https://github.com/efriedma-quic created
https://github.com/llvm/llvm-project/pull/93115
If a class is empty, don't store it to memory: the store might overwrite useful
data.
(See also d60c3d08.)
Fixes #93040.
>From bdfcc729c309fc5b1092b67d7c3c803c852ae251 Mon Sep 17 00:00:00 2001
From: Eli Friedman <efrie...@quicinc.com>
Date: Wed, 22 May 2024 17:30:41 -0700
Subject: [PATCH] Fix codegen of consteval functions returning an empty class.
If a class is empty, don't store it to memory: the store might overwrite
useful data.
(See also d60c3d08.)
Fixes #93040.
---
clang/lib/CodeGen/CGExprAgg.cpp | 11 +++++++++++
clang/test/CodeGenCXX/cxx2a-consteval.cpp | 24 ++++++++++++++++++++++-
2 files changed, 34 insertions(+), 1 deletion(-)
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index bba00257fd4f0..b1638fa318270 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -135,6 +135,17 @@ class AggExprEmitter : public StmtVisitor<AggExprEmitter> {
EnsureDest(E->getType());
if (llvm::Value *Result = ConstantEmitter(CGF).tryEmitConstantExpr(E)) {
+ // An empty record can overlap other data (if declared with
+ // no_unique_address); omit the store for such types - as there is no
+ // actual data to store.
+ if (CGF.getLangOpts().CPlusPlus) {
+ if (const RecordType *RT = E->getType()->getAs<RecordType>()) {
+ CXXRecordDecl *Record = cast<CXXRecordDecl>(RT->getDecl());
+ if (Record->isEmpty())
+ return;
+ }
+ }
+
Address StoreDest = Dest.getAddress();
// The emitted value is guaranteed to have the same size as the
// destination but can have a different type. Just do a bitcast in this
diff --git a/clang/test/CodeGenCXX/cxx2a-consteval.cpp
b/clang/test/CodeGenCXX/cxx2a-consteval.cpp
index 075cab58358ab..5d5a62f9928fe 100644
--- a/clang/test/CodeGenCXX/cxx2a-consteval.cpp
+++ b/clang/test/CodeGenCXX/cxx2a-consteval.cpp
@@ -1,4 +1,3 @@
-// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
// RUN: %clang_cc1 -emit-llvm %s -std=c++2a -triple x86_64-unknown-linux-gnu
-o %t.ll
// RUN: FileCheck -check-prefix=EVAL -input-file=%t.ll %s
// RUN: FileCheck -check-prefix=EVAL-STATIC -input-file=%t.ll %s
@@ -275,3 +274,26 @@ void f() {
// EVAL-FN: call void @_ZN7GH821542S3C2Ei
}
}
+
+namespace GH93040 {
+struct C { char c = 1; };
+struct Empty { consteval Empty() {} };
+struct Test : C, Empty {
+ [[no_unique_address]] Empty e;
+};
+
+void f() {
+ Test test;
+
+// Make sure we don't overwrite the initialization of c.
+
+// EVAL-FN-LABEL: define {{.*}} void @_ZN7GH930404TestC2Ev
+// EVAL-FN: entry:
+// EVAL-FN-NEXT: [[THIS_ADDR:%.*]] = alloca ptr, align 8
+// EVAL-FN-NEXT: store ptr {{.*}}, ptr [[THIS_ADDR]], align 8
+// EVAL-FN-NEXT: [[THIS:%.*]] = load ptr, ptr [[THIS_ADDR]], align 8
+// EVAL-FN-NEXT: call void @_ZN7GH930401CC2Ev(ptr noundef nonnull align 1
dereferenceable(1) [[THIS]])
+// EVAL-FN-NEXT: %0 = getelementptr inbounds i8, ptr [[THIS]], i64 1
+// EVAL-FN-NEXT: ret void
+}
+}
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