From 20f56d140909a01c74e9981835373eaab6021af9 Mon Sep 17 00:00:00 2001
From: Larry Meadows <lmeadows@amd.com>
Date: Wed, 25 Jun 2025 12:06:11 -0700
Subject: [PATCH] [libc++abi] Fix C++ demangling for _BitInt type (#143466)

The front-end expects _BitInt to be available for substitution; ensure DB<n> is
added to Subs in ItaniumDemangle.h. Also add a test case to libc++abi and
sync the files to llvm/include/llvm.
---
 libcxxabi/src/demangle/ItaniumDemangle.h                 | 4 +++-
 libcxxabi/test/DemangleTestCases.inc                     | 1 +
 llvm/include/llvm/Demangle/ItaniumDemangle.h             | 4 +++-
 llvm/include/llvm/Testing/Demangle/DemangleTestCases.inc | 1 +
 4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h
index 4e7f92dd1991..b306b2013445 100644
--- a/libcxxabi/src/demangle/ItaniumDemangle.h
+++ b/libcxxabi/src/demangle/ItaniumDemangle.h
@@ -4468,7 +4468,9 @@ Node *AbstractManglingParser<Derived, Alloc>::parseType() {
         return nullptr;
       if (!consumeIf('_'))
         return nullptr;
-      return make<BitIntType>(Size, Signed);
+      // The front end expects this to be available for Substitution
+      Result = make<BitIntType>(Size, Signed);
+      break;
     }
     //                ::= Di   # char32_t
     case 'i':
diff --git a/libcxxabi/test/DemangleTestCases.inc b/libcxxabi/test/DemangleTestCases.inc
index 1e3f7459deaa..2721d2aa5504 100644
--- a/libcxxabi/test/DemangleTestCases.inc
+++ b/libcxxabi/test/DemangleTestCases.inc
@@ -6,6 +6,7 @@
 {"_Z1fDU10_", "f(unsigned _BitInt(10))"},
 {"_Z1fIfEvDUstPT__", "void f<float>(unsigned _BitInt(sizeof (float*)))"},
 {"_Z1fIiEvDBstPT__", "void f<int>(_BitInt(sizeof (int*)))"},
+{"_Z6myfuncRDB8_S0_", "myfunc(_BitInt(8)&, _BitInt(8)&)"},
 {"_Z4testI1A1BE1Cv", "C test<A, B>()"},
 {"_Z4testI1A1BET0_T_S3_", "B test<A, B>(A, A)"},
 {"_ZN1SgtEi", "S::operator>(int)"},
diff --git a/llvm/include/llvm/Demangle/ItaniumDemangle.h b/llvm/include/llvm/Demangle/ItaniumDemangle.h
index f4569850b093..5533652736dc 100644
--- a/llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ b/llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -4468,7 +4468,9 @@ Node *AbstractManglingParser<Derived, Alloc>::parseType() {
         return nullptr;
       if (!consumeIf('_'))
         return nullptr;
-      return make<BitIntType>(Size, Signed);
+      // The front end expects this to be available for Substitution
+      Result = make<BitIntType>(Size, Signed);
+      break;
     }
     //                ::= Di   # char32_t
     case 'i':
diff --git a/llvm/include/llvm/Testing/Demangle/DemangleTestCases.inc b/llvm/include/llvm/Testing/Demangle/DemangleTestCases.inc
index 1e3f7459deaa..2721d2aa5504 100644
--- a/llvm/include/llvm/Testing/Demangle/DemangleTestCases.inc
+++ b/llvm/include/llvm/Testing/Demangle/DemangleTestCases.inc
@@ -6,6 +6,7 @@
 {"_Z1fDU10_", "f(unsigned _BitInt(10))"},
 {"_Z1fIfEvDUstPT__", "void f<float>(unsigned _BitInt(sizeof (float*)))"},
 {"_Z1fIiEvDBstPT__", "void f<int>(_BitInt(sizeof (int*)))"},
+{"_Z6myfuncRDB8_S0_", "myfunc(_BitInt(8)&, _BitInt(8)&)"},
 {"_Z4testI1A1BE1Cv", "C test<A, B>()"},
 {"_Z4testI1A1BET0_T_S3_", "B test<A, B>(A, A)"},
 {"_ZN1SgtEi", "S::operator>(int)"},