[BasicAA] Cache nonEscapingLocalObjects for alias() calls.

Summary:
Use a small cache for Values tested by nonEscapingLocalObject().
Since the calls to PointerMayBeCaptured are fairly expensive, this saves
a good amount of compile time for anything relying heavily on
BasicAA.alias() calls.

This uses the same approach as the AliasCache, i.e. the cache is reset
after each alias() call. The cache is not used or updated by modRefInfo
calls since it's harder to know when to reset the cache.

Testcases that show improvements with this patch are too large to
include. Example compile time improvement: 7s to 6s.

Reviewers: chandlerc, sunfish

Subscribers: sanjoy, jlebar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57627

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353245 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Analysis/BasicAliasAnalysis.h b/include/llvm/Analysis/BasicAliasAnalysis.h
index d612abc78c5b98880d6167a331a1a42dd4c05da1..29f584cea8eb3131b06e59fe6155248f18595d70 100644 (file)
--- a/include/llvm/Analysis/BasicAliasAnalysis.h
+++ b/include/llvm/Analysis/BasicAliasAnalysis.h
@@ -144,6 +144,8 @@ private:
   using LocPair = std::pair<MemoryLocation, MemoryLocation>;
   using AliasCacheTy = SmallDenseMap<LocPair, AliasResult, 8>;
   AliasCacheTy AliasCache;
+  using IsCapturedCacheTy = SmallDenseMap<const Value *, bool, 8>;
+  IsCapturedCacheTy IsCapturedCache;
 
   /// Tracks phi nodes we have visited.
   ///

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index e3d447885149f20b62c1cd92edca4478e4b52266..382a70b80666a5bde5d4999f391c16566e105fed 100644 (file)
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -116,25 +116,44 @@ bool BasicAAResult::invalidate(Function &Fn, const PreservedAnalyses &PA,
 
 /// Returns true if the pointer is to a function-local object that never
 /// escapes from the function.
-static bool isNonEscapingLocalObject(const Value *V) {
+static bool isNonEscapingLocalObject(
+    const Value *V,
+    SmallDenseMap<const Value *, bool, 8> *IsCapturedCache = nullptr) {
+  SmallDenseMap<const Value *, bool, 8>::iterator CacheIt;
+  if (IsCapturedCache) {
+    bool Inserted;
+    std::tie(CacheIt, Inserted) = IsCapturedCache->insert({V, false});
+    if (!Inserted)
+      // Found cached result, return it!
+      return CacheIt->second;
+  }
+
   // If this is a local allocation, check to see if it escapes.
-  if (isa<AllocaInst>(V) || isNoAliasCall(V))
+  if (isa<AllocaInst>(V) || isNoAliasCall(V)) {
     // Set StoreCaptures to True so that we can assume in our callers that the
     // pointer is not the result of a load instruction. Currently
     // PointerMayBeCaptured doesn't have any special analysis for the
     // StoreCaptures=false case; if it did, our callers could be refined to be
     // more precise.
-    return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
+    auto Ret = !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
+    if (IsCapturedCache)
+      CacheIt->second = Ret;
+    return Ret;
+  }
 
   // If this is an argument that corresponds to a byval or noalias argument,
   // then it has not escaped before entering the function.  Check if it escapes
   // inside the function.
   if (const Argument *A = dyn_cast<Argument>(V))
-    if (A->hasByValAttr() || A->hasNoAliasAttr())
+    if (A->hasByValAttr() || A->hasNoAliasAttr()) {
       // Note even if the argument is marked nocapture, we still need to check
       // for copies made inside the function. The nocapture attribute only
       // specifies that there are no copies made that outlive the function.
-      return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
+      auto Ret = !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
+      if (IsCapturedCache)
+        CacheIt->second = Ret;
+      return Ret;
+    }
 
   return false;
 }
@@ -816,6 +835,7 @@ AliasResult BasicAAResult::alias(const MemoryLocation &LocA,
   // SmallDenseMap if it ever grows larger.
   // FIXME: This should really be shrink_to_inline_capacity_and_clear().
   AliasCache.shrink_and_clear();
+  IsCapturedCache.shrink_and_clear();
   VisitedPhiBBs.clear();
   return Alias;
 }
@@ -1754,9 +1774,9 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
     // temporary store the nocapture argument's value in a temporary memory
     // location if that memory location doesn't escape. Or it may pass a
     // nocapture value to other functions as long as they don't capture it.
-    if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
+    if (isEscapeSource(O1) && isNonEscapingLocalObject(O2, &IsCapturedCache))
       return NoAlias;
-    if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
+    if (isEscapeSource(O2) && isNonEscapingLocalObject(O1, &IsCapturedCache))
       return NoAlias;
   }