[PATCH] lto: Regenerate implicit section names after privatization [PR lto/126841]

IPA ICF can create address-preserving wrappers during WPA.  Expanding
such a wrapper resolves its implicit function-section name before LTO
privatizes the symbol.  The symbol is subsequently renamed with an
lto_priv suffix, but the section keeps the pre-privatization name.

Clear implicit section names on the renamed symbol and its aliases so
that LTRANS regenerates them from the final assembler name.  Leave
explicit user-specified section names unchanged.

Tested on x86_64-pc-linux-gnu.  The new test fails without the change and
passes with it.  The complete gcc.dg/lto and g++.dg/lto test suites have no
unexpected results.

	PR lto/126841

gcc/ChangeLog:

	* doc/invoke.texi (-ffunction-sections): Document implicitly generated
	section names under LTO.

gcc/lto/ChangeLog:

	* lto-partition.cc (clear_implicit_section): New.
	(privatize_symbol_name_1): Clear implicit section names after
	renaming.

gcc/testsuite/ChangeLog:

	* gcc.dg/lto/pr126841_0.c: New test.
	* gcc.dg/lto/pr126841_1.c: New test.
	* gcc.dg/lto/pr126841_2.c: New test.
	* gcc.dg/lto/pr126841_3.c: New test.

Signed-off-by: Longjun Luo <[email protected]>
---
The change is intentionally kept in privatize_symbol_name_1 rather than
symbol_table::change_decl_assembler_name.  LTO privatization is the path
covered by the reproducer and regression test; other assembler-name changes
have not been audited.

 gcc/doc/invoke.texi                   |  5 +++++
 gcc/lto/lto-partition.cc              | 12 ++++++++++++
 gcc/testsuite/gcc.dg/lto/pr126841_0.c | 22 ++++++++++++++++++++++
 gcc/testsuite/gcc.dg/lto/pr126841_1.c |  7 +++++++
 gcc/testsuite/gcc.dg/lto/pr126841_2.c |  7 +++++++
 gcc/testsuite/gcc.dg/lto/pr126841_3.c |  5 +++++
 6 files changed, 58 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/lto/pr126841_0.c
 create mode 100644 gcc/testsuite/gcc.dg/lto/pr126841_1.c
 create mode 100644 gcc/testsuite/gcc.dg/lto/pr126841_2.c
 create mode 100644 gcc/testsuite/gcc.dg/lto/pr126841_3.c

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 2e53a8c8a7e..e66cb895ae5 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -16927,6 +16927,11 @@ file if the target supports arbitrary sections.  The name of the
 function or the name of the data item determines the section's name
 in the output file.
 
+With link-time optimization, an implicitly generated section name is derived
+from the final assembler name, which may include a compiler-generated suffix
+to distinguish identically named internal-linkage items from different
+translation units.
+
 Use these options on systems where the linker can perform optimizations to
 improve locality of reference in the instruction space.  Most systems using the
 ELF object format have linkers with such optimizations.  On AIX, the linker
diff --git a/gcc/lto/lto-partition.cc b/gcc/lto/lto-partition.cc
index 5033ae3f97d..facb5d25907 100644
--- a/gcc/lto/lto-partition.cc
+++ b/gcc/lto/lto-partition.cc
@@ -1797,6 +1797,17 @@ validize_symbol_for_target (symtab_node *node)
 /* Maps symbol names to unique lto clone counters.  */
 static hash_map<const char *, unsigned> *lto_clone_numbers;
 
+/* Clear compiler-generated section names after changing an assembler name,
+   so they are regenerated from the final name.  */
+
+static bool
+clear_implicit_section (symtab_node *node, void *)
+{
+  if (node->implicit_section)
+    node->set_section_for_node (NULL);
+  return false;
+}
+
 /* Helper for privatize_symbol_name.  Mangle NODE symbol name
    represented by DECL.  */
 
@@ -1813,6 +1824,7 @@ privatize_symbol_name_1 (symtab_node *node, tree decl)
   symtab->change_decl_assembler_name (decl,
 				      clone_function_name (
 					  name, "lto_priv", clone_number));
+  node->call_for_symbol_and_aliases (clear_implicit_section, NULL, true);
   clone_number++;
 
   if (node->lto_file_data)
diff --git a/gcc/testsuite/gcc.dg/lto/pr126841_0.c b/gcc/testsuite/gcc.dg/lto/pr126841_0.c
new file mode 100644
index 00000000000..a0222d3336f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/lto/pr126841_0.c
@@ -0,0 +1,22 @@
+/* { dg-lto-do link } */
+/* { dg-require-effective-target elf } */
+/* { dg-require-effective-target named_sections } */
+/* { dg-require-effective-target fpic } */
+/* { dg-require-effective-target shared } */
+/* { dg-require-linker-plugin "" } */
+/* { dg-lto-options { { -O2 -flto -fPIC -shared -ffunction-sections -save-temps } } } */
+
+static int
+same_fn (int x)
+{
+  return x * 33 + 7;
+}
+
+int (*a_callback) (int) = same_fn;
+
+/* The exported function keeps the unsuffixed section, and each privatized
+   function must have its own section.  */
+/* { dg-final { scan-lto-assembler {\.section[ \t]+\.text\.same_fn[, \t"]} } } */
+/* { dg-final { scan-lto-assembler {\.section[ \t]+\.text\.same_fn\.lto_priv\.0[, \t"]} } } */
+/* { dg-final { scan-lto-assembler {\.section[ \t]+\.text\.same_fn\.lto_priv\.1[, \t"]} } } */
+/* { dg-final { scan-lto-assembler {\.section[ \t]+\.text\.same_fn\.lto_priv\.2[, \t"]} } } */
diff --git a/gcc/testsuite/gcc.dg/lto/pr126841_1.c b/gcc/testsuite/gcc.dg/lto/pr126841_1.c
new file mode 100644
index 00000000000..39356acba71
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/lto/pr126841_1.c
@@ -0,0 +1,7 @@
+static int
+same_fn (int x)
+{
+  return x * 33 + 7;
+}
+
+int (*b_callback) (int) = same_fn;
diff --git a/gcc/testsuite/gcc.dg/lto/pr126841_2.c b/gcc/testsuite/gcc.dg/lto/pr126841_2.c
new file mode 100644
index 00000000000..369eb1836a6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/lto/pr126841_2.c
@@ -0,0 +1,7 @@
+static int
+same_fn (int x)
+{
+  return x * 33 + 7;
+}
+
+int (*c_callback) (int) = same_fn;
diff --git a/gcc/testsuite/gcc.dg/lto/pr126841_3.c b/gcc/testsuite/gcc.dg/lto/pr126841_3.c
new file mode 100644
index 00000000000..567eb29cda0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/lto/pr126841_3.c
@@ -0,0 +1,5 @@
+int
+same_fn (int x)
+{
+  return x - 1;
+}
-- 
2.55.0