[SampleProfile] Fix bug where remapper returns empty string and crashing Sample Profile loader (#71479)

Normally SampleContext does not allow using an empty StirngRef to
construct an object, this is to prevent bugs reading the profile.
However empty names may be emitted by a function which its name is
intentionally set to empty, or a bug in the remapper that returns an
empty string. Regardless, converting it to FunctionId first will prevent
the assert, and that assert check is unnecessary, which will be
addressed in another patch

Author: huangjd

llvm/lib/ProfileData/SampleProfReader.cpp

@@ -1788,8 +1788,11 @@ void SampleProfileReaderItaniumRemapper::applyRemapping(LLVMContext &Ctx) {
 
 std::optional<StringRef>
 SampleProfileReaderItaniumRemapper::lookUpNameInProfile(StringRef Fname) {
-  if (auto Key = Remappings->lookup(Fname))
-    return NameMap.lookup(Key);
+  if (auto Key = Remappings->lookup(Fname)) {
+    StringRef Result = NameMap.lookup(Key);
+    if (!Result.empty())
+      return Result;
+  }
   return std::nullopt;
 }
 

llvm/lib/Transforms/IPO/SampleProfile.cpp

@@ -1630,7 +1630,7 @@ void SampleProfileLoader::promoteMergeNotInlinedContextSamples(
         // separate map so that it does not rehash the original profile.
         if (!OutlineFS)
           OutlineFS = &OutlineFunctionSamples[
-              FunctionSamples::getCanonicalFnName(Callee->getName())];
+              FunctionId(FunctionSamples::getCanonicalFnName(Callee->getName()))];
         OutlineFS->merge(*FS, 1);
         // Set outlined profile to be synthetic to not bias the inliner.
         OutlineFS->SetContextSynthetic();
@@ -2675,12 +2675,12 @@ bool SampleProfileLoader::runOnFunction(Function &F, ModuleAnalysisManager *AM)
     // into base.
     if (!Samples) {
       StringRef CanonName = FunctionSamples::getCanonicalFnName(F);
-      auto It = OutlineFunctionSamples.find(CanonName);
+      auto It = OutlineFunctionSamples.find(FunctionId(CanonName));
       if (It != OutlineFunctionSamples.end()) {
         Samples = &It->second;
       } else if (auto Remapper = Reader->getRemapper()) {
         if (auto RemppedName = Remapper->lookUpNameInProfile(CanonName)) {
-          It = OutlineFunctionSamples.find(*RemppedName);
+          It = OutlineFunctionSamples.find(FunctionId(*RemppedName));
           if (It != OutlineFunctionSamples.end())
             Samples = &It->second;
         }

llvm/test/Transforms/SampleProfile/remap-unmatched.ll

@@ -0,0 +1,8 @@
+; This test should not crash.
+; RUN: opt %s -passes=sample-profile -sample-profile-file=%S/Inputs/remap.prof -sample-profile-remapping-file=%S/Inputs/remap.map
+
+define void @foo() #0 {
+  ret void
+}
+
+attributes #0 = { "use-sample-profile" }