[clang] [llvm] [SROA] Fix assertion failure when promoting self-referential load/store (PR #208826)

[Krisitan Erik Olsen via cfe-commits]

https://github.com/Kristianerik updated https://github.com/llvm/llvm-project/pull/208826

>From e35009d0fa95e12c81b045e42480c19142838f7f Mon Sep 17 00:00:00 2001
From: Kristianerik <kristian.erik at outlook.com>
Date: Fri, 10 Jul 2026 12:53:11 -0700
Subject: [PATCH] [SROA] Fix assertion failure when promoting self-referential
 load/store

---
 clang/test/Parser/cxx-missing-semi-crash.cpp  |  2 +-
 llvm/lib/Transforms/Utils/SSAUpdater.cpp      |  3 +++
 .../SROA/sroa-self-referential-load.ll        | 20 +++++++++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/SROA/sroa-self-referential-load.ll

diff --git a/clang/test/Parser/cxx-missing-semi-crash.cpp b/clang/test/Parser/cxx-missing-semi-crash.cpp
index bed8a2633a618..a41eda6fc5419 100644
--- a/clang/test/Parser/cxx-missing-semi-crash.cpp
+++ b/clang/test/Parser/cxx-missing-semi-crash.cpp
@@ -10,5 +10,5 @@ void bar() {
   } ::foo<int>; // expected-error {{no template named 'foo' in the global namespace; did you mean simply 'foo'?}} \
                 // expected-error {{template specialization requires 'template<>'}}
 }
-} // namespace N
+} // namespace GH207992
 // expected-error@* {{templates can only be declared in namespace or class scope}}
diff --git a/llvm/lib/Transforms/Utils/SSAUpdater.cpp b/llvm/lib/Transforms/Utils/SSAUpdater.cpp
index b6c5c28161fd8..44afd43ec3896 100644
--- a/llvm/lib/Transforms/Utils/SSAUpdater.cpp
+++ b/llvm/lib/Transforms/Utils/SSAUpdater.cpp
@@ -447,6 +447,9 @@ void LoadAndStorePromoter::run(const SmallVectorImpl<Instruction *> &Insts) {
         // use the stored value.
         if (StoredValue) {
           replaceLoadWithValue(L, StoredValue);
+          // Avoid assertions in unreachable code.
+          if (StoredValue == L)
+            StoredValue = PoisonValue::get(L->getType());
           L->replaceAllUsesWith(StoredValue);
           ReplacedLoads[L] = StoredValue;
         } else {
diff --git a/llvm/test/Transforms/SROA/sroa-self-referential-load.ll b/llvm/test/Transforms/SROA/sroa-self-referential-load.ll
new file mode 100644
index 0000000000000..2d489208e3a1b
--- /dev/null
+++ b/llvm/test/Transforms/SROA/sroa-self-referential-load.ll
@@ -0,0 +1,20 @@
+; RUN: opt --passes=sroa %s -S -o - 2>&1 | FileCheck %s
+
+; Ensure no crash when a store's value operand is the load being promoted,
+; creating a self-referential cycle in unreachable code."
+
+define i32 @func() {
+entry:
+  %a = alloca [2 x i32], align 4
+  br label %loop
+
+loop:
+  br label %loop
+
+exit:
+  store i32 %0, ptr %a, align 4
+  %0 = load i32, ptr %a, align 4
+  br label %exit
+}
+
+; CHECK-LABEL: @func