Incorrect code due to indirect tail call of varargs function with hard float ABI

[Kugan]

Following testcase fails on ARM (from
https://bugs.linaro.org/show_bug.cgi?id=1900).

__attribute__ ((noinline))
double direct(int x, ...)
{
  return x*x;
}

__attribute__ ((noinline))
double broken(double (*indirect)(int x, ...), int v)
{
  return indirect(v);
}

int main ()
{
  double d1, d2;
  int i = 2;
  d1 = broken (direct, i);
  if (d1 != i*i)
    {
      __builtin_abort ();
    }
  return 0;
}


Please note that we have a sibcall from "broken" to "indirect".

"direct" is variadic function so it is conforming to AAPCS base standard.

"broken" is a non-variadic function and will return the value in
floating point register for TARGET_HARD_FLOAT. Thus we should not be
doing sibcall here.

Attached patch fixes this. Bootstrap and regression testing is ongoing.
Is this OK if no issues with the testing?

Thanks,
Kugan

gcc/ChangeLog:

2015-11-17  Kugan Vivekanandarajah  <kug...@linaro.org>

        * config/arm/arm.c (arm_function_ok_for_sibcall): Disable sibcall to
        indirect function when TARGET_HARD_FLOAT.

gcc/testsuite/ChangeLog:

2015-11-17  Kugan Vivekanandarajah  <kug...@linaro.org>

        * gcc.target/arm/variadic_sibcall.c: New test.


diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index a379121..8b560bc 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -6681,6 +6681,12 @@ arm_function_ok_for_sibcall (tree decl, tree exp)
         register.  */
       rtx a, b;
 
+      /* When it is an indirect call (i.e, decl == NULL), it could be
+        returning its result in a VFP or could be a variadic function.
+        Thus return false.  */
+      if (!decl && TARGET_HARD_FLOAT)
+       return false;
+
       a = arm_function_value (TREE_TYPE (exp), decl, false);
       b = arm_function_value (TREE_TYPE (DECL_RESULT (cfun->decl)),
                              cfun->decl, false);
diff --git a/gcc/testsuite/gcc.target/arm/variadic_sibcall.c 
b/gcc/testsuite/gcc.target/arm/variadic_sibcall.c
index e69de29..86f07fe 100644
--- a/gcc/testsuite/gcc.target/arm/variadic_sibcall.c
+++ b/gcc/testsuite/gcc.target/arm/variadic_sibcall.c
@@ -0,0 +1,27 @@
+/* { dg-do run }  */
+/* { dg-options "-O2" } */
+
+__attribute__ ((noinline))
+double direct(int x, ...)
+{
+  return x*x;
+}
+
+__attribute__ ((noinline))
+double broken(double (*indirect)(int x, ...), int v)
+{
+  return indirect(v);
+}
+
+int main ()
+{
+  double d1, d2;
+  int i = 2;
+  d1 = broken (direct, i);
+  if (d1 != i*i)
+    {
+      __builtin_abort ();
+    }
+  return 0;
+}
+