From 6cb7d5650054ca5e7d9886e0788ed94db99fafaf Mon Sep 17 00:00:00 2001
From: Adrian Prantl <aprantl@apple.com>
Date: Wed, 29 Jun 2016 15:57:47 -0700
Subject: [PATCH] Cache the previous result of
 IRGenDebugInfo::createInlinedAt().

This saves ~4 seconds of a -r --no-assertions stdlib build and lowers
the contribution of llvm::SourceMgr::getLineAndColumn() to the total
runtime from 6% to 2%.

<rdar://problem/27016577>
---
 lib/IRGen/IRGenDebugInfo.cpp | 17 ++++++++++++++++-
 lib/IRGen/IRGenDebugInfo.h   |  2 ++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/lib/IRGen/IRGenDebugInfo.cpp b/lib/IRGen/IRGenDebugInfo.cpp
index b328c6deb5e58..3d84b716daab8 100644
--- a/lib/IRGen/IRGenDebugInfo.cpp
+++ b/lib/IRGen/IRGenDebugInfo.cpp
@@ -243,7 +243,19 @@ static bool isAbstractClosure(const SILLocation &Loc) {
 llvm::MDNode *IRGenDebugInfo::createInlinedAt(const SILDebugScope *DS) {
   llvm::MDNode *InlinedAt = nullptr;
   if (DS) {
-    for (auto *CS : DS->flattenedInlineTree()) {
+    // The inlined-at chain, starting with the innermost (noninlined) scope.
+    auto Scopes = DS->flattenedInlineTree();
+
+    // See if we share a common prefix with the last chain of inline scopes.
+    unsigned N = 0;
+    while (N < LastInlineChain.size() && N < Scopes.size() &&
+           LastInlineChain[N].first == Scopes[N])
+      InlinedAt = LastInlineChain[N++].second;
+    LastInlineChain.resize(N);
+
+    // Construct the new suffix.
+    for (; N < Scopes.size(); ++N) {
+      auto *CS = Scopes[N];
       // In SIL the inlined-at information is part of the scopes, in
       // LLVM IR it is part of the location. Transforming the inlined-at
       // SIL scope to a location means skipping the inlined-at scope.
@@ -251,6 +263,9 @@ llvm::MDNode *IRGenDebugInfo::createInlinedAt(const SILDebugScope *DS) {
       auto *ParentScope = getOrCreateScope(Parent);
       auto L = CS->Loc.decodeDebugLoc(SM);
       InlinedAt = llvm::DebugLoc::get(L.Line, L.Column, ParentScope, InlinedAt);
+
+      // Cache the suffix.
+      LastInlineChain.push_back({CS, llvm::TrackingMDNodeRef(InlinedAt)});
     }
   }
   return InlinedAt;
diff --git a/lib/IRGen/IRGenDebugInfo.h b/lib/IRGen/IRGenDebugInfo.h
index 465721a13cca6..0841a745d457d 100644
--- a/lib/IRGen/IRGenDebugInfo.h
+++ b/lib/IRGen/IRGenDebugInfo.h
@@ -67,6 +67,8 @@ class IRGenDebugInfo {
   llvm::DenseMap<TypeBase *, llvm::TrackingMDNodeRef> DITypeCache;
   llvm::StringMap<llvm::TrackingMDNodeRef> DIModuleCache;
   TrackingDIRefMap DIRefMap;
+  std::vector<std::pair<const SILDebugScope *, llvm::TrackingMDNodeRef>>
+      LastInlineChain;
 
   llvm::BumpPtrAllocator DebugInfoNames;
   StringRef CWDName;                    /// The current working directory.