arm: correctly handle negating INT_MIN in arm_split_atomic_op [PR97534]

arm_split_atomic_op handles subtracting a constant by converting it
into addition of the negated constant.  But if the type of the operand
is int and the constant is -1 we currently end up generating invalid
RTL which can lead to an abort later on.

The problem is that in a HOST_WIDE_INT, INT_MIN is represented as
0xffffffff80000000 and the negation of this is 0x0000000080000000, but
that's not a valid constant for use in SImode operations.

The fix is straight-forward which is to use gen_int_mode rather than
simply GEN_INT.  This knows how to correctly sign-extend the negated
constant when this is needed.

gcc/
	PR target/97534
	* config/arm/arm.c (arm_split_atomic_op): Use gen_int_mode when
	negating a const_int.
gcc/testsuite
	* gcc.dg/pr97534.c: New test.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 568e1530f24d2045fa80b91103556a86825aa148..56ed556b098bc042b912d6dfee4fede8299489d5 100644 (file)
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -30824,7 +30824,7 @@ arm_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
     case MINUS:
       if (CONST_INT_P (value))
        {
-         value = GEN_INT (-INTVAL (value));
+         value = gen_int_mode (-INTVAL (value), wmode);
          code = PLUS;
        }
       /* FALLTHRU */

diff --git a/gcc/testsuite/gcc.dg/pr97534.c b/gcc/testsuite/gcc.dg/pr97534.c
new file mode 100644 (file)
index 0000000..b363a32
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr97534.c
@@ -0,0 +1,9 @@
+/* PR target/97534 - ICE in decompose on arm*-*-*.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -O2 -g" } */
+
+int f (int a)
+{
+  int b;
+  __atomic_fetch_sub(&b, (int)(-__INT_MAX__ - 1), (int)0);
+}