commit 75179275ecc35724a058676199188e0d13e65054
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Fri Nov 3 20:30:53 2017 +0000

            * config/i386/i386.c (ix86_emit_restore_reg_using_pop): Prototype.
            (ix86_adjust_stack_and_probe_stack_clash): Use a push/pop sequence
            to probe at the start of a noreturn function.
    
            * gcc.target/i386/stack-check-12.c: New test.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@254396 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index fd74f1f6c0c..3c828ba492d 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -96,6 +96,7 @@ static rtx legitimize_dllimport_symbol (rtx, bool);
 static rtx legitimize_pe_coff_extern_decl (rtx, bool);
 static rtx legitimize_pe_coff_symbol (rtx, bool);
 static void ix86_print_operand_address_as (FILE *, rtx, addr_space_t, bool);
+static void ix86_emit_restore_reg_using_pop (rtx);
 
 #ifndef CHECK_STACK_LIMIT
 #define CHECK_STACK_LIMIT (-1)
@@ -13287,10 +13288,13 @@ ix86_adjust_stack_and_probe_stack_clash (const HOST_WIDE_INT size)
      no probes are needed.  */
   if (!size)
     {
+      struct ix86_frame frame;
+      ix86_compute_frame_layout (&frame);
+
       /* However, the allocation of space via pushes for register
 	 saves could be viewed as allocating space, but without the
 	 need to probe.  */
-      if (m->frame.nregs || m->frame.nsseregs || frame_pointer_needed)
+      if (frame.nregs || frame.nsseregs || frame_pointer_needed)
         dump_stack_clash_frame_info (NO_PROBE_SMALL_FRAME, true);
       else
 	dump_stack_clash_frame_info (NO_PROBE_NO_FRAME, false);
@@ -13312,8 +13316,14 @@ ix86_adjust_stack_and_probe_stack_clash (const HOST_WIDE_INT size)
      we just probe when we cross PROBE_INTERVAL.  */
   if (TREE_THIS_VOLATILE (cfun->decl))
     {
-      emit_stack_probe (plus_constant (Pmode, stack_pointer_rtx,
-				       -GET_MODE_SIZE (word_mode)));
+      /* We can safely use any register here since we're just going to push
+	 its value and immediately pop it back.  But we do try and avoid
+	 argument passing registers so as not to introduce dependencies in
+	 the pipeline.  For 32 bit we use %esi and for 64 bit we use %rax.  */
+      rtx dummy_reg = gen_rtx_REG (word_mode, TARGET_64BIT ? AX_REG : SI_REG);
+      rtx_insn *insn = emit_insn (gen_push (dummy_reg));
+      RTX_FRAME_RELATED_P (insn) = 1;
+      ix86_emit_restore_reg_using_pop (dummy_reg);
       emit_insn (gen_blockage ());
     }
 
diff --git a/gcc/testsuite/gcc.target/i386/stack-check-12.c b/gcc/testsuite/gcc.target/i386/stack-check-12.c
new file mode 100644
index 00000000000..cb69bb08086
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/stack-check-12.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection -mtune=generic" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+__attribute__ ((noreturn)) void exit (int);
+
+__attribute__ ((noreturn)) void
+f (void)
+{
+  asm volatile ("nop" ::: "edi");
+  exit (1);
+}
+
+/* { dg-final { scan-assembler-not "or\[ql\]" } } */
+/* { dg-final { scan-assembler "pushl	%esi" { target ia32 } } } */
+/* { dg-final { scan-assembler "popl	%esi" { target ia32 } } }*/
+/* { dg-final { scan-assembler "pushq	%rax" { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler "popq	%rax" { target { ! ia32 } } } }*/
+