[IPO][SampleContextTracker] Use SmallVector to track context profiles to prevent non-determinism.

Use SmallVector instead of SmallSet to track the context profiles mapped. Doing this
can help avoid non-determinism caused by iterating over unordered containers.

This bug was found with reverse iteration turning on,
--extra-llvm-cmake-variables="-DLLVM_REVERSE_ITERATION=ON".
Failing LLVM test profile-context-tracker-debug.ll .

Reviewed By: MaskRay, wenlei

Differential Revision: https://reviews.llvm.org/D99547

Author: huihzhang

llvm/include/llvm/Transforms/IPO/SampleContextTracker.h

@@ -15,7 +15,7 @@
 #ifndef LLVM_TRANSFORMS_IPO_SAMPLECONTEXTTRACKER_H
 #define LLVM_TRANSFORMS_IPO_SAMPLECONTEXTTRACKER_H
 
-#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Analysis/CallGraph.h"
@@ -91,7 +91,7 @@ class ContextTrieNode {
 // calling context and the context is identified by path from root to the node.
 class SampleContextTracker {
 public:
-  using ContextSamplesTy = SmallSet<FunctionSamples *, 16>;
+  using ContextSamplesTy = SmallVector<FunctionSamples *, 16>;
 
   SampleContextTracker(StringMap<FunctionSamples> &Profiles);
   // Query context profile for a specific callee with given name at a given
@@ -144,7 +144,7 @@ class SampleContextTracker {
                                                   StringRef ContextStrToRemove);
 
   // Map from function name to context profiles (excluding base profile)
-  StringMap<ContextSamplesTy> FuncToCtxtProfileSet;
+  StringMap<ContextSamplesTy> FuncToCtxtProfiles;
 
   // Root node for context trie tree
   ContextTrieNode RootContext;

llvm/lib/Transforms/IPO/SampleContextTracker.cpp

@@ -183,7 +183,7 @@ SampleContextTracker::SampleContextTracker(
     SampleContext Context(FuncSample.first(), RawContext);
     LLVM_DEBUG(dbgs() << "Tracking Context for function: " << Context << "\n");
     if (!Context.isBaseContext())
-      FuncToCtxtProfileSet[Context.getNameWithoutContext()].insert(FSamples);
+      FuncToCtxtProfiles[Context.getNameWithoutContext()].push_back(FSamples);
     ContextTrieNode *NewNode = getOrCreateContextPath(Context, true);
     assert(!NewNode->getFunctionSamples() &&
            "New node can't have sample profile");
@@ -268,12 +268,12 @@ SampleContextTracker::getContextSamplesFor(const SampleContext &Context) {
 SampleContextTracker::ContextSamplesTy &
 SampleContextTracker::getAllContextSamplesFor(const Function &Func) {
   StringRef CanonName = FunctionSamples::getCanonicalFnName(Func);
-  return FuncToCtxtProfileSet[CanonName];
+  return FuncToCtxtProfiles[CanonName];
 }
 
 SampleContextTracker::ContextSamplesTy &
 SampleContextTracker::getAllContextSamplesFor(StringRef Name) {
-  return FuncToCtxtProfileSet[Name];
+  return FuncToCtxtProfiles[Name];
 }
 
 FunctionSamples *SampleContextTracker::getBaseSamplesFor(const Function &Func,
@@ -297,7 +297,7 @@ FunctionSamples *SampleContextTracker::getBaseSamplesFor(StringRef Name,
     // We have profile for function under different contexts,
     // create synthetic base profile and merge context profiles
     // into base profile.
-    for (auto *CSamples : FuncToCtxtProfileSet[Name]) {
+    for (auto *CSamples : FuncToCtxtProfiles[Name]) {
       SampleContext &Context = CSamples->getContext();
       ContextTrieNode *FromNode = getContextFor(Context);
       if (FromNode == Node)