[gcc r14-4544] c++: mangle multiple levels of template parms [PR109422]

[Jason Merrill]

https://gcc.gnu.org/g:bd5719bd7f7cb23e5ed96a1f1a28efbb3dec4a31

commit r14-4544-gbd5719bd7f7cb23e5ed96a1f1a28efbb3dec4a31
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Oct 6 11:41:20 2023 -0400

    c++: mangle multiple levels of template parms [PR109422]
    
    This becomes be more important with concepts, but can also be seen with
    generic lambdas.
    
            PR c++/109422
    
    gcc/cp/ChangeLog:
    
            * mangle.cc (write_template_param): Also mangle level.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/lambda-generic-mangle1.C: New test.
            * g++.dg/cpp2a/lambda-generic-mangle1a.C: New test.

Diff:
---
 gcc/cp/mangle.cc                                     | 13 +++++++++++++
 gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1.C  |  9 +++++++++
 gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1a.C | 10 ++++++++++
 3 files changed, 32 insertions(+)

diff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc
index d88c779bfa2..d079f724910 100644
--- a/gcc/cp/mangle.cc
+++ b/gcc/cp/mangle.cc
@@ -3921,6 +3921,7 @@ static void
 write_template_param (const tree parm)
 {
   int parm_index;
+  int level;
 
   MANGLE_TRACE_TREE ("template-parm", parm);
 
@@ -3930,10 +3931,12 @@ write_template_param (const tree parm)
     case TEMPLATE_TEMPLATE_PARM:
     case BOUND_TEMPLATE_TEMPLATE_PARM:
       parm_index = TEMPLATE_TYPE_IDX (parm);
+      level = TEMPLATE_TYPE_LEVEL (parm);
       break;
 
     case TEMPLATE_PARM_INDEX:
       parm_index = TEMPLATE_PARM_IDX (parm);
+      level = TEMPLATE_PARM_LEVEL (parm);
       break;
 
     default:
@@ -3941,6 +3944,16 @@ write_template_param (const tree parm)
     }
 
   write_char ('T');
+  if (level > 1)
+    {
+      if (abi_warn_or_compat_version_crosses (19))
+	G.need_abi_warning = 1;
+      if (abi_version_at_least (19))
+	{
+	  write_char ('L');
+	  write_compact_number (level - 1);
+	}
+    }
   /* NUMBER as it appears in the mangling is (-1)-indexed, with the
      earliest template param denoted by `_'.  */
   write_compact_number (parm_index);
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1.C b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1.C
new file mode 100644
index 00000000000..0051307f53d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1.C
@@ -0,0 +1,9 @@
+// PR c++/109422
+// { dg-do compile { target c++20 } }
+
+struct C {
+  template<typename T>
+  void f(decltype([](T, auto) { return 0; })) {}
+};
+void g() { C().f<int>({}); }
+// { dg-final { scan-assembler "_ZN1C1fIiEEvDTtlNS_UlT_TL0__E_EEE" } }
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1a.C b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1a.C
new file mode 100644
index 00000000000..dc7b0125631
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-mangle1a.C
@@ -0,0 +1,10 @@
+// PR c++/109422
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fabi-version=18" }
+
+struct C {
+  template<typename T>
+  void f(decltype([](T, auto) { return 0; })) {}
+};
+void g() { C().f<int>({}); }
+// { dg-final { scan-assembler "_ZN1C1fIiEEvDTtlNS_UlT_T_E_EEE" } }