[backport from gcc-4.7/trunk ] Date: Wed, 2 Mar 2011 18:44:18 +0100 From: Jakub Jelinek Subject: [4.7 PATCH] Decrease size of DW_AT_bit_offset on little-endian targets (PR debug/47946) List-Archive: Hi! DW_AT_bit_offset on little-endian targets often has negative values, if we encode it as add_AT_unsigned, it needs DW_FORM_data8 for HWI 64 and DW_FORM_data4 for HWI 32. But the numbers are usually small negative values, so encoding them using DW_FORM_sdata is much more compact. Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for 4.7? DWARF4 obsoletes DW_AT_bit_offset with DW_AT_data_bit_offset, but this patch doesn't try to change it for -gdwarf-4, that would be more work (and most probably gdb doesn't handle it yet either). gcc/ 2011-03-14 Jakub Jelinek PR debug/47946 * dwarf2out.c (add_bit_offset_attribute): If bit_offset is negative, emit it as add_AT_int instead of add_AT_unsigned. --- gcc-4.6-20110312/gcc/dwarf2out.c.~1~ 2011-03-04 15:19:19.000000000 +0100 +++ gcc-4.6-20110312/gcc/dwarf2out.c 2011-03-16 20:35:56.000000000 +0100 @@ -1,6 +1,6 @@ /* Output Dwarf2 format symbol table information from GCC. Copyright (C) 1992, 1993, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, - 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 + 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc. Contributed by Gary Funck (gary@intrepid.com). Derived from DWARF 1 implementation of Ron Guilmette (rfg@monkeys.com). @@ -17685,7 +17685,7 @@ add_bit_offset_attribute (dw_die_ref die HOST_WIDE_INT bitpos_int; HOST_WIDE_INT highest_order_object_bit_offset; HOST_WIDE_INT highest_order_field_bit_offset; - HOST_WIDE_INT unsigned bit_offset; + HOST_WIDE_INT bit_offset; /* Must be a field and a bit field. */ gcc_assert (type && TREE_CODE (decl) == FIELD_DECL); @@ -17718,7 +17718,10 @@ add_bit_offset_attribute (dw_die_ref die ? highest_order_object_bit_offset - highest_order_field_bit_offset : highest_order_field_bit_offset - highest_order_object_bit_offset); - add_AT_unsigned (die, DW_AT_bit_offset, bit_offset); + if (bit_offset < 0) + add_AT_int (die, DW_AT_bit_offset, bit_offset); + else + add_AT_unsigned (die, DW_AT_bit_offset, (unsigned HOST_WIDE_INT) bit_offset); } /* For a FIELD_DECL node which represents a bit field, output an attribute