[PATCH v3] x86: Save callee-saved registers in noreturn functions for -O0/-Og

[H.J. Lu]

Changes in v3:

1. Add the TREE_THIS_VOLATILE check to minimize noreturn attribute lookup.

Changes in v2:

1. Lookup noreturn attribute first.
2. Use __attribute__((noreturn, optimize("-Og"))) in pr38534-6.c.

----
Save callee-saved registers in noreturn functions for -O0/-Og so that
debugger can restore callee-saved registers in caller's frame.

Also add the TREE_THIS_VOLATILE check to minimize noreturn attribute
lookup.

gcc/

        PR target/38534
        * config/i386/i386-options.cc (ix86_set_func_type): Save
        callee-saved registers in noreturn functions for -O0/-Og.

gcc/testsuite/

        PR target/38534
        * gcc.target/i386/pr38534-5.c: New file.
        * gcc.target/i386/pr38534-6.c: Likewise.
---
 gcc/config/i386/i386-options.cc           | 12 +++++++----
 gcc/testsuite/gcc.target/i386/pr38534-5.c | 26 +++++++++++++++++++++++
 gcc/testsuite/gcc.target/i386/pr38534-6.c | 26 +++++++++++++++++++++++
 3 files changed, 60 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-5.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-6.c

diff --git a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc
index 473f5359fc9..8f5ce817630 100644
--- a/gcc/config/i386/i386-options.cc
+++ b/gcc/config/i386/i386-options.cc
@@ -3381,9 +3381,10 @@ 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.
+     function with nothrow or compiled with -fno-exceptions unless when
+     compiling with -O0 or -Og.
 
-     NB: Don't use TREE_THIS_VOLATILE to check if this is a noreturn
+     NB: Can't use just 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.
@@ -3391,8 +3392,11 @@ ix86_set_func_type (tree fndecl)
      function is marked as noreturn in the IR output, which leads the
      incompatible attribute error in LTO1.  */
   bool has_no_callee_saved_registers
-    = (((TREE_NOTHROW (fndecl) || !flag_exceptions)
-       && lookup_attribute ("noreturn", DECL_ATTRIBUTES (fndecl)))
+    = ((TREE_THIS_VOLATILE (fndecl)
+       && lookup_attribute ("noreturn", DECL_ATTRIBUTES (fndecl))
+       && optimize
+       && !optimize_debug
+       && (TREE_NOTHROW (fndecl) || !flag_exceptions))
        || lookup_attribute ("no_callee_saved_registers",
                            TYPE_ATTRIBUTES (TREE_TYPE (fndecl))));
 
diff --git a/gcc/testsuite/gcc.target/i386/pr38534-5.c 
b/gcc/testsuite/gcc.target/i386/pr38534-5.c
new file mode 100644
index 00000000000..91c0c0f8c59
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr38534-5.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O0 -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 "push" } } */
+/* { dg-final { scan-assembler-not "pop" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr38534-6.c 
b/gcc/testsuite/gcc.target/i386/pr38534-6.c
new file mode 100644
index 00000000000..cf1463a9c66
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr38534-6.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, optimize("-Og")))
+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 "push" } } */
+/* { dg-final { scan-assembler-not "pop" } } */
-- 
2.43.0