[Bug middle-end/21990] Wrong code for 4.0 and head: Reload clobbers the frame pointer by using it as spill register without recognizing the clobbering

[bjoern dot m dot haase at web dot de]

------- Additional Comments From bjoern dot m dot haase at web dot de  2005-09-04 10:35 -------
Indeed IMHO the problem stems from the patch:   
   
+2005-01-22  Roger Sayle  <roger@eyesopen.com>   
+   
+	PR middle-end/19378   
+	* config/avr/avr.c (avr_hard_regno_mode_ok): Rewrite.   
+   
   
IMO the problem stems from the change   
   
-  /* Reload can use r28:r29 for reload register and for frame pointer   
-   in one insn. It's wrong. We must disable it.  */   
-  if (mode != Pmode && reload_in_progress && frame_pointer_required_p ()   
-      && regno <= REG_Y && (regno + GET_MODE_SIZE (mode)) >= (REG_Y + 1))   
+  /* Otherwise disallow all regno/mode combinations that span r28:r29.  */   
+  if (regno <= (REG_Y + 1) && (regno + GET_MODE_SIZE (mode)) >= (REG_Y + 1))   
     return 0;   
   
Denis Chertykov's older version using "frame_pointer_required_p ()" has now   
vanished. A problem during register allocation has been removed by Roger  
Sayle's patch. However, the old frame pointer bug has been re-introduced.   
   
My suggestion is to use the following implementation. (according patch to   
today's head attached) This patch has passed regression tests on head without   
new regressions on head on the c-testsuite for compilation and simulator  
excecution for the atmega128.   
I also verified on an old snapshot that had exposed PR21990 that this patch  
resolves PR21990.  
  
I'll post this message also on gcc-patches.  
  
Yours,  
  
Bjoern  

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21990