On Tue, Feb 27, 2024 at 01:09:09PM +0100, Jakub Jelinek wrote:
> So, IMHO either revert the changes altogether, or guard on -mcmodel=kernel
> (but talk to kernel people on linux-toolchains if that is what they actually
> want).
Here is a patch which guards this by non-default option, so kernel and other
users can choose if they want this or not. On top of the PR114116 patch.
Only lightly tested so far.
2024-02-27 Jakub Jelinek <ja...@redhat.com>
PR target/38534
* config/i386/i386.opt (mnoreturn-no-callee-saved-registers): New
option.
* config/i386/i386-options.cc (ix86_set_func_type): Don't use
TYPE_NO_CALLEE_SAVED_REGISTERS_EXCEPT_BP unless
ix86_noreturn_no_callee_saved_registers is enabled.
* doc/invoke.texi (-mnoreturn-no-callee-saved-registers): Document.
* gcc.target/i386/pr38534-1.c: Add -mnoreturn-no-callee-saved-registers
to dg-options.
* gcc.target/i386/pr38534-2.c: Likewise.
* gcc.target/i386/pr38534-3.c: Likewise.
* gcc.target/i386/pr38534-4.c: Likewise.
* gcc.target/i386/pr38534-5.c: Likewise.
* gcc.target/i386/pr38534-6.c: Likewise.
* gcc.target/i386/pr114097-1.c: Likewise.
* gcc.target/i386/stack-check-17.c: Likewise.
--- gcc/config/i386/i386.opt.jj 2024-01-10 12:19:07.694681189 +0100
+++ gcc/config/i386/i386.opt 2024-02-27 14:18:34.439240869 +0100
@@ -659,6 +659,10 @@ mstore-max=
Target RejectNegative Joined Var(ix86_store_max) Enum(prefer_vector_width)
Init(PVW_NONE) Save
Maximum number of bits that can be stored to memory efficiently.
+mnoreturn-no-callee-saved-registers
+Target Var(ix86_noreturn_no_callee_saved_registers)
+Optimize noreturn functions by not saving callee-saved registers used in the
function.
+
;; ISA support
m32
--- gcc/config/i386/i386-options.cc.jj 2024-02-27 14:20:59.972228314 +0100
+++ gcc/config/i386/i386-options.cc 2024-02-27 14:23:26.042208182 +0100
@@ -3384,7 +3384,8 @@ ix86_set_func_type (tree fndecl)
{
/* No need to save and restore callee-saved registers for a noreturn
function with nothrow or compiled with -fno-exceptions unless when
- compiling with -O0 or -Og. So that backtrace works for those at least
+ compiling with -O0 or -Og, except that it interferes with debugging
+ of callers. So that backtrace works for those at least
in most cases, save the bp register if it is used, because it often
is used in callers to compute CFA.
@@ -3401,7 +3402,8 @@ ix86_set_func_type (tree fndecl)
if (lookup_attribute ("no_callee_saved_registers",
TYPE_ATTRIBUTES (TREE_TYPE (fndecl))))
no_callee_saved_registers = TYPE_NO_CALLEE_SAVED_REGISTERS;
- else if (TREE_THIS_VOLATILE (fndecl)
+ else if (ix86_noreturn_no_callee_saved_registers
+ && TREE_THIS_VOLATILE (fndecl)
&& optimize
&& !optimize_debug
&& (TREE_NOTHROW (fndecl) || !flag_exceptions)
--- gcc/doc/invoke.texi.jj 2024-02-23 11:34:34.278287553 +0100
+++ gcc/doc/invoke.texi 2024-02-27 14:29:18.071339182 +0100
@@ -1450,6 +1450,7 @@ See RS/6000 and PowerPC Options.
-mvzeroupper -mprefer-avx128 -mprefer-vector-width=@var{opt}
-mpartial-vector-fp-math
-mmove-max=@var{bits} -mstore-max=@var{bits}
+-mnoreturn-no-callee-saved-registers
-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx
-mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl
-mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes
@@ -35376,6 +35377,15 @@ Prefer 256-bit vector width for instruct
Prefer 512-bit vector width for instructions.
