[gnu-objc] Make selector order deterministic.

Summary:
This probably fixes PR35277, though there may be other sources of
nondeterminism (this was the only case of iterating over a DenseMap).

It's difficult to provide a test case for this, because it shows up only
on systems with ASLR enabled.

Reviewers: rjmccall

Reviewed By: rjmccall

Subscribers: bmwiedemann, mgrang, cfe-commits

Differential Revision: https://reviews.llvm.org/D50559

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@339668 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 23 insertions, 3 deletions

diff --git a/lib/CodeGen/CGObjCGNU.cpp b/lib/CodeGen/CGObjCGNU.cpp
index 622c8bfb50..b509187b4c 100644
--- a/lib/CodeGen/CGObjCGNU.cpp
+++ b/lib/CodeGen/CGObjCGNU.cpp
@@ -3541,12 +3541,16 @@ llvm::Function *CGObjCGNU::ModuleInitFunction() {
     ConstantInitBuilder builder(CGM);
     auto selectors = builder.beginArray(selStructTy);
     auto &table = SelectorTable; // MSVC workaround
-    for (auto &entry : table) {
+    std::vector<Selector> allSelectors;
+    for (auto &entry : table)
+      allSelectors.push_back(entry.first);
+    llvm::sort(allSelectors.begin(), allSelectors.end());
 
-      std::string selNameStr = entry.first.getAsString();
+    for (auto &untypedSel : allSelectors) {
+      std::string selNameStr = untypedSel.getAsString();
       llvm::Constant *selName = ExportUniqueString(selNameStr, ".objc_sel_name");
 
-      for (TypedSelector &sel : entry.second) {
+      for (TypedSelector &sel : table[untypedSel]) {
         llvm::Constant *selectorTypeEncoding = NULLPtr;
         if (!sel.first.empty())
           selectorTypeEncoding =
diff --git a/test/CodeGenObjC/gnu-deterministic-selectors.m b/test/CodeGenObjC/gnu-deterministic-selectors.m
new file mode 100644
index 0000000000..5f8d2e5378
--- /dev/null
+++ b/test/CodeGenObjC/gnu-deterministic-selectors.m
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-freebsd -fobjc-runtime=gnustep-1.5 %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-freebsd -fobjc-runtime=gcc %s -emit-llvm -o - | FileCheck %s
+
+// Check that these selectors are emitted in alphabetical order.
+// The order doesn't actually matter, only that it doesn't vary across runs.
+// Clang sorts them when targeting a GCC-like ABI to guarantee determinism.
+// CHECK: @.objc_selector_list = internal global [6 x { i8*, i8* }] [{ i8*, i8* } { i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.objc_sel_namea, i64 0, i64 0), i8* null }, { i8*, i8* } { i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.objc_sel_nameg, i64 0, i64 0), i8* null }, { i8*, i8* } { i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.objc_sel_namej, i64 0, i64 0), i8* null }, { i8*, i8* } { i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.objc_sel_namel, i64 0, i64 0), i8* null }, { i8*, i8* } { i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.objc_sel_namez, i64 0, i64 0), i8* null }, { i8*, i8* } zeroinitializer], align 8
+
+
+void f() {
+	SEL a = @selector(z);
+	SEL b = @selector(a);
+	SEL c = @selector(g);
+	SEL d = @selector(l);
+	SEL e = @selector(j);
+}