[clang] [clang] Fix crashes when passing VLA to va_arg (PR #119563)

[via cfe-commits]

https://github.com/amane-ame updated https://github.com/llvm/llvm-project/pull/119563

>From 659eda3ec76b63418f8b621b004728d9d7bf26ad Mon Sep 17 00:00:00 2001
From: amane-ame <i at amane-a.me>
Date: Wed, 11 Dec 2024 22:17:51 +0800
Subject: [PATCH 1/3] [clang] Fix crashes when passing VLA to va_arg

---
 clang/lib/CodeGen/CGExprAgg.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 2ad6587089f101..a4111cb65c8b1c 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -2201,6 +2201,8 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
     // But note that getTypeInfo returns 0 for a VLA.
     if (auto *VAT = dyn_cast_or_null<VariableArrayType>(
             getContext().getAsArrayType(Ty))) {
+      assert(Ty->isVariableArrayType());
+      EmitVariablyModifiedType(Ty);
       QualType BaseEltTy;
       SizeVal = emitArrayLength(VAT, BaseEltTy, DestPtr);
       TypeInfo = getContext().getTypeInfoInChars(BaseEltTy);

>From 5937db790ff0a59ea5bf18cb008d38a4524dc7dc Mon Sep 17 00:00:00 2001
From: amane-ame <i at amane-a.me>
Date: Thu, 12 Dec 2024 13:50:13 +0800
Subject: [PATCH 2/3] [clang] Add a testcase for passing VLA to va_arg

---
 clang/test/CodeGen/varargs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/clang/test/CodeGen/varargs.c b/clang/test/CodeGen/varargs.c
index 625399b87f7ad7..b7b1b52156be37 100644
--- a/clang/test/CodeGen/varargs.c
+++ b/clang/test/CodeGen/varargs.c
@@ -20,4 +20,7 @@ void vla(int n, ...)
   __builtin_va_list ap;
   void *p;
   p = __builtin_va_arg(ap, typeof (int (*)[++n])); // CHECK: add nsw i32 {{.*}}, 1
+  // Don't crash on some undefined behaviors.
+  p = __builtin_va_arg(ap, typeof (int [++n]));
+  p = __builtin_va_arg(ap, typeof (int [n][n]));
 }

>From df9f8f61ee21b81c9cfd300d113afea9298b8067 Mon Sep 17 00:00:00 2001
From: amane-ame <i at amane-a.me>
Date: Thu, 12 Dec 2024 13:52:59 +0800
Subject: [PATCH 3/3] [clang] Move the parsing of VLA in va_arg to EmitVAArg

---
 clang/lib/CodeGen/CGCall.cpp    | 2 ++
 clang/lib/CodeGen/CGExprAgg.cpp | 2 --
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 3cefc9da66ddb8..4e2812c62f4357 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -6121,6 +6121,8 @@ RValue CodeGenFunction::EmitVAArg(VAArgExpr *VE, Address &VAListAddr,
   VAListAddr = VE->isMicrosoftABI() ? EmitMSVAListRef(VE->getSubExpr())
                                     : EmitVAListRef(VE->getSubExpr());
   QualType Ty = VE->getType();
+  if (Ty->isVariableArrayType())
+    EmitVariablyModifiedType(Ty);
   if (VE->isMicrosoftABI())
     return CGM.getABIInfo().EmitMSVAArg(*this, VAListAddr, Ty, Slot);
   return CGM.getABIInfo().EmitVAArg(*this, VAListAddr, Ty, Slot);
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index a4111cb65c8b1c..2ad6587089f101 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -2201,8 +2201,6 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
     // But note that getTypeInfo returns 0 for a VLA.
     if (auto *VAT = dyn_cast_or_null<VariableArrayType>(
             getContext().getAsArrayType(Ty))) {
-      assert(Ty->isVariableArrayType());
-      EmitVariablyModifiedType(Ty);
       QualType BaseEltTy;
       SizeVal = emitArrayLength(VAT, BaseEltTy, DestPtr);
       TypeInfo = getContext().getTypeInfoInChars(BaseEltTy);