stor-layout.c (finish_bitfield_representative): Fallback to conservative maximum size if the padding up to the next field...

2012-03-20  Richard Guenther  <rguenther@suse.de>

	* stor-layout.c (finish_bitfield_representative): Fallback
	to conservative maximum size if the padding up to the next
	field cannot be computed as a constant.
	(finish_bitfield_layout): If we cannot compute the distance
	between the start of the bitfield representative and the
	bitfield member start a new representative.
	* expr.c (get_bit_range): The distance between the start of
	the bitfield representative and the bitfield member is zero
	if the field offsets are not constants.

	* gnat.dg/pack16.adb: New testcase.
	* gnat.dg/pack16_pkg.ads: Likewise.
	* gnat.dg/specs/pack8.ads: Likewise.
	* gnat.dg/specs/pack8_pkg.ads: Likewise.

From-SVN: r185563

gcc/ChangeLog

@@ -1,3 +1,15 @@
+2012-03-20  Richard Guenther  <rguenther@suse.de>
+
+	* stor-layout.c (finish_bitfield_representative): Fallback
+	to conservative maximum size if the padding up to the next
+	field cannot be computed as a constant.
+	(finish_bitfield_layout): If we cannot compute the distance
+	between the start of the bitfield representative and the
+	bitfield member start a new representative.
+	* expr.c (get_bit_range): The distance between the start of
+	the bitfield representative and the bitfield member is zero
+	if the field offsets are not constants.
+
 2012-03-20  Tristan Gingold  <gingold@adacore.com>
 
 	* tree.h (enum size_type_kind): Add stk_ prefix to constants,

gcc/expr.c

@@ -4452,7 +4452,7 @@ get_bit_range (unsigned HOST_WIDE_INT *bitstart,
 	       HOST_WIDE_INT bitpos)
 {
   unsigned HOST_WIDE_INT bitoffset;
-  tree field, repr, offset;
+  tree field, repr;
 
   gcc_assert (TREE_CODE (exp) == COMPONENT_REF);
 
@@ -4467,12 +4467,17 @@ get_bit_range (unsigned HOST_WIDE_INT *bitstart,
     }
 
   /* Compute the adjustment to bitpos from the offset of the field
-     relative to the representative.  */
-  offset = size_diffop (DECL_FIELD_OFFSET (field),
-			DECL_FIELD_OFFSET (repr));
-  bitoffset = (tree_low_cst (offset, 1) * BITS_PER_UNIT
-	       + tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1)
-	       - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
+     relative to the representative.  DECL_FIELD_OFFSET of field and
+     repr are the same by construction if they are not constants,
+     see finish_bitfield_layout.  */
+  if (host_integerp (DECL_FIELD_OFFSET (field), 1)
+      && host_integerp (DECL_FIELD_OFFSET (repr), 1))
+    bitoffset = (tree_low_cst (DECL_FIELD_OFFSET (field), 1)
+		 - tree_low_cst (DECL_FIELD_OFFSET (repr), 1)) * BITS_PER_UNIT;
+  else
+    bitoffset = 0;
+  bitoffset += (tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1)
+		- tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
 
   *bitstart = bitpos - bitoffset;
   *bitend = *bitstart + tree_low_cst (DECL_SIZE (repr), 1) - 1;

