[clang] [X86] Fix CodeGen crash for arrays of empty structs and unions (PR #224203)

[via cfe-commits]

llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: MaoJian (MaooJian)

<details>
<summary>Changes</summary>

getFPTypeAtOffset() divides by the allocation size of an array element when normalizing IROffset. Empty structs and unions have zero allocation size, so arrays of these types can cause a division-by-zero during X86 ABI lowering.

Return nullptr for zero-sized array elements and add CodeGen tests for empty struct and union arrays.

---
Full diff: https://github.com/llvm/llvm-project/pull/224203.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/Targets/X86.cpp (+2) 
- (added) clang/test/CodeGen/X86/empty-struct-union-array.c (+29) 


``````````diff
diff --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp
index 14fe5ffae8372..21f9929cfa882 100644
--- a/clang/lib/CodeGen/Targets/X86.cpp
+++ b/clang/lib/CodeGen/Targets/X86.cpp
@@ -2528,6 +2528,8 @@ static llvm::Type *getFPTypeAtOffset(llvm::Type *IRType, unsigned IROffset,
   if (llvm::ArrayType *ATy = dyn_cast<llvm::ArrayType>(IRType)) {
     llvm::Type *EltTy = ATy->getElementType();
     unsigned EltSize = TD.getTypeAllocSize(EltTy);
+    if (EltSize == 0)
+      return nullptr;
     IROffset -= IROffset / EltSize * EltSize;
     return getFPTypeAtOffset(EltTy, IROffset, TD);
   }
diff --git a/clang/test/CodeGen/X86/empty-struct-union-array.c b/clang/test/CodeGen/X86/empty-struct-union-array.c
new file mode 100644
index 0000000000000..37efe8dbfde4b
--- /dev/null
+++ b/clang/test/CodeGen/X86/empty-struct-union-array.c
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -triple=x86_64 -emit-llvm -o - %s | FileCheck %s
+
+struct StructArray {
+    long a;
+    float b;
+    struct {
+    } c[7];
+}
+
+struct UnionArray {
+    long a;
+    float b;
+    union {
+    } c[7];
+}
+
+// CHECK-LABEL: define{{.*}} @foo_struct
+// CHECK: ret
+struct StructArray foo_struct() {
+    struct StructArray s;
+    return s;
+}
+
+// CHECK-LABEL: define{{.*}} @foo_union
+// CHECK: ret
+struct UnionArray foo_union() {
+    struct UnionArray s;
+    return s;
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/224203