[llvm] r291462 - [LV] Fix-up external IV users after updating dominator tree

[Matthew Simpson via llvm-commits]

Author: mssimpso
Date: Mon Jan  9 13:05:29 2017
New Revision: 291462

URL: http://llvm.org/viewvc/llvm-project?rev=291462&view=rev
Log:
[LV] Fix-up external IV users after updating dominator tree

This patch delays the fix-up step for external induction variable users until
after the dominator tree has been properly updated. This should fix PR30742.
The SCEVExpander in InductionDescriptor::transform can generate code in the
wrong location if the dominator tree is not up-to-date. We should work towards
keeping the dominator tree up-to-date throughout the transformation.

Reference: https://llvm.org/bugs/show_bug.cgi?id=30742
Differential Revision: https://reviews.llvm.org/D28168

Modified:
    llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
    llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll

Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=291462&r1=291461&r2=291462&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Mon Jan  9 13:05:29 2017
@@ -783,6 +783,10 @@ protected:
   // Similarly, we create a new latch condition when setting up the structure
   // of the new loop, so the old one can become dead.
   SmallPtrSet<Instruction *, 4> DeadInstructions;
+
+  // Holds the end values for each induction variable. We save the end values
+  // so we can later fix-up the external users of the induction variables.
+  DenseMap<PHINode *, Value *> IVEndValues;
 };
 
 class InnerLoopUnroller : public InnerLoopVectorizer {
@@ -3417,7 +3421,7 @@ void InnerLoopVectorizer::createEmptyLoo
     // Create phi nodes to merge from the  backedge-taken check block.
     PHINode *BCResumeVal = PHINode::Create(
         OrigPhi->getType(), 3, "bc.resume.val", ScalarPH->getTerminator());
-    Value *EndValue;
+    Value *&EndValue = IVEndValues[OrigPhi];
     if (OrigPhi == OldInduction) {
       // We know what the end value is.
       EndValue = CountRoundDown;
@@ -3436,9 +3440,6 @@ void InnerLoopVectorizer::createEmptyLoo
     // or the value at the end of the vectorized loop.
     BCResumeVal->addIncoming(EndValue, MiddleBlock);
 
-    // Fix up external users of the induction variable.
-    fixupIVUsers(OrigPhi, II, CountRoundDown, EndValue, MiddleBlock);
-
     // Fix the scalar body counter (PHI node).
     unsigned BlockIdx = OrigPhi->getBasicBlockIndex(ScalarPH);
 
@@ -4109,11 +4110,23 @@ void InnerLoopVectorizer::vectorizeLoop(
     Phi->setIncomingValue(IncomingEdgeBlockIdx, LoopExitInst);
   } // end of for each Phi in PHIsToFix.
 
-  fixLCSSAPHIs();
-
-  // Make sure DomTree is updated.
+  // Update the dominator tree.
+  //
+  // FIXME: After creating the structure of the new loop, the dominator tree is
+  //        no longer up-to-date, and it remains that way until we update it
+  //        here. An out-of-date dominator tree is problematic for SCEV,
+  //        because SCEVExpander uses it to guide code generation. The
+  //        vectorizer use SCEVExpanders in several places. Instead, we should
+  //        keep the dominator tree up-to-date as we go.
   updateAnalysis();
 
+  // Fix-up external users of the induction variables.
+  for (auto &Entry : *Legal->getInductionVars())
+    fixupIVUsers(Entry.first, Entry.second,
+                 getOrCreateVectorTripCount(LI->getLoopFor(LoopVectorBody)),
+                 IVEndValues[Entry.first], LoopMiddleBlock);
+
+  fixLCSSAPHIs();
   predicateInstructions();
 
   // Remove redundant induction instructions.

Modified: llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll?rev=291462&r1=291461&r2=291462&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll Mon Jan  9 13:05:29 2017
@@ -133,3 +133,48 @@ for.end:
   store i32 %phi2, i32* %p
   ret i32 %phi
 }
+
+; CHECK-LABEL: @PR30742
+; CHECK: min.iters.checked
+; CHECK:   %[[N_MOD_VF:.+]] = urem i32 %[[T5:.+]], 2
+; CHECK:   %[[N_VEC:.+]] = sub i32 %[[T5]], %[[N_MOD_VF]]
+; CHECK: middle.block
+; CHECK:   %[[CMP:.+]] = icmp eq i32 %[[T5]], %[[N_VEC]]
+; CHECK:   %[[T15:.+]] = add i32 %tmp03, -7
+; CHECK:   %[[T16:.+]] = shl i32 %[[N_MOD_VF]], 3
+; CHECK:   %[[T17:.+]] = add i32 %[[T15]], %[[T16]]
+; CHECK:   %[[T18:.+]] = shl i32 {{.*}}, 3
+; CHECK:   %ind.escape = sub i32 %[[T17]], %[[T18]]
+; CHECK:   br i1 %[[CMP]], label %BB3, label %scalar.ph
+define void @PR30742() {
+BB0:
+  br label %BB1
+
+BB1:
+  %tmp00 = load i32, i32* undef, align 16
+  %tmp01 = sub i32 %tmp00, undef
+  %tmp02 = icmp slt i32 %tmp01, 1
+  %tmp03 = select i1 %tmp02, i32 1, i32 %tmp01
+  %tmp04 = add nsw i32 %tmp03, -7
+  br label %BB2
+
+BB2:
+  %tmp05 = phi i32 [ %tmp04, %BB1 ], [ %tmp06, %BB2 ]
+  %tmp06 = add i32 %tmp05, -8
+  %tmp07 = icmp sgt i32 %tmp06, 0
+  br i1 %tmp07, label %BB2, label %BB3
+
+BB3:
+  %tmp08 = phi i32 [ %tmp05, %BB2 ]
+  %tmp09 = sub i32 %tmp00, undef
+  %tmp10 = icmp slt i32 %tmp09, 1
+  %tmp11 = select i1 %tmp10, i32 1, i32 %tmp09
+  %tmp12 = add nsw i32 %tmp11, -7
+  br label %BB4
+
+BB4:
+  %tmp13 = phi i32 [ %tmp12, %BB3 ], [ %tmp14, %BB4 ]
+  %tmp14 = add i32 %tmp13, -8
+  %tmp15 = icmp sgt i32 %tmp14, 0
+  br i1 %tmp15, label %BB4, label %BB1
+}