gcc/stor-layout.c

@@ -1781,10 +1781,17 @@ finish_bitfield_representative (tree repr, tree field)
 	return;
       maxsize = size_diffop (DECL_FIELD_OFFSET (nextf),
 			     DECL_FIELD_OFFSET (repr));
-      gcc_assert (host_integerp (maxsize, 1));
-      maxbitsize = (tree_low_cst (maxsize, 1) * BITS_PER_UNIT
-		    + tree_low_cst (DECL_FIELD_BIT_OFFSET (nextf), 1)
-		    - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
+      if (host_integerp (maxsize, 1))
+	{
+	  maxbitsize = (tree_low_cst (maxsize, 1) * BITS_PER_UNIT
+			+ tree_low_cst (DECL_FIELD_BIT_OFFSET (nextf), 1)
+			- tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
+	  /* If the group ends within a bitfield nextf does not need to be
+	     aligned to BITS_PER_UNIT.  Thus round up.  */
+	  maxbitsize = (maxbitsize + BITS_PER_UNIT - 1) & ~(BITS_PER_UNIT - 1);
+	}
+      else
+	maxbitsize = bitsize;
     }
   else
     {
@@ -1888,6 +1895,8 @@ finish_bitfield_layout (record_layout_info rli)
 	}
       else if (DECL_BIT_FIELD_TYPE (field))
 	{
+	  gcc_assert (repr != NULL_TREE);
+
 	  /* Zero-size bitfields finish off a representative and
 	     do not have a representative themselves.  This is
 	     required by the C++ memory model.  */
@@ -1896,6 +1905,24 @@ finish_bitfield_layout (record_layout_info rli)
 	      finish_bitfield_representative (repr, prev);
 	      repr = NULL_TREE;
 	    }
+
+	  /* We assume that either DECL_FIELD_OFFSET of the representative
+	     and each bitfield member is a constant or they are equal.
+	     This is because we need to be able to compute the bit-offset
+	     of each field relative to the representative in get_bit_range
+	     during RTL expansion.
+	     If these constraints are not met, simply force a new
+	     representative to be generated.  That will at most
+	     generate worse code but still maintain correctness with
+	     respect to the C++ memory model.  */
+	  else if (!((host_integerp (DECL_FIELD_OFFSET (repr), 1)
+		      && host_integerp (DECL_FIELD_OFFSET (field), 1))
+		     || operand_equal_p (DECL_FIELD_OFFSET (repr),
+					 DECL_FIELD_OFFSET (field), 0)))
+	    {
+	      finish_bitfield_representative (repr, prev);
+	      repr = start_bitfield_representative (field);
+	    }
 	}
       else
 	continue;

gcc/testsuite/ChangeLog

@@ -1,3 +1,10 @@
+2012-03-20  Richard Guenther  <rguenther@suse.de>
+
+	* gnat.dg/pack16.adb: New testcase.
+	* gnat.dg/pack16_pkg.ads: Likewise.
+	* gnat.dg/specs/pack8.ads: Likewise.
+	* gnat.dg/specs/pack8_pkg.ads: Likewise.
+
 2012-03-19  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* g++.dg/warn/Wuseless-cast.C: Extend.

gcc/testsuite/gnat.dg/pack16.adb

@@ -0,0 +1,26 @@
+-- { dg-do compile }
+-- { dg-options "-gnatws" }
+
+with Pack16_Pkg; use Pack16_Pkg;
+
+procedure Pack16 is
+
+   type Sample_Table_T is array (1 .. N) of Integer;
+
+   type Clock_T is record
+      N_Ticks  : Integer := 0;
+   end record;
+
+   type Sampling_Descriptor_T is record
+      Values : Sample_Table_T;
+      Valid  : Boolean;
+      Tstamp : Clock_T;
+   end record;
+
+   pragma Pack (Sampling_Descriptor_T);
+
+   Sampling_Data : Sampling_Descriptor_T;
+
+begin
+   null;
+end;

gcc/testsuite/gnat.dg/pack16_pkg.ads

@@ -0,0 +1,5 @@
+package Pack16_Pkg is
+
+   N : Natural := 16;
+
+end Pack16_Pkg;

gcc/testsuite/gnat.dg/specs/pack8.ads

@@ -0,0 +1,19 @@
+with Pack8_Pkg;
+
+package Pack8 is
+
+   subtype Index_Type is Integer range 1 .. Pack8_Pkg.N;
+
+   subtype Str is String( Index_Type);
+
+   subtype Str2 is String (1 .. 11);
+
+   type Rec is record
+      S1 : Str;
+      S2 : Str;
+      B  : Boolean;
+      S3 : Str2;
+   end record;
+   pragma Pack (Rec);
+
+end Pack8;

gcc/testsuite/gnat.dg/specs/pack8_pkg.ads

@@ -0,0 +1,5 @@
+package Pack8_Pkg is
+
+   N : Natural := 1;
+
+end Pack8_Pkg;