From: Richard Henderson <richard.henderson@linaro.org>

The 'sign' computation is attempting to locate the sign bit that has
been repeated, so that we can test if that bit is known zero.  That
computation can be zero if there are no known sign repetitions.

Cc: qemu-stable@nongnu.org
Fixes: 93a967fbb57 ("tcg/optimize: Propagate sign info for shifting")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2248
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
(cherry picked from commit 2911e9b95f3bb03783ae5ca3e2494dc3b44a9161)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: trivial context fixup in tests/tcg/aarch64/Makefile.target)

diff --git a/tcg/optimize.c b/tcg/optimize.c
index ae081ab29c..b6f6436c74 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -1907,7 +1907,7 @@ static bool fold_shift(OptContext *ctx, TCGOp *op)
          * will not reduced the number of input sign repetitions.
          */
         sign = (s_mask & -s_mask) >> 1;
-        if (!(z_mask & sign)) {
+        if (sign && !(z_mask & sign)) {
             ctx->s_mask = s_mask;
         }
         break;
diff --git a/tests/tcg/aarch64/Makefile.target b/tests/tcg/aarch64/Makefile.target
index 5e4ea7c998..474f61bc30 100644
--- a/tests/tcg/aarch64/Makefile.target
+++ b/tests/tcg/aarch64/Makefile.target
@@ -10,6 +10,7 @@ VPATH 		+= $(AARCH64_SRC)
 
 # Base architecture tests
 AARCH64_TESTS=fcvt pcalign-a64
+AARCH64_TESTS += test-2248
 
 fcvt: LDFLAGS+=-lm
 
diff --git a/tests/tcg/aarch64/test-2248.c b/tests/tcg/aarch64/test-2248.c
new file mode 100644
index 0000000000..aac2e17836
--- /dev/null
+++ b/tests/tcg/aarch64/test-2248.c
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* See https://gitlab.com/qemu-project/qemu/-/issues/2248 */
+
+#include <assert.h>
+
+__attribute__((noinline))
+long test(long x, long y, long sh)
+{
+    long r;
+    asm("cmp   %1, %2\n\t"
+        "cset  x12, lt\n\t"
+        "and   w11, w12, #0xff\n\t"
+        "cmp   w11, #0\n\t"
+        "csetm x14, ne\n\t"
+        "lsr   x13, x14, %3\n\t"
+        "sxtb  %0, w13"
+        : "=r"(r)
+        : "r"(x), "r"(y), "r"(sh)
+        : "x11", "x12", "x13", "x14");
+    return r;
+}
+
+int main()
+{
+    long r = test(0, 1, 2);
+    assert(r == -1);
+    return 0;
+}
-- 
2.39.2