[Committed] PR26977: Invalid paradoxical SUBREGs in emit_group_store

[Roger Sayle <roger at eyesopen dot com>]

The following patch should resolve PR middle-end/26977 which is a
bootstrap failure building Ada on IA-64 introduced by my recent fix
for PR17959.  It turns out that simplify_gen_subreg can sometimes
return NULL_RTX if it fails to produce a legitimate paradoxical SUBREG.
In the case of this failure, it doesn't like a paradoxical extension
from SFmode to TImode, even though we seem to be able to create an
insv instruction for the same mode combination.

The obvious patch below checks whether simplify_gen_subreg returns
a non-NULL rtx before performing the new optimization.

This patch has been tested on x86_64-unknown-linux-gnu, with a
full "make bootstrap", all default languages, and regression
tested with a top-level "make -k check" with no new failures.

Committed to mainline as revision 112626.
Many thanks to Andreas Schwab for his help investigating this.



2006-04-02  Roger Sayle  <roger@eyesopen.com>

	PR middle-end/26977
	* expr.c (emit_group_store): Check whether simplify_gen_subreg returns
	NULL_RTX, indicating it couldn't create a valid paradoxical subreg.


Index: expr.c
===================================================================
*** expr.c	(revision 112608)
--- expr.c	(working copy)
*************** emit_group_store (rtx orig_dst, rtx src,
*** 1945,1953 ****
  	    {
  	      temp = simplify_gen_subreg (outer, tmps[start],
  					  inner, bytepos);
! 	      emit_move_insn (dst, temp);
! 	      done = true;
! 	      start++;
  	    }
  	}

--- 1945,1956 ----
  	    {
  	      temp = simplify_gen_subreg (outer, tmps[start],
  					  inner, bytepos);
! 	      if (temp)
! 		{
! 		  emit_move_insn (dst, temp);
! 		  done = true;
! 		  start++;
! 		}
  	    }
  	}

*************** emit_group_store (rtx orig_dst, rtx src,
*** 1961,1969 ****
  	    {
  	      temp = simplify_gen_subreg (outer, tmps[finish - 1],
  					  inner, bytepos);
! 	      emit_move_insn (dst, temp);
! 	      done = true;
! 	      finish--;
  	    }
  	}

--- 1964,1975 ----
  	    {
  	      temp = simplify_gen_subreg (outer, tmps[finish - 1],
  					  inner, bytepos);
! 	      if (temp)
! 		{
! 		  emit_move_insn (dst, temp);
! 		  done = true;
! 		  finish--;
! 		}
  	    }
  	}


Roger
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