From c320ed14d22f300f001662cd8c3d1538524f0e25 Mon Sep 17 00:00:00 2001
From: Adam Nemet <anemet@apple.com>
Date: Tue, 10 Mar 2015 18:54:23 +0000
Subject: [PATCH] [LAA-memchecks 2/3] Move number of memcheck threshold
 checking to LV

Now the analysis won't "fail" if the memchecks exceed the threshold.  It
is the transform pass' responsibility to perform the check.

This allows the transform pass to further analyze/eliminate the
memchecks.  E.g. in Loop distribution we only need to check pointers
that end up in different partitions.

Note that there is a slight change of functionality here.  The logic in
analyzeLoop is that if dependence checking fails due to non-constant
distance between the pointers, another attempt is made to prove safety
of the dependences purely using run-time checks.

Before this patch we could fail the loop due to exceeding the memcheck
threshold after the first step, now we only check the threshold in the
client after the full analysis.  There is no measurable compile-time
effect but I wanted to record this here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231817 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Analysis/LoopAccessAnalysis.h |  8 ++++++++
 lib/Analysis/LoopAccessAnalysis.cpp        | 30 +++---------------------------
 lib/Transforms/Vectorize/LoopVectorize.cpp | 14 +++++++++++++-
 3 files changed, 24 insertions(+), 28 deletions(-)

diff --git a/include/llvm/Analysis/LoopAccessAnalysis.h b/include/llvm/Analysis/LoopAccessAnalysis.h
index 31b0b8eb21d..d188327fbf4 100644
--- a/include/llvm/Analysis/LoopAccessAnalysis.h
+++ b/include/llvm/Analysis/LoopAccessAnalysis.h
@@ -362,6 +362,10 @@ public:
     return &PtrRtCheck;
   }
 
+  /// \brief Number of memchecks required to prove independence of otherwise
+  /// may-alias pointers.
+  unsigned getNumRuntimePointerChecks() const { return NumComparisons; }
+
   /// Return true if the block BB needs to be predicated in order for the loop
   /// to be vectorized.
   static bool blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
@@ -416,6 +420,10 @@ private:
   /// loop-independent and loop-carried dependences between memory accesses.
   MemoryDepChecker DepChecker;
 
+  /// \brief Number of memchecks required to prove independence of otherwise
+  /// may-alias pointers
+  unsigned NumComparisons;
+
   Loop *TheLoop;
   ScalarEvolution *SE;
   const DataLayout &DL;
diff --git a/lib/Analysis/LoopAccessAnalysis.cpp b/lib/Analysis/LoopAccessAnalysis.cpp
index 27ccd66541f..d044bb008e9 100644
--- a/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1072,7 +1072,6 @@ void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) {
 
   // Find pointers with computable bounds. We are going to use this information
   // to place a runtime bound check.
-  unsigned NumComparisons = 0;
   bool CanDoRT = false;
   if (NeedRTCheck)
     CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop,
@@ -1098,17 +1097,6 @@ void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) {
     return;
   }
 
-  if (NumComparisons > RuntimeMemoryCheckThreshold) {
-    emitAnalysis(LoopAccessReport()
-                 << NumComparisons << " exceeds limit of "
-                 << RuntimeMemoryCheckThreshold
-                 << " dependent memory operations checked at runtime");
-    DEBUG(dbgs() << "LAA: Too many memory checks needed.\n");
-    PtrRtCheck.reset();
-    CanVecMem = false;
-    return;
-  }
-
   PtrRtCheck.Need = NeedRTCheck;
 
   CanVecMem = true;
@@ -1140,18 +1128,6 @@ void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) {
         return;
       }
 
-      // Check that we did not collect too many pointers.
-      if (NumComparisons > RuntimeMemoryCheckThreshold) {
-        emitAnalysis(LoopAccessReport()
-                     << NumComparisons << " exceeds limit of "
-                     << RuntimeMemoryCheckThreshold
-                     << " dependent memory operations checked at runtime");
-        DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n");
-        PtrRtCheck.reset();
-        CanVecMem = false;
-        return;
-      }
-
       CanVecMem = true;
     }
   }
@@ -1283,9 +1259,9 @@ LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
                                const TargetLibraryInfo *TLI, AliasAnalysis *AA,
                                DominatorTree *DT,
                                const ValueToValueMap &Strides)
-    : DepChecker(SE, L), TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA),
-      DT(DT), NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1U),
-      CanVecMem(false) {
+    : DepChecker(SE, L), NumComparisons(0), TheLoop(L), SE(SE), DL(DL),
+      TLI(TLI), AA(AA), DT(DT), NumLoads(0), NumStores(0),
+      MaxSafeDepDistBytes(-1U), CanVecMem(false) {
   if (canAnalyzeLoop())
     analyzeLoop(Strides);
 }
diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index 18a456f611a..1abefd75c97 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -3874,7 +3874,19 @@ bool LoopVectorizationLegality::canVectorizeMemory() {
   auto &OptionalReport = LAI->getReport();
   if (OptionalReport)
     emitAnalysis(VectorizationReport(*OptionalReport));
-  return LAI->canVectorizeMemory();
+  if (!LAI->canVectorizeMemory())
+    return false;
+
+  if (LAI->getNumRuntimePointerChecks() >
+      VectorizerParams::RuntimeMemoryCheckThreshold) {
+    emitAnalysis(VectorizationReport()
+                 << LAI->getNumRuntimePointerChecks() << " exceeds limit of "
+                 << VectorizerParams::RuntimeMemoryCheckThreshold
+                 << " dependent memory operations checked at runtime");
+    DEBUG(dbgs() << "LV: Too many memory checks needed.\n");
+    return false;
+  }
+  return true;
 }
 
 static bool hasMultipleUsesOf(Instruction *I,
-- 
2.11.0