IBM zSystems: Fix function_ok_for_sibcall [PR106355]

For a parameter with BLKmode we cannot use REG_NREGS in order to
determine the number of consecutive registers.  Streamlined this with
the implementation of s390_function_arg.

Fix some indentation whitespace, too.

gcc/ChangeLog:

	PR target/106355
	* config/s390/s390.cc (s390_call_saved_register_used): For a
	parameter with BLKmode fix determining number of consecutive
	registers.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/pr106355.h: Common code for new tests.
	* gcc.target/s390/pr106355-1.c: New test.
	* gcc.target/s390/pr106355-2.c: New test.
	* gcc.target/s390/pr106355-3.c: New test.

gcc/config/s390/s390.cc

@@ -13792,36 +13792,37 @@ s390_call_saved_register_used (tree call_expr)
       function_arg_info arg (TREE_TYPE (parameter), /*named=*/true);
       apply_pass_by_reference_rules (&cum_v, arg);
 
-       parm_rtx = s390_function_arg (cum, arg);
+      parm_rtx = s390_function_arg (cum, arg);
 
-       s390_function_arg_advance (cum, arg);
+      s390_function_arg_advance (cum, arg);
 
-       if (!parm_rtx)
-	 continue;
+      if (!parm_rtx)
+	continue;
 
-       if (REG_P (parm_rtx))
-	 {
-	   for (reg = 0; reg < REG_NREGS (parm_rtx); reg++)
-	     if (!call_used_or_fixed_reg_p (reg + REGNO (parm_rtx)))
-	       return true;
-	 }
+      if (REG_P (parm_rtx))
+	{
+	  int size = s390_function_arg_size (arg.mode, arg.type);
+	  int nregs = (size + UNITS_PER_LONG - 1) / UNITS_PER_LONG;
 
-       if (GET_CODE (parm_rtx) == PARALLEL)
-	 {
-	   int i;
+	  for (reg = 0; reg < nregs; reg++)
+	    if (!call_used_or_fixed_reg_p (reg + REGNO (parm_rtx)))
+	      return true;
+	}
+      else if (GET_CODE (parm_rtx) == PARALLEL)
+	{
+	  int i;
 
-	   for (i = 0; i < XVECLEN (parm_rtx, 0); i++)
-	     {
-	       rtx r = XEXP (XVECEXP (parm_rtx, 0, i), 0);
+	  for (i = 0; i < XVECLEN (parm_rtx, 0); i++)
+	    {
+	      rtx r = XEXP (XVECEXP (parm_rtx, 0, i), 0);
 
-	       gcc_assert (REG_P (r));
-
-	       for (reg = 0; reg < REG_NREGS (r); reg++)
-		 if (!call_used_or_fixed_reg_p (reg + REGNO (r)))
-		   return true;
-	     }
-	 }
+	      gcc_assert (REG_P (r));
+	      gcc_assert (REG_NREGS (r) == 1);
 
+	      if (!call_used_or_fixed_reg_p (REGNO (r)))
+		return true;
+	    }
+	}
     }
   return false;
 }

gcc/testsuite/gcc.target/s390/pr106355-1.c

@@ -0,0 +1,42 @@
+/* { dg-do compile } */
+/* { dg-options "-foptimize-sibling-calls" } */
+/* { dg-final { scan-assembler {brasl\t%r\d+,bar4} } } */
+/* { dg-final { scan-assembler {brasl\t%r\d+,bar8} } } */
+
+/* Parameter E is passed in GPR 6 which is call-saved which prohibits
+   sibling call optimization.  This must hold true also if the mode of the
+   parameter is BLKmode.  */
+
+/* 4 byte */
+
+typedef struct
+{
+  char x;
+  char y[3];
+} t4;
+
+extern t4 e4;
+
+extern void bar4 (int a, int b, int c, int d, t4 e4);
+
+void foo4 (int a, int b, int c, int d)
+{
+  bar4 (a, b, c, d, e4);
+}
+
+/* 8 byte */
+
+typedef struct
+{
+  short x;
+  char y[6];
+} t8;
+
+extern t8 e8;
+
+extern void bar8 (int a, int b, int c, int d, t8 e8);
+
+void foo8 (int a, int b, int c, int d)
+{
+  bar8 (a, b, c, d, e8);
+}

gcc/testsuite/gcc.target/s390/pr106355-2.c

@@ -0,0 +1,8 @@
+/* { dg-do compile { target { s390-*-* } } } */
+/* { dg-options "-foptimize-sibling-calls -mzarch" } */
+/* { dg-final { scan-assembler {brasl\t%r\d+,bar} } } */
+
+/* This tests function s390_call_saved_register_used where
+   GET_CODE (parm_rtx) == PARALLEL holds.  */
+
+#include "pr106355.h"

gcc/testsuite/gcc.target/s390/pr106355-3.c

@@ -0,0 +1,8 @@
+/* { dg-do compile { target { s390-*-* } } } */
+/* { dg-options "-foptimize-sibling-calls -mesa" } */
+/* { dg-final { scan-assembler {brasl\t%r\d+,bar} } } */
+
+/* This tests function s390_call_saved_register_used where
+   REG_P (parm_rtx) and nregs == 2 holds.  */
+
+#include "pr106355.h"

gcc/testsuite/gcc.target/s390/pr106355.h

@@ -0,0 +1,18 @@
+/* For the S/390 ABI parameter D is passed in GPR 5 and 6 and the latter is
+   call-saved which prohibits sibling call optimization.  This must hold true
+   also if the mode of the parameter is BLKmode.  */
+
+typedef struct
+{
+  short x;
+  char y[6];
+} t;
+
+extern t d;
+
+extern void bar (int a, int b, int c, t d);
+
+void foo (int a, int b, int c)
+{
+  bar (a, b, c, d);
+}