Avoid repeated checks and context lookup in llvm::Instruction::getAAMetadata

[serge-sans-paille]

Summary

Repeated call to Instruction::hasMetadata() and lookup in
getContext().pImpl->ValueMetadata are not needed when we always work on
the same instruction, avoid them.

This simple change leads to interesting and consistent speedups in
compile time, around -0.5% according to http://llvm-compile-time-tracker.com, see

http://llvm-compile-time-tracker.com/compare.php?from=9708d88017d0c9adaea65a4f5a5b589b67f292e2&to=88482b9addd5917e9c5226847efeb5451c5f78c0&stat=instructions

for the performance impact.

[nikic]

LGTM

I think given that this lives in Metadata.cpp, the direct access the metadata internals is fine. If there are performance-critical external users of this kind, we could add an API that accepts multiple MDKinds and returns results for all of them.

llvm/lib/IR/Metadata.cpp

1464–1472

interesting -> interested

llvm/lib/IR/Metadata.cpp

if (AppendName)
     Names.push_back(MDB.createString(Name));
 
   MDNode *MD = MDTuple::get(getContext(), Names);
   setMetadata(LLVMContext::MD_annotation, MD);
 }
 
 AAMDNodes Instruction::getAAMetadata() const {
   AAMDNodes Result;
-  Result.TBAA = getMetadata(LLVMContext::MD_tbaa);
-  Result.TBAAStruct = getMetadata(LLVMContext::MD_tbaa_struct);
-  Result.Scope = getMetadata(LLVMContext::MD_alias_scope);
-  Result.NoAlias = getMetadata(LLVMContext::MD_noalias);
+  // Not using Instruction::hasMetadata() because we're not interested in
+  // DebugInfoMetadata.
+  if (Value::hasMetadata()) {
+    const auto &Info = getContext().pImpl->ValueMetadata[this];
+    Result.TBAA = Info.lookup(LLVMContext::MD_tbaa);
+    Result.TBAAStruct = Info.lookup(LLVMContext::MD_tbaa_struct);
+    Result.Scope = Info.lookup(LLVMContext::MD_alias_scope);
+    Result.NoAlias = Info.lookup(LLVMContext::MD_noalias);
+  }
   return Result;
 }
 
 void Instruction::setAAMetadata(const AAMDNodes &N) {
   setMetadata(LLVMContext::MD_tbaa, N.TBAA);
   setMetadata(LLVMContext::MD_tbaa_struct, N.TBAAStruct);
   setMetadata(LLVMContext::MD_alias_scope, N.Scope);
   setMetadata(LLVMContext::MD_noalias, N.NoAlias);