target-mips: Fix incorrect shift for SHILO and SHILOV

helper_shilo has not been shifting an accumulator value correctly for negative
values in 'shift' field. Minor optimization for shift=0 case.
This change also adds tests that will trigger issue and check for regressions.

Signed-off-by: Petar Jovanovic <petarj@mips.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Eric Johnson <ericj@mips.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

target-mips/dsp_helper.c

@@ -3814,17 +3814,18 @@ void helper_shilo(target_ulong ac, target_ulong rs, CPUMIPSState *env)
 
     rs5_0 = rs & 0x3F;
     rs5_0 = (int8_t)(rs5_0 << 2) >> 2;
-    rs5_0 = MIPSDSP_ABS(rs5_0);
+
+    if (unlikely(rs5_0 == 0)) {
+        return;
+    }
+
     acc   = (((uint64_t)env->active_tc.HI[ac] << 32) & MIPSDSP_LHI) |
             ((uint64_t)env->active_tc.LO[ac] & MIPSDSP_LLO);
-    if (rs5_0 == 0) {
-        temp = acc;
+
+    if (rs5_0 > 0) {
+        temp = acc >> rs5_0;
     } else {
-        if (rs5_0 > 0) {
-            temp = acc >> rs5_0;
-        } else {
-            temp = acc << rs5_0;
-        }
+        temp = acc << -rs5_0;
     }
 
     env->active_tc.HI[ac] = (target_ulong)(int32_t)((temp & MIPSDSP_LHI) >> 32);

tests/tcg/mips/mips32-dsp/shilo.c

@@ -23,5 +23,23 @@ int main()
     assert(ach == resulth);
     assert(acl == resultl);
 
+
+    ach = 0x1;
+    acl = 0x80000000;
+
+    resulth = 0x3;
+    resultl = 0x0;
+
+    __asm
+        ("mthi %0, $ac1\n\t"
+         "mtlo %1, $ac1\n\t"
+         "shilo $ac1, -1\n\t"
+         "mfhi %0, $ac1\n\t"
+         "mflo %1, $ac1\n\t"
+         : "+r"(ach), "+r"(acl)
+        );
+    assert(ach == resulth);
+    assert(acl == resultl);
+
     return 0;
 }

tests/tcg/mips/mips32-dsp/shilov.c

@@ -25,5 +25,25 @@ int main()
     assert(ach == resulth);
     assert(acl == resultl);
 
+
+    rs  = 0xffffffff;
+    ach = 0x1;
+    acl = 0x80000000;
+
+    resulth = 0x3;
+    resultl = 0x0;
+
+    __asm
+        ("mthi %0, $ac1\n\t"
+         "mtlo %1, $ac1\n\t"
+         "shilov $ac1, %2\n\t"
+         "mfhi %0, $ac1\n\t"
+         "mflo %1, $ac1\n\t"
+         : "+r"(ach), "+r"(acl)
+         : "r"(rs)
+        );
+    assert(ach == resulth);
+    assert(acl == resultl);
+
     return 0;
 }