From 28b039e3025d95c870e134eb24668ef0370175cc Mon Sep 17 00:00:00 2001 From: Richard Stallman Date: Sat, 26 Sep 1992 20:40:25 +0000 Subject: [PATCH] (location_attribute): If DECL_RTL looks like (MEM pseudo), treat that variable as optimized away. From-SVN: r2253 --- gcc/dwarfout.c | 40 +++++++++++++++++++++++++++++++++------- 1 file changed, 33 insertions(+), 7 deletions(-) diff --git a/gcc/dwarfout.c b/gcc/dwarfout.c index c9d5725..d282329 100644 --- a/gcc/dwarfout.c +++ b/gcc/dwarfout.c @@ -1478,7 +1478,19 @@ output_mem_loc_descriptor (rtl) be referred to as a "base register". This distinction is not based in any way upon what category of register the hardware believes the given register belongs to. This is strictly - Dwarf terminology we're dealing with here. */ + Dwarf terminology we're dealing with here. + + Note that in cases where the location of a memory-resident data + object could be expressed as: + + OP_ADD (OP_BASEREG (basereg), OP_CONST (0)) + + the actual DWARF location descriptor that we generate may just + be OP_BASEREG (basereg). This may look deceptively like the + object in question was allocated to a register (rather than + in memory) so DWARF consumers need to be aware of the subtle + distinction between OP_REG and OP_BASEREG. + */ ASM_OUTPUT_DWARF_STACK_OP (asm_out_file, OP_BASEREG); ASM_OUTPUT_DWARF_DATA4 (asm_out_file, @@ -1877,13 +1889,27 @@ location_attribute (rtl) /* Handle a special case. If we are about to output a location descriptor for a variable or parameter which has been optimized out of existence, don't do that. Instead we output a zero-length location descriptor - value as part of the location attribute. Note that we cannot simply - suppress the entire location attribute, because the absence of a - location attribute in certain kinds of DIEs is used to indicate some- - thing entirely different... i.e. that the DIE represents an object - declaration, but not a definition. So sayeth the PLSIG. */ + value as part of the location attribute. + + A variable which has been optimized out of existance will have a + DECL_RTL value which denotes a pseudo-reg. + + Currently, in some rare cases, variables can have DECL_RTL values + which look like (MEM (REG pseudo-reg#)). These cases are due to + bugs elsewhere in the compiler. We treat such cases + as if the variable(s) in question had been optimized out of existance. + + Note that in all cases where we wish to express the fact that a + variable has been optimized out of existance, we do not simply + suppress the generation of the entire location attribute because + the absence of a location attribute in certain kinds of DIEs is + used to indicate something else entirely... i.e. that the DIE + represents an object declaration, but not a definition. So sayeth + the PLSIG. + */ - if (! is_pseudo_reg (rtl)) + if (! is_pseudo_reg (rtl) + && (GET_CODE (rtl) != MEM || ! is_pseudo_reg (XEXP (rtl, 0)))) output_loc_descriptor (eliminate_regs (rtl, 0, NULL_RTX)); ASM_OUTPUT_LABEL (asm_out_file, end_label); -- 2.7.4