RFA: Fix REG_ARGS_SIZE handling when pushing TLS addresses
Richard Sandiford
richard.sandiford@linaro.org
Thu Dec 28 20:37:00 GMT 2017
Andreas Schwab <schwab@linux-m68k.org> writes:
> On Dez 23 2017, Richard Sandiford <richard.sandiford@linaro.org> wrote:
>> gcc/
>> * expr.c (fixup_args_size_notes): Check that any existing
>> REG_ARGS_SIZE notes are correct, and don't try to re-add them.
>> (emit_single_push_insn_1): Move stack_pointer_delta adjustment to...
>> (emit_single_push_insn): ...here.
>
> Successfully regtested on m68k-linux.
Thanks. Now also tested on aarch64-linux-gnu, x86_64-linux-gnu and
powerpc64-linux-gnu (not that that will give mucn coverage). Also
tested with a before-and-after comparison of testsuite output for
a range of targets. OK to install?
Richard
The new assert in add_args_size_note triggered for gcc.dg/tls/opt-3.c
and other on m68k. This looks like a pre-existing bug: if we pushed
a value that needs a call to something like __tls_get_addr, we ended
up with two different REG_ARGS_SIZE notes on the same instruction.
It seems to be OK for emit_single_push_insn to push something that
needs a call to __tls_get_addr:
/* We have to allow non-call_pop patterns for the case
of emit_single_push_insn of a TLS address. */
if (GET_CODE (pat) != PARALLEL)
return 0;
so I think the bug is in the way this is handled rather than the fact
that it occurs at all.
If we're pushing a value X that needs a call C to calculate, we'll
add REG_ARGS_SIZE notes to the pushes and pops for C as part of the
call sequence. Then emit_single_push_insn calls fixup_args_size_notes
on the whole push sequence (the calculation of X, including C,
and the push of X itself). This is where the double notes came from.
But emit_single_push_insn_1 adjusted stack_pointer_delta *before* the
push, so the notes added for C were relative to the situation after
the future push of X rather than before it.
Presumably this didn't matter in practice because the note added
second tended to trump the note added first. But code is allowed to
walk REG_NOTES without having to disregard secondary notes.
2017-12-23 Richard Sandiford <richard.sandiford@linaro.org>
gcc/
* expr.c (fixup_args_size_notes): Check that any existing
REG_ARGS_SIZE notes are correct, and don't try to re-add them.
(emit_single_push_insn_1): Move stack_pointer_delta adjustment to...
(emit_single_push_insn): ...here.
Index: gcc/expr.c
===================================================================
--- gcc/expr.c 2017-12-23 09:29:20.226338285 +0000
+++ gcc/expr.c 2017-12-23 09:29:45.783339673 +0000
@@ -4089,6 +4089,14 @@ fixup_args_size_notes (rtx_insn *prev, r
if (!NONDEBUG_INSN_P (insn))
continue;
+ /* We might have existing REG_ARGS_SIZE notes, e.g. when pushing
+ a call argument containing a TLS address that itself requires
+ a call to __tls_get_addr. The handling of stack_pointer_delta
+ in emit_single_push_insn is supposed to ensure that any such
+ notes are already correct. */
+ rtx note = find_reg_note (insn, REG_ARGS_SIZE, NULL_RTX);
+ gcc_assert (!note || known_eq (args_size, get_args_size (note)));
+
poly_int64 this_delta = find_args_size_adjust (insn);
if (known_eq (this_delta, 0))
{
@@ -4102,7 +4110,8 @@ fixup_args_size_notes (rtx_insn *prev, r
if (known_eq (this_delta, HOST_WIDE_INT_MIN))
saw_unknown = true;
- add_args_size_note (insn, args_size);
+ if (!note)
+ add_args_size_note (insn, args_size);
if (STACK_GROWS_DOWNWARD)
this_delta = -poly_uint64 (this_delta);
@@ -4126,7 +4135,6 @@ emit_single_push_insn_1 (machine_mode mo
rtx dest;
enum insn_code icode;
- stack_pointer_delta += PUSH_ROUNDING (GET_MODE_SIZE (mode));
/* If there is push pattern, use it. Otherwise try old way of throwing
MEM representing push operation to move expander. */
icode = optab_handler (push_optab, mode);
@@ -4213,6 +4221,14 @@ emit_single_push_insn (machine_mode mode
emit_single_push_insn_1 (mode, x, type);
+ /* Adjust stack_pointer_delta to describe the situation after the push
+ we just performed. Note that we must do this after the push rather
+ than before the push in case calculating X needs pushes and pops of
+ its own (e.g. if calling __tls_get_addr). The REG_ARGS_SIZE notes
+ for such pushes and pops must not include the effect of the future
+ push of X. */
+ stack_pointer_delta += PUSH_ROUNDING (GET_MODE_SIZE (mode));
+
last = get_last_insn ();
/* Notice the common case where we emitted exactly one insn. */
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