x86-64: Use R11 for DRAP register in preserve_none functions

In 64-bit mode, for preserve_none functions, DRAP may use any register
except AX, R12–R15, DI, SI (argument registers), SP, and BP. Use R11.
In non-callee-saved functions, R10 and R13 are also available since they
are not used for parameter passing.  In 32-bit mode, preserve_none does
not affect parameter passing, so the current approach remains valid.

DRAP register is used to restore stack pointer in epilogue for stack
realignment.  Always save and restore DRAP register between prologue
and epilogue so that stack pointer can be restored.

Tested with CPython 3.14.4 on Linux/x86-64.

gcc/

	PR target/120870
	* config/i386/i386.cc (ix86_save_reg): Return true for DRAP
	register early at entry.
	(find_drap_reg): Use R11_REG in preserve_none functions in
	64-bit mode.

gcc/testsuite/

	PR target/120870
	* gcc.target/i386/pr120870-1.c: New test.
	* gcc.target/i386/pr120870-2.c: Likewise.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Co-Authored-By: Uros Bizjak <ubizjak@gmail.com>

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 9aecd51119f3f85525910f29c0ca02ebf1cb9f7f..2744c74957802c27e577e06ec7dbc3df84a151df 100644 (file)
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -6776,6 +6776,13 @@ ix86_save_reg (unsigned int regno, bool maybe_eh_return, bool ignore_outlined)
 {
   rtx reg;
 
+  /* Save and restore DRAP register between prologue and epilogue so
+     that stack pointer can be restored.  */
+  if (crtl->drap_reg
+      && regno == REGNO (crtl->drap_reg)
+      && !cfun->machine->no_drap_save_restore)
+    return true;
+
   switch (cfun->machine->call_saved_registers)
     {
     case TYPE_DEFAULT_CALL_SAVED_REGISTERS:
@@ -6851,11 +6858,6 @@ ix86_save_reg (unsigned int regno, bool maybe_eh_return, bool ignore_outlined)
        return false;
     }
 
-  if (crtl->drap_reg
-      && regno == REGNO (crtl->drap_reg)
-      && !cfun->machine->no_drap_save_restore)
-    return true;
-
   return (df_regs_ever_live_p (regno)
          && !call_used_or_fixed_reg_p (regno)
          && (regno != HARD_FRAME_POINTER_REGNUM || !frame_pointer_needed));
@@ -7946,6 +7948,11 @@ find_drap_reg (void)
      registers.  */
   if (TARGET_64BIT)
     {
+      /* In preserve_none functions, any register can be used for DRAP,
+        except AX, R12–R15, DI, SI (argument registers), SP, and BP.  */
+      if (cfun->machine->call_saved_registers == TYPE_PRESERVE_NONE)
+       return R11_REG;
+
       /* Use R13 for nested function or function need static chain.
         Since function with tail call may use any caller-saved
         registers in epilogue, DRAP must not use caller-saved

diff --git a/gcc/testsuite/gcc.target/i386/pr120870-1.c b/gcc/testsuite/gcc.target/i386/pr120870-1.c
new file mode 100644 (file)
index 0000000..21e38d2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr120870-1.c
@@ -0,0 +1,35 @@
+/* { dg-do run } */
+/* { dg-options "-O0 -march=x86-64-v3" } */
+
+void
+ext (long a, long b, long c, long d, long e, long f, long g)
+{
+}
+
+void
+tail (long a, long b)
+{
+}
+
+__attribute__ ((preserve_none)) void
+caller (long a, long b, long c, long d, long e, long f, long g)
+{
+  __attribute__ ((aligned (32))) long x[4]; // for stack alignment
+  ext (a, b, c, d, e, f, g);
+  __attribute__ ((musttail)) return tail (a + b, b + c);
+}
+
+__attribute__ ((noipa))
+static void
+do_test ()
+{
+  caller (1, 2, 3, 4, 5, 6, 7);
+}
+
+int
+main (void)
+{
+  if (__builtin_cpu_supports ("x86-64-v3"))
+    do_test ();
+  return 0;
+}

diff --git a/gcc/testsuite/gcc.target/i386/pr120870-2.c b/gcc/testsuite/gcc.target/i386/pr120870-2.c
new file mode 100644 (file)
index 0000000..7e68718
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr120870-2.c
@@ -0,0 +1,6 @@
+/* { dg-do run } */
+/* { dg-options "-O0 -march=x86-64-v3" } */
+
+#define preserve_none no_callee_saved_registers
+
+#include "pr120870-1.c"