[clang][analysis] Fix flaky clang/test/Analysis/live-stmts.cpp test (#126913)

Multiple people reported flaky bot failures tied to
`clang/test/Analysis/live-stmts.cpp` I tried reproducing the flaky
behavior on my Linux x86_64 system, but the tests appears to be stable
in my context.

Only by looking at the failures reported, I could formulate a potential
diagnosis.
The output always looked almost the same, except that the Exprs dumped
per Basic block were shuffled compared to my expectation. This suggests
to me some ordering issue.

If you look at the backing storage of
`blocksEndToLiveness[B].liveExprs`,
it uses `llvm::ImmutableSet<const Expr *>`.
That container likely uses the pointer values as keys, thus the runtime
values of the addresses influence the iteration order.

To fix this, before dumping, I sort the expressions by their
"beginLocs". It should be efficient enough for a debug checker, where
there is no performance constraint.

This should hopefully fix the flaky behavior on systems where ASLR works
differently than (my) Linux system.

Hopefully fixes #126619
Hopefully fixes #126804

1 files changed, 10 insertions, 1 deletions

diff --git a/clang/lib/Analysis/LiveVariables.cpp b/clang/lib/Analysis/LiveVariables.cpp
index 481932e..af56370 100644
--- a/clang/lib/Analysis/LiveVariables.cpp
+++ b/clang/lib/Analysis/LiveVariables.cpp
@@ -16,7 +16,9 @@
 #include "clang/Analysis/AnalysisDeclContext.h"
 #include "clang/Analysis/CFG.h"
 #include "clang/Analysis/FlowSensitive/DataflowWorklist.h"
+#include "clang/Basic/SourceManager.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <optional>
@@ -662,12 +664,19 @@ void LiveVariables::dumpExprLiveness(const SourceManager &M) {
 }
 
 void LiveVariablesImpl::dumpExprLiveness(const SourceManager &M) {
+  auto ByBeginLoc = [&M](const Expr *L, const Expr *R) {
+    return M.isBeforeInTranslationUnit(L->getBeginLoc(), R->getBeginLoc());
+  };
+
   // Don't iterate over blockEndsToLiveness directly because it's not sorted.
   for (const CFGBlock *B : *analysisContext.getCFG()) {
 
     llvm::errs() << "\n[ B" << B->getBlockID()
                  << " (live expressions at block exit) ]\n";
-    for (const Expr *E : blocksEndToLiveness[B].liveExprs) {
+    std::vector<const Expr *> LiveExprs;
+    llvm::append_range(LiveExprs, blocksEndToLiveness[B].liveExprs);
+    llvm::sort(LiveExprs, ByBeginLoc);
+    for (const Expr *E : LiveExprs) {
       llvm::errs() << "\n";
       E->dump();
     }