[clang] [clang] Fix for Assertion `(T->hasSignedIntegerRepresentation() || T->isSignedFixedPointType()) && "Unexpected signed integer or fixed point type"' failed. (PR #195945)

[via cfe-commits]

https://github.com/PrabbyDD updated https://github.com/llvm/llvm-project/pull/195945

>From 36ce4b83c0c674cdc6439f49a90c59ee5bdc613a Mon Sep 17 00:00:00 2001
From: PrabbyDD <dhaliprabh at gmail.com>
Date: Tue, 5 May 2026 14:16:55 -0700
Subject: [PATCH 1/2] Fix crash by checking for the type signage before
 entering getCorrespondingSignedType()

---
 clang/docs/ReleaseNotes.rst                |  1 +
 clang/lib/Sema/SemaExpr.cpp                | 18 +++++++++++-------
 clang/test/Sema/va_arg_enum_underlying.cpp | 15 +++++++++++++++
 3 files changed, 27 insertions(+), 7 deletions(-)
 create mode 100644 clang/test/Sema/va_arg_enum_underlying.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ec64c2008d89b..f01a73739d8e0 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -519,6 +519,7 @@ Bug Fixes in This Version
 - Clang now emits an error for friend declarations of lambda members. (#GH26540)
 - Fixed a crash caused by lambda capture handling in delayed default arguments. (#GH176534)
 - Fixed a crash when parsing invalid ``static_assert`` declarations with string-literal messages (#GH187690).
+- Fixed an assert/crash in ``__builtin_va_arg`` when the argument type is an enum without a correspoding signed type (#GH191698).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index c494669420282..2712acb0d0936 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -17314,13 +17314,17 @@ ExprResult Sema::BuildVAArgExpr(SourceLocation BuiltinLoc,
       if (!PromoteType.isNull() && !UnderlyingType->isBooleanType() &&
           PromoteType->isUnsignedIntegerType() !=
               UnderlyingType->isUnsignedIntegerType()) {
-        UnderlyingType =
-            UnderlyingType->isUnsignedIntegerType()
-                ? Context.getCorrespondingSignedType(UnderlyingType)
-                : Context.getCorrespondingUnsignedType(UnderlyingType);
-        if (Context.typesAreCompatible(PromoteType, UnderlyingType,
-                                       /*CompareUnqualified*/ true))
-          PromoteType = QualType();
+
+        if (!UnderlyingType->isUnsignedIntegerType() ||
+            UnderlyingType->hasSignedIntegerRepresentation()) {
+          UnderlyingType =
+              UnderlyingType->isUnsignedIntegerType()
+                  ? Context.getCorrespondingSignedType(UnderlyingType)
+                  : Context.getCorrespondingUnsignedType(UnderlyingType);
+          if (Context.typesAreCompatible(PromoteType, UnderlyingType,
+                                         /*CompareUnqualified*/ true))
+            PromoteType = QualType();
+        }
       }
     }
     if (TInfo->getType()->isSpecificBuiltinType(BuiltinType::Float))
diff --git a/clang/test/Sema/va_arg_enum_underlying.cpp b/clang/test/Sema/va_arg_enum_underlying.cpp
new file mode 100644
index 0000000000000..e4962f4e1326e
--- /dev/null
+++ b/clang/test/Sema/va_arg_enum_underlying.cpp
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
+
+__builtin_va_list ap;
+
+void foo() {
+  enum E1 : char16_t {};
+  enum E2 : char32_t {};
+  enum E3 : unsigned char {};
+  enum E4 : wchar_t {};
+
+  (void)__builtin_va_arg(ap, E1); // expected-warning {{second argument to 'va_arg' is of promotable type}}
+  (void)__builtin_va_arg(ap, E2); // expected-warning {{second argument to 'va_arg' is of promotable type}}
+  (void)__builtin_va_arg(ap, E3); // expected-warning {{second argument to 'va_arg' is of promotable type}}
+  (void)__builtin_va_arg(ap, E4); // expected-warning {{second argument to 'va_arg' is of promotable type}}
+}

>From 14b664ec4a3b1251679b71c93f3eca3e37168d8f Mon Sep 17 00:00:00 2001
From: PrabbyDD <dhaliprabh at gmail.com>
Date: Tue, 5 May 2026 14:46:42 -0700
Subject: [PATCH 2/2] adding an expected warning to varargs test since we now
 emit that

---
 clang/test/SemaCXX/varargs.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/test/SemaCXX/varargs.cpp b/clang/test/SemaCXX/varargs.cpp
index 1e5920a8728d3..c84d765296e88 100644
--- a/clang/test/SemaCXX/varargs.cpp
+++ b/clang/test/SemaCXX/varargs.cpp
@@ -31,7 +31,7 @@ void record_context(int a, ...) {
 // Ensure the correct behavior for promotable type UB checking.
 void promotable(int a, ...) {
   enum Unscoped1 { One = 0x7FFFFFFF };
-  (void)__builtin_va_arg(ap, Unscoped1); // ok
+  (void)__builtin_va_arg(ap, Unscoped1); // expected-warning {{second argument to 'va_arg' is of promotable type}}
 
   enum Unscoped2 { Two = 0xFFFFFFFF };
   (void)__builtin_va_arg(ap, Unscoped2); // ok