rs6000: mark tieable between INT and FLOAT

Hi,

During discussing/review patches in maillist, we find more modes are
tieable, e.g. DI<->DF.  With some discussion, I drafted this patch
to mark more tieable modes.

Bootstrap and regtest pass on ppc64{,le}.
Is this ok for trunk?

BR,
Jeff (Jiufu)

gcc/ChangeLog:

	* config/rs6000/rs6000.cc (rs6000_modes_tieable_p): Mark more tieable
	modes.

gcc/testsuite/ChangeLog:

	* g++.target/powerpc/pr102024.C: Updated.

gcc/config/rs6000/rs6000.cc

@@ -1968,6 +1968,15 @@ rs6000_modes_tieable_p (machine_mode mode1, machine_mode mode2)
   if (ALTIVEC_OR_VSX_VECTOR_MODE (mode2))
     return false;
 
+  /* SFmode format (IEEE DP) in register would not as required,
+     So SFmode is restrict here.  */
+  if (GET_MODE_CLASS (mode1) == MODE_FLOAT
+      && GET_MODE_CLASS (mode2) == MODE_INT)
+    return GET_MODE_SIZE (mode2) == UNITS_PER_FP_WORD && mode1 != SFmode;
+  if (GET_MODE_CLASS (mode1) == MODE_INT
+      && GET_MODE_CLASS (mode2) == MODE_FLOAT)
+    return GET_MODE_SIZE (mode1) == UNITS_PER_FP_WORD && mode2 != SFmode;
+
   if (SCALAR_FLOAT_MODE_P (mode1))
     return SCALAR_FLOAT_MODE_P (mode2);
   if (SCALAR_FLOAT_MODE_P (mode2))

gcc/testsuite/g++.target/powerpc/pr102024.C

@@ -5,7 +5,8 @@
 // Test that a zero-width bit field in an otherwise homogeneous aggregate
 // generates a psabi warning and passes arguments in GPRs.
 
-// { dg-final { scan-assembler-times {\mstd\M} 4 } }
+// { dg-final { scan-assembler-times {\mmtvsrd\M} 4 { target has_arch_pwr8 } } }
+// { dg-final { scan-assembler-times {\mstd\M} 4 { target { ! has_arch_pwr8 } } } }
 
 struct a_thing
 {