There is no need to save callee-saved registers in noreturn functions
if they don't throw nor support exceptions. We can treat them the same
as functions with no_callee_saved_registers attribute.
Adjust stack-check-17.c for noreturn function which no longer saves any
registers.
With this change, __libc_start_main in glibc 2.39, which is a noreturn
function, is changed from
__libc_start_main:
endbr64
push %r15
push %r14
mov %rcx,%r14
push %r13
push %r12
push %rbp
mov %esi,%ebp
push %rbx
mov %rdx,%rbx
sub $0x28,%rsp
mov %rdi,(%rsp)
mov %fs:0x28,%rax
mov %rax,0x18(%rsp)
xor %eax,%eax
test %r9,%r9
to
__libc_start_main:
endbr64
sub $0x28,%rsp
mov %esi,%ebp
mov %rdx,%rbx
mov %rcx,%r14
mov %rdi,(%rsp)
mov %fs:0x28,%rax
mov %rax,0x18(%rsp)
xor %eax,%eax
test %r9,%r9
In Linux kernel 6.7.0 on x86-64, do_exit is changed from
do_exit:
endbr64
call <do_exit+0x9>
push %r15
push %r14
push %r13
push %r12
mov %rdi,%r12
push %rbp
push %rbx
mov %gs:0x0,%rbx
sub $0x28,%rsp
mov %gs:0x28,%rax
mov %rax,0x20(%rsp)
xor %eax,%eax
call *0x0(%rip) # <do_exit+0x39>
test $0x2,%ah
je <do_exit+0x8d3>
to
do_exit:
endbr64
call <do_exit+0x9>
sub $0x28,%rsp
mov %rdi,%r12
mov %gs:0x28,%rax
mov %rax,0x20(%rsp)
xor %eax,%eax
mov %gs:0x0,%rbx
call *0x0(%rip) # <do_exit+0x2f>
test $0x2,%ah
je <do_exit+0x8c9>
I compared GCC master branch bootstrap and test times on a slow machine
with 6.6 Linux kernels compiled with the original GCC 13 and the GCC 13
with the backported patch. The performance data isn't precise since the
measurements were done on different days with different GCC sources under
different 6.6 kernel versions.
GCC master branch build time in seconds:
before after improvement
30043.75user 30013.16user 0%
1274.85system 1243.72system 2.4%
GCC master branch test time in seconds (new tests added):
before after improvement
216035.90user 216547.51user 0
27365.51system 26658.54system 2.6%
gcc/
PR target/38534
* config/i386/i386-options.cc (ix86_set_func_type): Don't
save and restore callee saved registers for a noreturn function
with nothrow or compiled with -fno-exceptions.
gcc/testsuite/
PR target/38534
* gcc.target/i386/pr38534-1.c: New file.
* gcc.target/i386/pr38534-2.c: Likewise.
* gcc.target/i386/pr38534-3.c: Likewise.
* gcc.target/i386/pr38534-4.c: Likewise.
* gcc.target/i386/stack-check-17.c: Updated.
---
gcc/config/i386/i386-options.cc | 16 ++++++++++--
gcc/testsuite/gcc.target/i386/pr38534-1.c | 26 +++++++++++++++++++
gcc/testsuite/gcc.target/i386/pr38534-2.c | 18 +++++++++++++
gcc/testsuite/gcc.target/i386/pr38534-3.c | 19 ++++++++++++++
gcc/testsuite/gcc.target/i386/pr38534-4.c | 18 +++++++++++++
.../gcc.target/i386/stack-check-17.c | 19 +++++---------
6 files changed, 102 insertions(+), 14 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-1.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-2.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-3.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-4.c
diff --git a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc
index 0cdea30599e..f965568947c 100644
--- a/gcc/config/i386/i386-options.cc
+++ b/gcc/config/i386/i386-options.cc
@@ -3371,9 +3371,21 @@ ix86_simd_clone_adjust (struct cgraph_node *node)
static void
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.
+
+ NB: Don't use TREE_THIS_VOLATILE to check if this is a noreturn
+ function. The local-pure-const pass turns an interrupt function
+ into a noreturn function by setting TREE_THIS_VOLATILE. Normally
+ the local-pure-const pass is run after ix86_set_func_type is called.
