhat.com>

	PR target/96402
	* config/aarch64/lse.S (__aarch64_cas16_acq_rel): Use x2, x3 instead
	of x(tmp0), x(tmp1) in STXP arguments.

	* gcc.target/aarch64/pr96402.c: New test.

--- gcc/testsuite/gcc.target/aarch64/pr96402.c.jj	2020-08-03 11:11:50.136698905 +0200
+++ gcc/testsuite/gcc.target/aarch64/pr96402.c	2020-08-03 11:13:38.087168812 +0200
@@ -0,0 +1,16 @@
+/* PR target/96402 */
+/* { dg-do run { target int128 } } */
+/* { dg-options "-moutline-atomics" } */
+
+int
+main ()
+{
+  __int128 a = 0;
+  __sync_val_compare_and_swap (&a, (__int128) 0, (__int128) 1);
+  if (a != 1)
+    __builtin_abort ();
+  __sync_val_compare_and_swap (&a, (__int128) 1, (((__int128) 0xdeadbeeffeedbac1ULL) << 64) | 0xabadcafe00c0ffeeULL);
+  if (a != ((((__int128) 0xdeadbeeffeedbac1ULL) << 64) | 0xabadcafe00c0ffeeULL))
+    __builtin_abort ();
+  return 0;
+}
--- libgcc/config/aarch64/lse.S.jj	2020-07-28 15:39:10.134754495 +0200
+++ libgcc/config/aarch64/lse.S	2020-08-03 11:04:17.544113977 +0200
@@ -203,7 +203,7 @@ STARTFN	NAME(cas)
 	cmp		x0, x(tmp0)
 	ccmp		x1, x(tmp1), #0, eq
 	bne		1f
-	STXP		w(tmp2), x(tmp0), x(tmp1), [x4]
+	STXP		w(tmp2), x2, x3, [x4]
 	cbnz		w(tmp2), 0b
 1:	ret
 


	Jakub



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