[PATCH] D79969: [LAA] We only need pointer checks if there are non-zero checks (NFC).

[Florian Hahn via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG259abfc7cbc1: [LAA] We only need pointer checks if there are non-zero checks (NFC). (authored by fhahn).

Changed prior to commit:
  https://reviews.llvm.org/D79969?vs=264108&id=266490#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79969/new/

https://reviews.llvm.org/D79969

Files:
  llvm/lib/Analysis/LoopAccessAnalysis.cpp
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp


Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -2795,8 +2795,8 @@
   std::tie(FirstCheckInst, MemRuntimeCheck) =
       addRuntimeChecks(MemCheckBlock->getTerminator(), OrigLoop,
                        RtPtrChecking.getChecks(), RtPtrChecking.getSE());
-  if (!MemRuntimeCheck)
-    return;
+  assert(MemRuntimeCheck && "no RT checks generated although RtPtrChecking "
+                            "claimed checks are required");
 
   if (MemCheckBlock->getParent()->hasOptSize()) {
     assert(Cost->Hints->getForce() == LoopVectorizeHints::FK_Enabled &&
Index: llvm/lib/Analysis/LoopAccessAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -701,12 +701,14 @@
                                      ScalarEvolution *SE, Loop *TheLoop,
                                      const ValueToValueMap &StridesMap,
                                      bool ShouldCheckWrap) {
+  if (!IsRTCheckAnalysisNeeded)
+    return true;
+
   // Find pointers with computable bounds. We are going to use this information
   // to place a runtime bound check.
   bool CanDoRT = true;
 
-  bool NeedRTCheck = false;
-  if (!IsRTCheckAnalysisNeeded) return true;
+  RtCheck.Need = false;
 
   bool IsDepCheckNeeded = isDependencyCheckNeeded();
 
@@ -747,10 +749,10 @@
     // check them.  But there is no need to checks if there is only one
     // dependence set for this alias set.
     //
-    // Note that this function computes CanDoRT and NeedRTCheck independently.
-    // For example CanDoRT=false, NeedRTCheck=false means that we have a pointer
-    // for which we couldn't find the bounds but we don't actually need to emit
-    // any checks so it does not matter.
+    // Note that this function computes CanDoRT and RtCheck.Need independently.
+    // For example CanDoRT=false, RtCheck.Need=false means that we have a
+    // pointer for which we couldn't find the bounds but we don't actually need
+    // to emit any checks so it does not matter.
     bool NeedsAliasSetRTCheck = false;
     if (!(IsDepCheckNeeded && CanDoAliasSetRT && RunningDepId == 2))
       NeedsAliasSetRTCheck = (NumWritePtrChecks >= 2 ||
@@ -773,7 +775,7 @@
     }
 
     CanDoRT &= CanDoAliasSetRT;
-    NeedRTCheck |= NeedsAliasSetRTCheck;
+    RtCheck.Need |= NeedsAliasSetRTCheck;
     ++ASId;
   }
 
@@ -807,15 +809,19 @@
     }
   }
 
-  if (NeedRTCheck && CanDoRT)
+  if (RtCheck.Need && CanDoRT)
     RtCheck.generateChecks(DepCands, IsDepCheckNeeded);
 
   LLVM_DEBUG(dbgs() << "LAA: We need to do " << RtCheck.getNumberOfChecks()
                     << " pointer comparisons.\n");
 
-  RtCheck.Need = NeedRTCheck;
+  // If we can do run-time checks, but there are no checks, no runtime checks
+  // are needed. This can happen when all pointers point to the same underlying
+  // object for example.
+  if (CanDoRT)
+    RtCheck.Need = RtCheck.getNumberOfChecks() != 0;
 
-  bool CanDoRTIfNeeded = !NeedRTCheck || CanDoRT;
+  bool CanDoRTIfNeeded = !RtCheck.Need || CanDoRT;
   if (!CanDoRTIfNeeded)
     RtCheck.reset();
   return CanDoRTIfNeeded;


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