+ When the local-pure-const pass is enabled for LTO, the interrupt
+ function is marked as noreturn in the IR output, which leads the
+ incompatible attribute error in LTO1. */
bool has_no_callee_saved_registers
- = lookup_attribute ("no_callee_saved_registers",
- TYPE_ATTRIBUTES (TREE_TYPE (fndecl)));
+ = (((TREE_NOTHROW (fndecl) || !flag_exceptions)
+ && lookup_attribute ("noreturn", DECL_ATTRIBUTES (fndecl)))
+ || lookup_attribute ("no_callee_saved_registers",
+ TYPE_ATTRIBUTES (TREE_TYPE (fndecl))));
if (cfun->machine->func_type == TYPE_UNKNOWN)
{
diff --git a/gcc/testsuite/gcc.target/i386/pr38534-1.c
b/gcc/testsuite/gcc.target/i386/pr38534-1.c
new file mode 100644
index 00000000000..9297959e759
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr38534-1.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move" }
*/
+
+#define ARRAY_SIZE 256
+
+extern int array[ARRAY_SIZE][ARRAY_SIZE][ARRAY_SIZE];
+extern int value (int, int, int)
+#ifndef __x86_64__
+__attribute__ ((regparm(3)))
+#endif
+;
+
+void
+__attribute__((noreturn))
+no_return_to_caller (void)
+{
+ unsigned i, j, k;
+ for (i = ARRAY_SIZE; i > 0; --i)
+ for (j = ARRAY_SIZE; j > 0; --j)
+ for (k = ARRAY_SIZE; k > 0; --k)
+ array[i - 1][j - 1][k - 1] = value (i, j, k);
+ while (1);
+}
+
+/* { dg-final { scan-assembler-not "push" } } */
+/* { dg-final { scan-assembler-not "pop" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr38534-2.c
b/gcc/testsuite/gcc.target/i386/pr38534-2.c
new file mode 100644
index 00000000000..1fb01363273
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr38534-2.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move" }
*/
+
+extern void bar (void) __attribute__ ((no_callee_saved_registers));
+extern void fn (void) __attribute__ ((noreturn));
+
+__attribute__ ((noreturn))
+void
+foo (void)
+{
+ bar ();
+ fn ();
+}
+
+/* { dg-final { scan-assembler-not "push" } } */
+/* { dg-final { scan-assembler-not "pop" } } */
+/* { dg-final { scan-assembler-not "jmp\[\\t \]+_?bar" } } */
+/* { dg-final { scan-assembler "call\[\\t \]+_?bar" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr38534-3.c
b/gcc/testsuite/gcc.target/i386/pr38534-3.c
new file mode 100644
index 00000000000..87fc35f3fe9
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr38534-3.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move" }
*/
+
+typedef void (*fn_t) (void) __attribute__ ((no_callee_saved_registers));
+extern fn_t bar;
+extern void fn (void) __attribute__ ((noreturn));
+
+__attribute__ ((noreturn))
+void
+foo (void)
+{
+ bar ();
+ fn ();
+}
+
+/* { dg-final { scan-assembler-not "push" } } */
+/* { dg-final { scan-assembler-not "pop" } } */
+/* { dg-final { scan-assembler-not "jmp" } } */
+/* { dg-final { scan-assembler "call\[\\t \]+" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr38534-4.c
b/gcc/testsuite/gcc.target/i386/pr38534-4.c
new file mode 100644
index 00000000000..561ebeef194
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr38534-4.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune-ctrl=^prologue_using_move,^epilogue_using_move" }
*/
+
+typedef void (*fn_t) (void) __attribute__ ((no_callee_saved_registers));
+extern void fn (void) __attribute__ ((noreturn));
+
+__attribute__ ((noreturn))
+void
+foo (fn_t bar)
+{
+ bar ();
+ fn ();
+}
+
+/* { dg-final { scan-assembler-not "push" } } */
+/* { dg-final { scan-assembler-not "pop" } } */
+/* { dg-final { scan-assembler-not "jmp" } } */
+/* { dg-final { scan-assembler "call\[\\t \]+" } } */
diff --git a/gcc/testsuite/gcc.target/i386/stack-check-17.c
b/gcc/testsuite/gcc.target/i386/stack-check-17.c
index b3e41cb3d25..061484e1319 100644
--- a/gcc/testsuite/gcc.target/i386/stack-check-17.c
+++ b/gcc/testsuite/gcc.target/i386/stack-check-17.c
@@ -23,19 +23,14 @@ f3 (void)
/* Verify no explicit probes. */
/* { dg-final { scan-assembler-not "or\[ql\]" } } */
-/* We also want to verify we did not use a push/pop sequence
- to probe *sp as the callee register saves are sufficient
- to probe *sp.
-
- y0/y1 are live across the call and thus must be allocated
+/* y0/y1 are live across the call and thus must be allocated
into either a stack slot or callee saved register. The former
would be rather dumb. So assume it does not happen.
- So search for two/four pushes for the callee register saves/argument pushes
- (plus one for the PIC register if needed on ia32) and no pops (since the
- function has no reachable epilogue). */
-/* { dg-final { scan-assembler-times "push\[ql\]" 2 { target { ! ia32 } } } }
*/
-/* { dg-final { scan-assembler-times "push\[ql\]" 4 { target { ia32 && nonpic
} } } } */
-/* { dg-final { scan-assembler-times "push\[ql\]" 5 { target { ia32 && { !
nonpic } } } } } */
-/* { dg-final { scan-assembler-not "pop" } } */
+ So search for a push/pop sequence for stack probe and 2 argument
+ pushes on ia32. There is no need to save and restore the PIC
+ register on ia32 for a noreturn function. */
+/* { dg-final { scan-assembler-times "push\[ql\]" 1 { target { ! ia32 } } } }
*/
+/* { dg-final { scan-assembler-times "push\[ql\]" 3 { target ia32 } } } */
+/* { dg-final { scan-assembler-times "pop" 1 } } */
--
2.43.0
