I've discovered a problem with -mlong-calls on ARM. The bug was first
reported against a new target, but I'd copied the relevant code from the
ARM backend.
We use current_function_section in arm_is_long_call_p to decide whether
we're calling something that goes into the same section. The problem
with this is that current_function_section can only be used during
final, since it relies on the global variable in_cold_section_p which is
set up only in assemble_start_function. On ARM, this problem manifests
as short-calls when a long-call would be required; in the other port it
was an "insn doesn't satisfy its constraints" error.
The following patch is against 4.5, since the problem appears hidden in
mainline (the initialization of first_function_block_is_cold has
changed). Ok for trunk and branches after arm-linux tests complete?
Bernd
* function.c (init_function_start): Call decide_function_section.
* varasm.c (decide_function_section): New function.
(assemble_start_function): When not using
flag_reorder_blocks_and_partition, don't compute in_cold_section_p
or first_function_block_is_cold.
* rtl.h (decide_function_section): Declare.
* gcc.target/arm/cold-lc.c: New test.
Index: gcc/testsuite/gcc.target/arm/cold-lc.c
===================================================================
--- gcc/testsuite/gcc.target/arm/cold-lc.c (revision 0)
+++ gcc/testsuite/gcc.target/arm/cold-lc.c (revision 0)
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mlong-calls" } */
+/* { dg-final { scan-assembler-not "bl\[^\n\]*dump_stack" } } */
+
+extern void dump_stack (void) __attribute__ ((__cold__)) __attribute__
((noinline));
+struct thread_info {
+ struct task_struct *task;
+};
+extern struct thread_info *current_thread_info (void);
+
+void dump_stack (void)
+{
+ unsigned long stack;
+ show_stack ((current_thread_info ()->task), &stack);
+}
+
+void die (char *str, void *fp, int nr)
+{
+ dump_stack ();
+ while (1);
+}
+
Index: gcc/function.c
===================================================================
--- gcc/function.c (revision 170052)
+++ gcc/function.c (working copy)
@@ -4227,6 +4227,7 @@ init_function_start (tree subr)
else
allocate_struct_function (subr, false);
prepare_function_start ();
+ decide_function_section (subr);
/* Warn if this value is an aggregate type,
regardless of which calling convention we are using for it. */
Index: gcc/varasm.c
===================================================================
--- gcc/varasm.c (revision 170052)
+++ gcc/varasm.c (working copy)
@@ -1687,6 +1687,38 @@ notice_global_symbol (tree decl)
}
}
+/* If not using flag_reorder_blocks_and_partition, decide early whether the
+ current function goes into the cold section, so that targets can use
+ current_function_section during RTL expansion. DECL describes the
+ function. */
+
+void
+decide_function_section (tree decl)
+{
+ first_function_block_is_cold = false;
+
+ if (flag_reorder_blocks_and_partition)
+ /* We will decide in assemble_start_function. */
+ return;
+
+ if (DECL_SECTION_NAME (decl))
+ {
+ /* Calls to function_section rely on first_function_block_is_cold
+ being accurate. The first block may be cold even if we aren't
+ doing partitioning, if the entire function was decided by
+ choose_function_section (predict.c) to be cold. */
+
+ initialize_cold_section_name ();
+
+ if (crtl->subsections.unlikely_text_section_name
+ && strcmp (TREE_STRING_POINTER (DECL_SECTION_NAME (decl)),
+ crtl->subsections.unlikely_text_section_name) == 0)
+ first_function_block_is_cold = true;
+ }
+
+ in_cold_section_p = first_function_block_is_cold;
+}
+
/* Output assembler code for the constant pool of a function and associated
with defining the name of the function. DECL describes the function.
NAME is the function's name. For the constant pool, we use the current
@@ -1701,7 +1733,6 @@ assemble_start_function (tree decl, cons
crtl->subsections.unlikely_text_section_name = NULL;
- first_function_block_is_cold = false;
if (flag_reorder_blocks_and_partition)
{
ASM_GENERATE_INTERNAL_LABEL (tmp_label, "LHOTB", const_labelno);
@@ -1738,6 +1769,8 @@ assemble_start_function (tree decl, cons
if (flag_reorder_blocks_and_partition)
{
+ first_function_block_is_cold = false;
+
switch_to_section (unlikely_text_section ());
assemble_align (DECL_ALIGN (decl));
ASM_OUTPUT_LABEL (asm_out_file, crtl->subsections.cold_section_label);
@@ -1754,23 +1787,8 @@ assemble_start_function (tree decl, cons
hot_label_written = true;
first_function_block_is_cold = true;
}
+ in_cold_section_p = first_function_block_is_cold;
}
- else if (DECL_SECTION_NAME (decl))
- {
- /* Calls to function_section rely on first_function_block_is_cold
- being accurate. The first block may be cold even if we aren't
- doing partitioning, if the entire function was decided by
- choose_function_section (predict.c) to be cold. */
-
- initialize_cold_section_name ();
-
- if (crtl->subsections.unlikely_text_section_name
- && strcmp (TREE_STRING_POINTER (DECL_SECTION_NAME (decl)),
- crtl->subsections.unlikely_text_section_name) == 0)
- first_function_block_is_cold = true;
- }
-
- in_cold_section_p = first_function_block_is_cold;
/* Switch to the correct text section for the start of the function. */
Index: gcc/rtl.h
===================================================================
--- gcc/rtl.h (revision 170052)
+++ gcc/rtl.h (working copy)
@@ -1644,6 +1644,7 @@ extern rtx get_pool_constant (rtx);
extern rtx get_pool_constant_mark (rtx, bool *);
extern enum machine_mode get_pool_mode (const_rtx);
extern rtx simplify_subtraction (rtx);
+extern void decide_function_section (tree);
/* In function.c */
extern rtx assign_stack_local (enum machine_mode, HOST_WIDE_INT, int);
