From: Richard Earnshaw <rearnsha@arm.com>
Date: Tue, 24 Nov 2020 16:21:17 +0000 (+0000)
Subject: arm: correctly handle negating INT_MIN in arm_split_atomic_op [PR97534]
X-Git-Tag: releases/gcc-10.3.0~596
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dd2c4e4e97331b1b3d9081191d14f8967d73e31c;p=thirdparty%2Fgcc.git

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 99b1e926dc30..b4d7b5bc5073 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -30582,7 +30582,7 @@ 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
index 000000000000..b363a322aa54
--- /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);
+}