From 3a54b6a4b71c21cf3bab4f132cbc2904fb9d997e Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Thu, 25 Jun 2020 21:35:41 +0200
Subject: [PATCH] [MemDep] Use BatchAA when computing pointer dependencies

We're not changing IR while running a single MemDep query, so it's
safe to cache alias analysis results using BatchAA. This adds BatchAA
usage to getSimplePointerDependencyFrom(), which is non-intrusive --
covering larger parts (like a whole processNonLocalLoad query) is
also possible, but requires threading BatchAA through a bunch of APIs.

For the ThinLTO configuration, this is a 1% geomean improvement on CTMark.

Differential Revision: https://reviews.llvm.org/D85583
---
 llvm/lib/Analysis/MemoryDependenceAnalysis.cpp | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 7f3de0f..2428d57 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -362,6 +362,8 @@ MemoryDependenceResults::getInvariantGroupPointerDependency(LoadInst *LI,
 MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
     const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt,
     BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) {
+  // We can batch AA queries, because IR does not change during a MemDep query.
+  BatchAAResults BatchAA(AA);
   bool isInvariantLoad = false;
 
   unsigned DefaultLimit = getDefaultBlockScanLimit();
@@ -445,7 +447,7 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
         // pointer, not on query pointers that are indexed off of them.  It'd
         // be nice to handle that at some point (the right approach is to use
         // GetPointerBaseWithConstantOffset).
-        if (AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), MemLoc))
+        if (BatchAA.isMustAlias(MemoryLocation(II->getArgOperand(1)), MemLoc))
           return MemDepResult::getDef(II);
         continue;
       }
@@ -485,7 +487,7 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
       MemoryLocation LoadLoc = MemoryLocation::get(LI);
 
       // If we found a pointer, check if it could be the same as our pointer.
-      AliasResult R = AA.alias(LoadLoc, MemLoc);
+      AliasResult R = BatchAA.alias(LoadLoc, MemLoc);
 
       if (isLoad) {
         if (R == NoAlias)
@@ -516,7 +518,7 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
         continue;
 
       // Stores don't alias loads from read-only memory.
-      if (AA.pointsToConstantMemory(LoadLoc))
+      if (BatchAA.pointsToConstantMemory(LoadLoc))
         continue;
 
       // Stores depend on may/must aliased loads.
@@ -547,7 +549,7 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
       // If alias analysis can tell that this store is guaranteed to not modify
       // the query pointer, ignore it.  Use getModRefInfo to handle cases where
       // the query pointer points to constant memory etc.
-      if (!isModOrRefSet(AA.getModRefInfo(SI, MemLoc)))
+      if (!isModOrRefSet(BatchAA.getModRefInfo(SI, MemLoc)))
         continue;
 
       // Ok, this store might clobber the query pointer.  Check to see if it is
@@ -556,7 +558,7 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
       MemoryLocation StoreLoc = MemoryLocation::get(SI);
 
       // If we found a pointer, check if it could be the same as our pointer.
-      AliasResult R = AA.alias(StoreLoc, MemLoc);
+      AliasResult R = BatchAA.alias(StoreLoc, MemLoc);
 
       if (R == NoAlias)
         continue;
@@ -575,7 +577,7 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
     // handled by BasicAA.
     if (isa<AllocaInst>(Inst) || isNoAliasFn(Inst, &TLI)) {
       const Value *AccessPtr = getUnderlyingObject(MemLoc.Ptr);
-      if (AccessPtr == Inst || AA.isMustAlias(Inst, AccessPtr))
+      if (AccessPtr == Inst || BatchAA.isMustAlias(Inst, AccessPtr))
         return MemDepResult::getDef(Inst);
     }
 
@@ -592,9 +594,10 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
         continue;
 
     // See if this instruction (e.g. a call or vaarg) mod/ref's the pointer.
-    ModRefInfo MR = AA.getModRefInfo(Inst, MemLoc);
+    ModRefInfo MR = BatchAA.getModRefInfo(Inst, MemLoc);
     // If necessary, perform additional analysis.
     if (isModAndRefSet(MR))
+      // TODO: Support callCapturesBefore() on BatchAAResults.
       MR = AA.callCapturesBefore(Inst, MemLoc, &DT);
     switch (clearMust(MR)) {
     case ModRefInfo::NoModRef:
-- 
2.7.4