I appear to have forgotten to cc gcc-patches, sorry about that.
There are currently three cases where we issue a warning when disabling
-mcall-ms2sysv-xlogues for a function, but I never added a proper
warning, so there's no mechanism for disabling it. This is something
that I meant to address sooner. I'm thinking that it's better to just
remove the warning entirely and document these cases, rather than adding
a new warning. Any thoughts?
These are the conditions:
* the use of -fsplit-stack,
* the use of static call chains (not sure if we can ever have that), and
* if the function calls __buildin_eh_return.
Some of these cases can likely be supported, but they are just on the
"not yet tested" list.
2017-06-11 Daniel Santos <daniel.san...@pobox.com
* config/i386/i386.c (warn_once_call_ms2sysv_xlogues): Remove.
(ix86_compute_frame_layout): Don't call warn_once_call_ms2sysv_xlogues.
(ix86_expand_call): Likewise.
Thanks,
Daniel
Signed-off-by: Daniel Santos <daniel.san...@pobox.com>
---
gcc/config/i386/i386.c | 26 +++-----------------------
gcc/doc/invoke.texi | 25 ++++++++++++++++++++-----
2 files changed, 23 insertions(+), 28 deletions(-)
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index d5c2d46bf5e..2dc6e53c765 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -12772,18 +12772,6 @@ ix86_builtin_setjmp_frame_value (void)
return stack_realign_fp ? hard_frame_pointer_rtx : virtual_stack_vars_rtx;
}
-/* Emits a warning for unsupported msabi to sysv pro/epilogues. */
-static void warn_once_call_ms2sysv_xlogues (const char *feature)
-{
- static bool warned_once = false;
- if (!warned_once)
- {
- warning (0, "-mcall-ms2sysv-xlogues is not compatible with %s",
- feature);
- warned_once = true;
- }
-}
-
/* When using -fsplit-stack, the allocation routines set a field in
the TCB to the bottom of the stack plus this much space, measured
in bytes. */
@@ -12814,18 +12802,10 @@ ix86_compute_frame_layout (void)
gcc_assert (TARGET_SSE);
gcc_assert (!ix86_using_red_zone ());
- if (crtl->calls_eh_return)
+ if (crtl->calls_eh_return || ix86_static_chain_on_stack)
{
gcc_assert (!reload_completed);
m->call_ms2sysv = false;
- warn_once_call_ms2sysv_xlogues ("__builtin_eh_return");
- }
-
- else if (ix86_static_chain_on_stack)
- {
- gcc_assert (!reload_completed);
- m->call_ms2sysv = false;
- warn_once_call_ms2sysv_xlogues ("static call chains");
}
/* Finally, compute which registers the stub will manage. */
@@ -29290,9 +29270,9 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1,
else if (ix86_function_ms_hook_prologue (current_function_decl))
;
- /* TODO: Cases not yet examined. */
+ /* TODO: Compatibility not yet examined. */
else if (flag_split_stack)
- warn_once_call_ms2sysv_xlogues ("-fsplit-stack");
+ ;
else
{
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c1168823af7..eec02b43a4f 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -25389,11 +25389,26 @@ using the function attributes @code{ms_abi} and
@code{sysv_abi}.
@opindex mno-call-ms2sysv-xlogues
Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a
System V ABI function must consider RSI, RDI and XMM6-15 as clobbered. By
-default, the code for saving and restoring these registers is emitted inline,
-resulting in fairly lengthy prologues and epilogues. Using
-@option{-mcall-ms2sysv-xlogues} emits prologues and epilogues that
-use stubs in the static portion of libgcc to perform these saves and restores,
-thus reducing function size at the cost of a few extra instructions.
+default, the instructions for saving and restoring these registers are emitted
+inline, resulting in fairly lengthy pro- and epilogues. Using
+@option{-mcall-ms2sysv-xlogues} emits pro- and epilogues that use stubs in the
+static portion of libgcc to perform these saves and restores, thus reducing
+function size at the cost of executing a few extra instructions. This cost is
+theoretically mitigated or eliminated by reduced instruction cache utilization,
+temporal locality of the stubs, and the stubs' use of MOV instructions over
+PUSH and POP.
+
+This option is not supported with SEH, so it is completely unavailable on
+Windows. It is also silently disabled if a function:
+
+@enumerate
+@item is built with @option{-mno-sse2} or @option{-fsplit-stack},
+@item has @code{__attribute__ ((ms_hook_prologue))}, or
+@item either throws an exception or explicitly calls
@code{__builtin_eh_return}.
+@end enumerate
+
+Support for @option{-fsplit-stack} and @code{__builtin_eh_return} may be
+added at some time in the future, but has not yet been tested.
@item -mtls-dialect=@var{type}
@opindex mtls-dialect
--
2.11.0
