[PATCH] Fix PR71055

[PATCH] Fix PR71055

[Richard Biener]

The following fixes PR71055.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.

Richard.

2016-05-11  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/71055
	* tree-ssa-sccvn.c (vn_reference_lookup_3): When native-interpreting
	sth with precision not equal to access size verify we don't chop
	off bits.

	* gcc.dg/torture/pr71055.c: New testcase.

Index: gcc/tree-ssa-sccvn.c
===================================================================
*** gcc/tree-ssa-sccvn.c	(revision 236069)
--- gcc/tree-ssa-sccvn.c	(working copy)
*************** vn_reference_lookup_3 (ao_ref *ref, tree
*** 1907,1920 ****
  				    buffer, sizeof (buffer));
  	  if (len > 0)
  	    {
! 	      tree val = native_interpret_expr (vr->type,
  						buffer
  						+ ((offset - offset2)
  						   / BITS_PER_UNIT),
  						ref->size / BITS_PER_UNIT);
  	      if (val)
  		return vn_reference_lookup_or_insert_for_pieces
! 		         (vuse, vr->set, vr->type, vr->operands, val);
  	    }
  	}
      }
--- 1950,1983 ----
  				    buffer, sizeof (buffer));
  	  if (len > 0)
  	    {
! 	      tree type = vr->type;
! 	      /* Make sure to interpret in a type that has a range
! 	         covering the whole access size.  */
! 	      if (INTEGRAL_TYPE_P (vr->type)
! 		  && ref->size != TYPE_PRECISION (vr->type))
! 		type = build_nonstandard_integer_type (ref->size,
! 						       TYPE_UNSIGNED (type));
! 	      tree val = native_interpret_expr (type,
  						buffer
  						+ ((offset - offset2)
  						   / BITS_PER_UNIT),
  						ref->size / BITS_PER_UNIT);
+ 	      /* If we chop off bits because the types precision doesn't
+ 		 match the memory access size this is ok when optimizing
+ 		 reads but not when called from the DSE code during
+ 		 elimination.  */
+ 	      if (val
+ 		  && type != vr->type)
+ 		{
+ 		  if (! int_fits_type_p (val, vr->type))
+ 		    val = NULL_TREE;
+ 		  else
+ 		    val = fold_convert (vr->type, val);
+ 		}
+ 
  	      if (val)
  		return vn_reference_lookup_or_insert_for_pieces
! 			 (vuse, vr->set, vr->type, vr->operands, val);
  	    }
  	}
      }
Index: gcc/testsuite/gcc.dg/torture/pr71055.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr71055.c	(revision 0)
--- gcc/testsuite/gcc.dg/torture/pr71055.c	(working copy)
***************
*** 0 ****
--- 1,18 ----
+ /* { dg-do run } */
+ 
+ extern void abort (void);
+ union U { int i; _Bool b; char c; };
+ void __attribute__((noinline,noclone))
+ foo (union U *u)
+ {
+   if (u->c != 0)
+     abort ();
+ }
+ int main()
+ {
+   union U u;
+   u.i = 10;
+   u.b = 0;
+   foo (&u);
+   return 0;
+ }