(expand_expr): Use a smaller alignment when reading from a field

with a variable offset.

From-SVN: r6054

diff --git a/gcc/expr.c b/gcc/expr.c
index 4d99bca4937d6bac2a8ff1a010b72ffe200f40e9..70636b6401c127bcd11f75f46e1028599520767a 100644 (file)
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4314,6 +4314,7 @@ expand_expr (exp, target, tmode, modifier)
        int volatilep = 0;
        tree tem = get_inner_reference (exp, &bitsize, &bitpos, &offset,
                                        &mode1, &unsignedp, &volatilep);
+       int alignment;
 
        /* If we got back the original object, something is wrong.  Perhaps
           we are evaluating an expression too early.  In any event, don't
@@ -4337,6 +4338,7 @@ expand_expr (exp, target, tmode, modifier)
              op0 = validize_mem (force_const_mem (mode, op0));
          }
 
+       alignment = TYPE_ALIGN (TREE_TYPE (tem)) / BITS_PER_UNIT;
        if (offset != 0)
          {
            rtx offset_rtx = expand_expr (offset, NULL_RTX, VOIDmode, 0);
@@ -4346,6 +4348,14 @@ expand_expr (exp, target, tmode, modifier)
            op0 = change_address (op0, VOIDmode,
                                  gen_rtx (PLUS, Pmode, XEXP (op0, 0),
                                           force_reg (Pmode, offset_rtx)));
+         /* If we have a variable offset, the known alignment
+            is only that of the innermost structure containing the field.
+            (Actually, we could sometimes do better by using the
+            size of an element of the innermost array, but no need.)  */
+         if (TREE_CODE (exp) == COMPONENT_REF
+             || TREE_CODE (exp) == BIT_FIELD_REF)
+           alignment = (TYPE_ALIGN (TREE_TYPE (TREE_OPERAND (exp, 0)))
+                        / BITS_PER_UNIT);
          }
 
        /* Don't forget about volatility even if this is a bitfield.  */
@@ -4382,7 +4392,7 @@ expand_expr (exp, target, tmode, modifier)
 
            op0 = extract_bit_field (validize_mem (op0), bitsize, bitpos,
                                     unsignedp, target, ext_mode, ext_mode,
-                                    TYPE_ALIGN (TREE_TYPE (tem)) / BITS_PER_UNIT,
+                                    alignment,
                                     int_size_in_bytes (TREE_TYPE (tem)));
            if (mode == BLKmode)
              {