@end table
+@opindex mnoreturn-no-callee-saved-registers
+@item -mnoreturn-no-callee-saved-registers
+This option optimizes functions with @code{noreturn} attribute or
+@code{_Noreturn} specifier by not saving in the function prologue callee-saved
+registers which are used in the function (except for the @code{BP}
+register). This option can interfere with debugging of the caller of the
+@code{noreturn} function or any function further up in the call stack, so it
+is not enabled by default.
+
@opindex mcx16
@item -mcx16
This option enables GCC to generate @code{CMPXCHG16B} instructions in 64-bit
--- gcc/testsuite/gcc.target/i386/pr38534-1.c.jj 2024-02-27
14:21:00.385222600 +0100
+++ gcc/testsuite/gcc.target/i386/pr38534-1.c 2024-02-27 15:39:44.687716915
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer" } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer -mnoreturn-no-callee-saved-registers" } */
#define ARRAY_SIZE 256
--- gcc/testsuite/gcc.target/i386/pr38534-2.c.jj 2024-02-27
14:21:00.385222600 +0100
+++ gcc/testsuite/gcc.target/i386/pr38534-2.c 2024-02-27 15:39:51.569621585
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer" } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer -mnoreturn-no-callee-saved-registers" } */
extern void bar (void) __attribute__ ((no_callee_saved_registers));
extern void fn (void) __attribute__ ((noreturn));
--- gcc/testsuite/gcc.target/i386/pr38534-3.c.jj 2024-02-27
14:21:00.385222600 +0100
+++ gcc/testsuite/gcc.target/i386/pr38534-3.c 2024-02-27 15:39:57.420540547
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer" } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer -mnoreturn-no-callee-saved-registers" } */
typedef void (*fn_t) (void) __attribute__ ((no_callee_saved_registers));
extern fn_t bar;
--- gcc/testsuite/gcc.target/i386/pr38534-4.c.jj 2024-02-27
14:21:00.385222600 +0100
+++ gcc/testsuite/gcc.target/i386/pr38534-4.c 2024-02-27 15:40:08.185391436
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer" } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer -mnoreturn-no-callee-saved-registers" } */
typedef void (*fn_t) (void) __attribute__ ((no_callee_saved_registers));
extern void fn (void) __attribute__ ((noreturn));
--- gcc/testsuite/gcc.target/i386/pr38534-5.c.jj 2024-01-30
08:45:06.904842201 +0100
+++ gcc/testsuite/gcc.target/i386/pr38534-5.c 2024-02-27 15:49:17.382784286
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O0 -mtune-ctrl=^prologue_using_move,^epilogue_using_move" }
*/
+/* { dg-options "-O0 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-mnoreturn-no-callee-saved-registers" } */
#define ARRAY_SIZE 256
--- gcc/testsuite/gcc.target/i386/pr38534-6.c.jj 2024-01-30
08:45:06.904842201 +0100
+++ gcc/testsuite/gcc.target/i386/pr38534-6.c 2024-02-27 15:49:32.123580145
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move" }
*/
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-mnoreturn-no-callee-saved-registers" } */
#define ARRAY_SIZE 256
--- gcc/testsuite/gcc.target/i386/pr114097-1.c.jj 2024-02-27
14:21:00.386222586 +0100
+++ gcc/testsuite/gcc.target/i386/pr114097-1.c 2024-02-27 15:41:12.758496992
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer" } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move
-fomit-frame-pointer -mnoreturn-no-callee-saved-registers" } */
#define ARRAY_SIZE 256
--- gcc/testsuite/gcc.target/i386/stack-check-17.c.jj 2024-02-27
14:21:00.386222586 +0100
+++ gcc/testsuite/gcc.target/i386/stack-check-17.c 2024-02-27
15:41:42.269088224 +0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -fstack-clash-protection -mtune=generic
-fomit-frame-pointer" } */
+/* { dg-options "-O2 -fstack-clash-protection -mtune=generic
-fomit-frame-pointer -mnoreturn-no-callee-saved-registers" } */
/* { dg-require-effective-target supports_stack_clash_protection } */
/* { dg-skip-if "" { *-*-* } { "-fstack-protector*" } { "" } } */
Jakub
