[clang] [clang] Fix crash related to _BitInt constant split (PR #112218)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: Mariya Podchishchaeva (Fznamznon)

<details>
<summary>Changes</summary>

9ad72df55cb74b29193270c28f6974d2af8e0b71 added split of _BitInt constants when required. Before folding back, check that the constant exists.

---
Full diff: https://github.com/llvm/llvm-project/pull/112218.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGDecl.cpp (+1-1) 
- (modified) clang/test/CodeGenCXX/ext-int.cpp (+15) 


``````````diff
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 30af9268b30e2e..1d0660292cecc1 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1945,7 +1945,7 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
                                   replaceUndef(CGM, isPattern, constant));
     }
 
-    if (D.getType()->isBitIntType() &&
+    if (constant && D.getType()->isBitIntType() &&
         CGM.getTypes().typeRequiresSplitIntoByteArray(D.getType())) {
       // Constants for long _BitInt types are split into individual bytes.
       // Try to fold these back into an integer constant so it can be stored
diff --git a/clang/test/CodeGenCXX/ext-int.cpp b/clang/test/CodeGenCXX/ext-int.cpp
index 7758e92d74a05f..a098f5a9057c0e 100644
--- a/clang/test/CodeGenCXX/ext-int.cpp
+++ b/clang/test/CodeGenCXX/ext-int.cpp
@@ -614,3 +614,18 @@ void TBAATest(_BitInt(sizeof(int) * 8) ExtInt,
 // NewStructPathTBAA-DAG: ![[EXTINT_TBAA_ROOT]] = !{![[CHAR_TBAA_ROOT]], i64 4, !"_BitInt(32)"}
 // NewStructPathTBAA-DAG: ![[EXTINT6_TBAA]] = !{![[EXTINT6_TBAA_ROOT:.+]], ![[EXTINT6_TBAA_ROOT]], i64 0, i64 1}
 // NewStructPathTBAA-DAG: ![[EXTINT6_TBAA_ROOT]] = !{![[CHAR_TBAA_ROOT]], i64 1, !"_BitInt(6)"}
+
+namespace A {
+template <int N> struct S {
+  using T = _BitInt(N);
+  T Data;
+};
+template <int N> void foo(S<N> B) {
+  const auto Var = B.Data;
+}
+
+void bar() {
+  S<2080> a;
+  foo(a);
+}
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/112218