[PATCH 1/2] target/s390x: Fix determination of overflow condition code after addition

[Thomas Huth]

This program currently prints different results when run with TCG instead
of running on real s390x hardware:

 #include <stdio.h>

 int overflow_32 (int x, int y)
 {
   int sum;
   return ! __builtin_add_overflow (x, y, &sum);
 }

 int overflow_64 (long long x, long long y)
 {
   long sum;
   return ! __builtin_add_overflow (x, y, &sum);
 }

 int a1 = -2147483648;
 int b1 = -2147483648;
 long long a2 = -9223372036854775808L;
 long long b2 = -9223372036854775808L;

 int main ()
 {
   {
     int a = a1;
     int b = b1;
     printf ("a = 0x%x, b = 0x%x\n", a, b);
     printf ("no_overflow = %d\n", overflow_32 (a, b));
   }
   {
     long long a = a2;
     long long b = b2;
     printf ("a = 0x%llx, b = 0x%llx\n", a, b);
     printf ("no_overflow = %d\n", overflow_64 (a, b));
   }
 }

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/616
Suggested-by: Bruno Haible <bruno@clisp.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 target/s390x/tcg/cc_helper.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/s390x/tcg/cc_helper.c b/target/s390x/tcg/cc_helper.c
index 8d04097f78..e11cdb745d 100644
--- a/target/s390x/tcg/cc_helper.c
+++ b/target/s390x/tcg/cc_helper.c
@@ -136,7 +136,7 @@ static uint32_t cc_calc_subu(uint64_t borrow_out, uint64_t 
result)
 
 static uint32_t cc_calc_add_64(int64_t a1, int64_t a2, int64_t ar)
 {
-    if ((a1 > 0 && a2 > 0 && ar < 0) || (a1 < 0 && a2 < 0 && ar > 0)) {
+    if ((a1 > 0 && a2 > 0 && ar < 0) || (a1 < 0 && a2 < 0 && ar >= 0)) {
         return 3; /* overflow */
     } else {
         if (ar < 0) {
@@ -196,7 +196,7 @@ static uint32_t cc_calc_comp_64(int64_t dst)
 
 static uint32_t cc_calc_add_32(int32_t a1, int32_t a2, int32_t ar)
 {
-    if ((a1 > 0 && a2 > 0 && ar < 0) || (a1 < 0 && a2 < 0 && ar > 0)) {
+    if ((a1 > 0 && a2 > 0 && ar < 0) || (a1 < 0 && a2 < 0 && ar >= 0)) {
         return 3; /* overflow */
     } else {
         if (ar < 0) {
-- 
2.27.0