From 1ab487fdc7da348fea52b2f665bdff433a63b136 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Mon, 5 Jan 2015 12:32:11 +0000
Subject: [PATCH] [PM] Don't run the machinery of invalidating all the analysis
 passes when all are being preserved.

We want to short-circuit this for a couple of reasons. One, I don't
really want passes to grow a dependency on actually receiving their
invalidate call when they've been preserved. I'm thinking about removing
this entirely. But more importantly, preserving everything is likely to
be the common case in a lot of scenarios, and it would be really good to
bypass all of the invalidation and preservation machinery there.
Avoiding calling N opaque functions to try to invalidate things that are
by definition still valid seems important. =]

This wasn't really inpsired by much other than seeing the spam in the
logging for analyses, but it seems better ot get it checked in rather
than forgetting about it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225163 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/IR/PassManager.h     | 12 ++++++++----
 lib/Analysis/CGSCCPassManager.cpp |  4 ++++
 lib/IR/PassManager.cpp            |  8 ++++++++
 test/Other/new-pass-manager.ll    |  7 +++++++
 4 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/include/llvm/IR/PassManager.h b/include/llvm/IR/PassManager.h
index b2bf73ffe8b..59855b5fc91 100644
--- a/include/llvm/IR/PassManager.h
+++ b/include/llvm/IR/PassManager.h
@@ -141,15 +141,19 @@ public:
            PreservedPassIDs.count(PassID);
   }
 
+  /// \brief Test whether all passes are preserved.
+  ///
+  /// This is used primarily to optimize for the case of no changes which will
+  /// common in many scenarios.
+  bool areAllPreserved() const {
+    return PreservedPassIDs.count((void *)AllPassesID);
+  }
+
 private:
   // Note that this must not be -1 or -2 as those are already used by the
   // SmallPtrSet.
   static const uintptr_t AllPassesID = (intptr_t)(-3);
 
-  bool areAllPreserved() const {
-    return PreservedPassIDs.count((void *)AllPassesID);
-  }
-
   SmallPtrSet<void *, 2> PreservedPassIDs;
 };
 
diff --git a/lib/Analysis/CGSCCPassManager.cpp b/lib/Analysis/CGSCCPassManager.cpp
index 4d569a972fe..ad7eea8efca 100644
--- a/lib/Analysis/CGSCCPassManager.cpp
+++ b/lib/Analysis/CGSCCPassManager.cpp
@@ -92,6 +92,10 @@ void CGSCCAnalysisManager::invalidateImpl(void *PassID, LazyCallGraph::SCC &C) {
 
 void CGSCCAnalysisManager::invalidateImpl(LazyCallGraph::SCC &C,
                                           const PreservedAnalyses &PA) {
+  // Short circuit for a common case of all analyses being preserved.
+  if (PA.areAllPreserved())
+    return;
+
   if (DebugPM)
     dbgs() << "Invalidating all non-preserved analyses for SCC: " << C.getName()
            << "\n";
diff --git a/lib/IR/PassManager.cpp b/lib/IR/PassManager.cpp
index c7638bb7fce..1eab4ae19bf 100644
--- a/lib/IR/PassManager.cpp
+++ b/lib/IR/PassManager.cpp
@@ -78,6 +78,10 @@ void ModuleAnalysisManager::invalidateImpl(void *PassID, Module &M) {
 
 void ModuleAnalysisManager::invalidateImpl(Module &M,
                                            const PreservedAnalyses &PA) {
+  // Short circuit for a common case of all analyses being preserved.
+  if (PA.areAllPreserved())
+    return;
+
   if (DebugPM)
     dbgs() << "Invalidating all non-preserved analyses for module: "
            << M.getModuleIdentifier() << "\n";
@@ -176,6 +180,10 @@ void FunctionAnalysisManager::invalidateImpl(void *PassID, Function &F) {
 
 void FunctionAnalysisManager::invalidateImpl(Function &F,
                                              const PreservedAnalyses &PA) {
+  // Short circuit for a common case of all analyses being preserved.
+  if (PA.areAllPreserved())
+    return;
+
   if (DebugPM)
     dbgs() << "Invalidating all non-preserved analyses for function: "
            << F.getName() << "\n";
diff --git a/test/Other/new-pass-manager.ll b/test/Other/new-pass-manager.ll
index f9fc444dbf1..bb338d42253 100644
--- a/test/Other/new-pass-manager.ll
+++ b/test/Other/new-pass-manager.ll
@@ -94,6 +94,13 @@
 ; CHECK-LCG-ANALYSIS: Running module analysis: Lazy CallGraph Analysis
 ; CHECK-LCG-ANALYSIS: Starting CGSCC pass manager run.
 
+; Make sure no-op passes that preserve all analyses don't even try to do any
+; analysis invalidation.
+; RUN: opt -disable-output -debug-pass-manager -debug-cgscc-pass-manager -passes='cgscc(function(no-op-function))' %s 2>&1 \
+; RUN:     | FileCheck %s --check-prefix=CHECK-NO-OP-INVALIDATION
+; CHECK-NO-OP-INVALIDATION: Starting module pass manager
+; CHECK-NO-OP-INVALIDATION-NOT: Invalidating all non-preserved analyses
+
 define void @foo() {
   ret void
 }
-- 
2.34.1