[GMR] Add a late run of GlobalsModRef to the main pass pipeline behind

the general GMR-in-non-LTO flag.

Without this, we have the global information during the CGSCC pipeline
for GVN and such, but don't have it available during the late loop
optimizations such as the vectorizer. Moreover, after the CGSCC pipeline
has finished we have substantially more accurate and refined call graph
information, function annotations, etc, which will make GMR even more
powerful than it is early in the pipelien.

Note that we have to play silly games with preserving AliasAnalysis
(which is now trivially preserved) in order to let a module analysis
magically be preserved into the entire function pass pipeline.
Simultaneously we have to not make GMR an immutable pass in order to be
able to re-run it and collect fresh data on the final call graph.

llvm-svn: 242999

lib/Transforms/IPO/PassManagerBuilder.cpp

@@ -326,6 +326,24 @@ void PassManagerBuilder::populateModulePassManager(
   // we must insert a no-op module pass to reset the pass manager.
   MPM.add(createBarrierNoopPass());
 
+  if (EnableNonLTOGlobalsModRef)
+    // We add a fresh GlobalsModRef run at this point. This is particularly
+    // useful as the above will have inlined, DCE'ed, and function-attr
+    // propagated everything. We should at this point have a reasonably minimal
+    // and richly annotated call graph. By computing aliasing and mod/ref
+    // information for all local globals here, the late loop passes and notably
+    // the vectorizer will be able to use them to help recognize vectorizable
+    // memory operations.
+    //
+    // Note that this relies on a bug in the pass manager which preserves
+    // a module analysis into a function pass pipeline (and throughout it) so
+    // long as the first function pass doesn't invalidate the module analysis.
+    // Thus both Float2Int and LoopRotate have to preserve AliasAnalysis for
+    // this to work. Fortunately, it is trivial to preserve AliasAnalysis
+    // (doing nothing preserves it as it is required to be conservatively
+    // correct in the face of IR changes).
+    MPM.add(createGlobalsModRefPass());
+
   if (RunFloat2Int)
     MPM.add(createFloat2IntPass());
 

lib/Transforms/Scalar/Float2Int.cpp

@@ -19,6 +19,7 @@
 #include "llvm/ADT/EquivalenceClasses.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/IRBuilder.h"
@@ -60,6 +61,7 @@ namespace {
     bool runOnFunction(Function &F) override;
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.setPreservesCFG();
+      AU.addPreserved<AliasAnalysis>();
     }
 
     void findRoots(Function &F, SmallPtrSet<Instruction*,8> &Roots);

lib/Transforms/Scalar/LoopRotation.cpp

@@ -13,6 +13,7 @@
 
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/CodeMetrics.h"
 #include "llvm/Analysis/InstructionSimplify.h"
@@ -56,6 +57,7 @@ namespace {
 
     // LCSSA form makes instruction renaming easier.
     void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addPreserved<AliasAnalysis>();
       AU.addRequired<AssumptionCacheTracker>();
       AU.addPreserved<DominatorTreeWrapperPass>();
       AU.addRequired<LoopInfoWrapperPass>();