rs6000: Use SAVE_MULTIPLE only if we restore what it saves (PR80938)

We can have SAVE_MULTIPLE while we do not have REST_MULTIPLE.  If the
inline restore does not restore all registers, the CFI for the save
and restore can conflict if things are shrink-wrapped.

We could restore all registers that are saved (not ideal), or emit
the CFI notes to say we did (which will work fine, but is also not
so great); instead, let's not save the registers that are unused.


	PR target/80938
	* config/rs6000/rs6000.c (rs6000_savres_strategy): Don't use
	SAVE_MULTIPLE if not all the registers that saves, should be saved.

From-SVN: r251005

gcc/ChangeLog

+2017-08-09  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR target/80938
+	* config/rs6000/rs6000.c (rs6000_savres_strategy): Don't use
+	SAVE_MULTIPLE if not all the registers that saves, should be saved.
+
 2017-08-09  Jim Wilson  <jim.wilson@linaro.org>
 
 	* config/aarch64/aarch64-cores.def (falkor): Use falkor pipeline.

gcc/config/rs6000/rs6000.c

@@ -24431,6 +24431,21 @@ rs6000_savres_strategy (rs6000_stack_t *info,
   else if (!lr_save_p && info->first_gp_reg_save > 29)
     strategy |= SAVE_INLINE_GPRS | REST_INLINE_GPRS;
 
+  /* We can only use save multiple if we need to save all the registers from
+     first_gp_reg_save.  Otherwise, the CFI gets messed up (we save some
+     register we do not restore).  */
+  if (strategy & SAVE_MULTIPLE)
+    {
+      int i;
+
+      for (i = info->first_gp_reg_save; i < 32; i++)
+	if (fixed_reg_p (i) || !save_reg_p (i))
+	  {
+	    strategy &= ~SAVE_MULTIPLE;
+	    break;
+	  }
+    }
+
   /* We can only use load multiple or the out-of-line routines to
      restore gprs if we've saved all the registers from
      first_gp_reg_save.  Otherwise, we risk loading garbage.