On Mon, Apr 18, 2011 at 12:56 AM, Eric Botcazou <ebotca...@adacore.com> wrote:
> Hi,
>
> this (partially) fixes the LTO bootstrap failure with Ada enabled on the
> mainline. The problem is an ICE whose origin is as follows:
> 1. during LTO stage, copy-prop eliminates a DECL_IN_CONSTANT_POOL variable
> from the GIMPLE IR, except for a reference in a GIMPLE_DEBUG statement
> (ADDR_EXPR of the variable is the debug value),
> 2. the variable is streamed out in the object file, as well as its associated
> varpool entry,
> 3. during WPA stage, both are streamed in, then reachability analysis is run
> and computes that the variable is unreachable so removes the varpool entry.
> As a consequence, when the variable is streamed out again, its initializer
> gets
> replaced with ERROR_MARK.
> 4. during LTRANS stage, the variable is again streamed in, with ERROR_MARK as
> initializer and this blows up when the GIMPLE_DEBUG statement is processed.
>
> So the root problem is in the reachability analysis during the WPA stage but,
> as pointed out by Jakub, this is so by design for GIMPLE_DEBUG statements.
>
> There are already cases for which expand_debug_expr simply gives up:
>
> case VAR_DECL:
> case PARM_DECL:
> case FUNCTION_DECL:
> case LABEL_DECL:
> case CONST_DECL:
> case RESULT_DECL:
> op0 = DECL_RTL_IF_SET (exp);
>
> /* This decl was probably optimized away. */
> if (!op0)
> {
> if (TREE_CODE (exp) != VAR_DECL
> || DECL_EXTERNAL (exp)
> || !TREE_STATIC (exp)
> || !DECL_NAME (exp)
> || DECL_HARD_REGISTER (exp)
> || DECL_IN_CONSTANT_POOL (exp)
> || mode == VOIDmode)
> return NULL;
>
> the attached patch adds DECL_IN_CONSTANT_POOL to them. This makes it possible
> to eliminate the ICE (but LTO bootstrap still fails because of an unrelated
> ICE in dwarf2out.c later). OK for the mainline?
Ok.
I've run into similar issues when trying to do constant folding of initializers
on debug-stmts - sometimes they refer to optimized out vars which have
a error-mark initializer but the constant folding code then happily thinks
their initializer is zero, giving wrong debug info ...
Thanks,
Richard.
>
> 2011-04-17 Eric Botcazou <ebotca...@adacore.com>
>
> PR lto/48492
> * cfgexpand.c (expand_debug_expr) <VAR_DECL>: Return NULL for a
> DECL_IN_CONSTANT_POOL without RTL.
>
>
> --
> Eric Botcazou
>
