Detect the special case for ISHFT for int8

When we convert int to signed short int, we first do a
sign extension, and then left shift 24 bits, followed by
arithmetic right shift 24 bits (filled with sign bits),
then followed by the real ishft, then truncate to
int8. Therefore the logical left shift never happened
to int8.

The fix is to recognize the special case for ISHFT on a
short int, and do a logical shift instead of an arithmetic
shift.

Author: gklimowicz

tools/flang2/flang2exe/exp_ftn.cpp

@@ -83,6 +83,8 @@ static int accreduct_op;
 
 #define mk_prototype mk_prototype_llvm
 
+bool ishft = false;
+
 static int
 forceK(int ili)
 {
@@ -124,6 +126,32 @@ double_is_small_int(int ilix)
   return ret_ili;
 }
 
+/**
+ * \brief check special case for ISHFT(int8)
+ */
+static bool
+is_ishft(int curilm)
+{
+  ILM *ilmp;
+  ILM_OP opc;
+  int len, bsize, ilmx;
+  len = 0;
+  bsize = ilmb.ilm_base[BOS_SIZE - 1];
+  ilmx = 0;
+  do {
+    ilmx += len;
+    ilmp = (ILM *)(ilmb.ilm_base + curilm + ilmx);
+    opc = ILM_OPC(ilmp);
+    len = ilms[opc].oprs + 1;
+    if (IM_VAR(opc))
+        len += ILM_OPND(ilmp, 1);
+    if (opc == IM_JISHFT && (ILM_OPND(ilmp, 1) == curilm)) {
+      return true;
+    }
+  } while (curilm + ilmx + len < bsize);
+  return false;
+}
+
 void
 exp_ac(ILM_OP opc, ILM *ilmp, int curilm)
 {
@@ -364,7 +392,14 @@ exp_ac(ILM_OP opc, ILM *ilmp, int curilm)
       val[1] <<= 3;                      /* difference in bits */
       op2 = ad_icon(val[1]);
       tmp = ad2ili(IL_LSHIFT, op1, op2);
-      op1 = ad2ili(IL_ARSHIFT, tmp, op2);
+      if (is_ishft(curilm)) {
+        /* Special case for ishft(int8) */
+        ishft = true;
+        op1 = ad2ili(IL_URSHIFT, tmp, op2);
+        ishft = false;
+      } else {
+        op1 = ad2ili(IL_ARSHIFT, tmp, op2);
+      }
     }
     ILM_RESULT(curilm) = op1;
     return;

tools/flang2/flang2exe/iliutil.cpp

@@ -68,6 +68,7 @@ union ATOMIC_ENCODER {
 
 bool share_proc_ili = false;
 bool share_qjsr_ili = false;
+extern bool ishft;
 
 static int addarth(ILI *);
 static int red_iadd(int, INT);
@@ -5350,7 +5351,11 @@ addarth(ILI *ilip)
     } else if (ncons == 3) {
       tmp = con2v2;
       if (SHIFTOK(tmp)) {
-        res.numi[1] = URSHIFT(con1v2, tmp);
+        if (ishft) {
+          res.numi[1] = ARSHIFT(con1v2, tmp);
+        } else {
+          res.numi[1] = URSHIFT(con1v2, tmp);
+        }
         goto add_icon;
       }
     }