LoopDistribute/LAA: Respect convergent

This case is slightly tricky, because loop distribution should be
allowed in some cases, and not others. As long as runtime dependency
checks don't need to be introduced, this should be OK. This is further
complicated by the fact that LoopDistribute partially ignores if LAA
says that vectorization is safe, and then does its own runtime pointer
legality checks.

Note this pass still does not handle noduplicate correctly, as this
should always be forbidden with it. I'm not going to bother trying to
fix it, as it would require more effort and I think noduplicate should
be removed.

https://reviews.llvm.org/D62607

llvm-svn: 363160

1 files changed, 55 insertions, 9 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index d6fbf6f2827..36bd9a8b7ea 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1778,6 +1778,11 @@ void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
   unsigned NumReads = 0;
   unsigned NumReadWrites = 0;
 
+  bool HasComplexMemInst = false;
+
+  // A runtime check is only legal to insert if there are no convergent calls.
+  HasConvergentOp = false;
+
   PtrRtChecking->Pointers.clear();
   PtrRtChecking->Need = false;
 
@@ -1785,8 +1790,25 @@ void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
 
   // For each block.
   for (BasicBlock *BB : TheLoop->blocks()) {
-    // Scan the BB and collect legal loads and stores.
+    // Scan the BB and collect legal loads and stores. Also detect any
+    // convergent instructions.
     for (Instruction &I : *BB) {
+      if (auto *Call = dyn_cast<CallBase>(&I)) {
+        if (Call->isConvergent())
+          HasConvergentOp = true;
+      }
+
+      // With both a non-vectorizable memory instruction and a convergent
+      // operation, found in this loop, no reason to continue the search.
+      if (HasComplexMemInst && HasConvergentOp) {
+        CanVecMem = false;
+        return;
+      }
+
+      // Avoid hitting recordAnalysis multiple times.
+      if (HasComplexMemInst)
+        continue;
+
       // If this is a load, save it. If this instruction can read from memory
       // but is not a load, then we quit. Notice that we don't handle function
       // calls that read or write.
@@ -1805,12 +1827,18 @@ void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
           continue;
 
         auto *Ld = dyn_cast<LoadInst>(&I);
-        if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) {
+        if (!Ld) {
+          recordAnalysis("CantVectorizeInstruction", Ld)
+            << "instruction cannot be vectorized";
+          HasComplexMemInst = true;
+          continue;
+        }
+        if (!Ld->isSimple() && !IsAnnotatedParallel) {
           recordAnalysis("NonSimpleLoad", Ld)
               << "read with atomic ordering or volatile read";
           LLVM_DEBUG(dbgs() << "LAA: Found a non-simple load.\n");
-          CanVecMem = false;
-          return;
+          HasComplexMemInst = true;
+          continue;
         }
         NumLoads++;
         Loads.push_back(Ld);
@@ -1826,15 +1854,15 @@ void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
         if (!St) {
           recordAnalysis("CantVectorizeInstruction", St)
               << "instruction cannot be vectorized";
-          CanVecMem = false;
-          return;
+          HasComplexMemInst = true;
+          continue;
         }
         if (!St->isSimple() && !IsAnnotatedParallel) {
           recordAnalysis("NonSimpleStore", St)
               << "write with atomic ordering or volatile write";
           LLVM_DEBUG(dbgs() << "LAA: Found a non-simple store.\n");
-          CanVecMem = false;
-          return;
+          HasComplexMemInst = true;
+          continue;
         }
         NumStores++;
         Stores.push_back(St);
@@ -1845,6 +1873,11 @@ void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
     } // Next instr.
   } // Next block.
 
+  if (HasComplexMemInst) {
+    CanVecMem = false;
+    return;
+  }
+
   // Now we have two lists that hold the loads and the stores.
   // Next, we find the pointers that they use.
 
@@ -1962,7 +1995,7 @@ void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
   }
 
   LLVM_DEBUG(
-      dbgs() << "LAA: We can perform a memory runtime check if needed.\n");
+    dbgs() << "LAA: May be able to perform a memory runtime check if needed.\n");
 
   CanVecMem = true;
   if (Accesses.isDependencyCheckNeeded()) {
@@ -1997,6 +2030,15 @@ void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
     }
   }
 
+  if (HasConvergentOp) {
+    recordAnalysis("CantInsertRuntimeCheckWithConvergent")
+      << "cannot add control dependency to convergent operation";
+    LLVM_DEBUG(dbgs() << "LAA: We can't vectorize because a runtime check "
+                         "would be needed with a convergent operation\n");
+    CanVecMem = false;
+    return;
+  }
+
   if (CanVecMem)
     LLVM_DEBUG(
         dbgs() << "LAA: No unsafe dependent memory operations in loop.  We"
@@ -2285,6 +2327,7 @@ LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
       PtrRtChecking(llvm::make_unique<RuntimePointerChecking>(SE)),
       DepChecker(llvm::make_unique<MemoryDepChecker>(*PSE, L)), TheLoop(L),
       NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1), CanVecMem(false),
+      HasConvergentOp(false),
       HasDependenceInvolvingLoopInvariantAddress(false) {
   if (canAnalyzeLoop())
     analyzeLoop(AA, LI, TLI, DT);
@@ -2301,6 +2344,9 @@ void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
     OS << "\n";
   }
 
+  if (HasConvergentOp)
+    OS.indent(Depth) << "Has convergent operation in loop\n";
+
   if (Report)
     OS.indent(Depth) << "Report: " << Report->getMsg() << "\n";