[LV] Teach about non header phis that have uses outside the loop

Summary:
This patch teaches the loop vectorizer to vectorize loops with non
header phis that have have outside uses.  This is because the iteration
dependence distance for these phis can be widened upto VF (similar to
how we do for induction/reduction) if they do not have a cyclic
dependence with header phis. When identifying reduction/induction/first
order recurrence header phis, we already identify if there are any cyclic
dependencies that prevents vectorization.

The vectorizer is taught to extract the last element from the vectorized
phi and update the scalar loop exit block phi to contain this extracted
element from the vector loop.

This patch can be extended to vectorize loops where instructions other
than phis have outside uses.

Reviewers: Ayal, mkuper, mssimpso, efriedma

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D50579

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339703 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 697bc1b..97a61bd 100644 (file)
--- a/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -434,8 +434,10 @@ static Type *getWiderType(const DataLayout &DL, Type *Ty0, Type *Ty1) {
 /// identified reduction variable.
 static bool hasOutsideLoopUser(const Loop *TheLoop, Instruction *Inst,
                                SmallPtrSetImpl<Value *> &AllowedExit) {
-  // Reduction and Induction instructions are allowed to have exit users. All
+  // Reductions, Inductions and non-header phis are allowed to have exit users. All
   // other instructions must not have external users.
+  // TODO: Non-phi instructions can also be taught to have exit users, now that
+  // we know how to extract the last scalar element from the loop.
   if (!AllowedExit.count(Inst))
     // Check that all of the users of the loop are inside the BB.
     for (User *U : Inst->users()) {
@@ -597,14 +599,12 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
         // can convert it to select during if-conversion. No need to check if
         // the PHIs in this block are induction or reduction variables.
         if (BB != Header) {
-          // Check that this instruction has no outside users or is an
-          // identified reduction value with an outside user.
-          if (!hasOutsideLoopUser(TheLoop, Phi, AllowedExit))
-            continue;
-          ORE->emit(createMissedAnalysis("NeitherInductionNorReduction", Phi)
-                    << "value could not be identified as "
-                       "an induction or reduction variable");
-          return false;
+          // Non-header phi nodes that have outside uses can be vectorized. Add
+          // them to the list of allowed exits.
+          // Unsafe cyclic dependencies with header phis are identified during
+          // legalization for reduction, induction and first order
+          // recurrences.
+          continue;
         }
 
         // We only allow if-converted PHIs with exactly two incoming values.

diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index 859d0c9..237c033 100644 (file)
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -3720,9 +3720,13 @@ void InnerLoopVectorizer::fixReduction(PHINode *Phi) {
 void InnerLoopVectorizer::fixLCSSAPHIs() {
   for (PHINode &LCSSAPhi : LoopExitBlock->phis()) {
     if (LCSSAPhi.getNumIncomingValues() == 1) {
-      assert(OrigLoop->isLoopInvariant(LCSSAPhi.getIncomingValue(0)) &&
-             "Incoming value isn't loop invariant");
-      LCSSAPhi.addIncoming(LCSSAPhi.getIncomingValue(0), LoopMiddleBlock);
+      auto *IncomingValue = LCSSAPhi.getIncomingValue(0);
+      // Can be a loop invariant incoming value or the last scalar value to be
+      // extracted from the vectorized loop.
+      Builder.SetInsertPoint(LoopMiddleBlock->getTerminator());
+      Value *lastIncomingValue =
+          getOrCreateScalarValue(IncomingValue, {UF - 1, VF - 1});
+      LCSSAPhi.addIncoming(lastIncomingValue, LoopMiddleBlock);
     }
   }
 }

diff --git a/test/Transforms/LoopVectorize/no_outside_user.ll b/test/Transforms/LoopVectorize/no_outside_user.ll
index 39363f6..d0b5d7c 100644 (file)
--- a/test/Transforms/LoopVectorize/no_outside_user.ll
+++ b/test/Transforms/LoopVectorize/no_outside_user.ll
@@ -1,7 +1,5 @@
 ; RUN: opt -S -loop-vectorize -force-vector-interleave=1 -force-vector-width=2 < %s 2>&1 | FileCheck %s
 
-; CHECK: remark: {{.*}}: loop not vectorized: value could not be identified as an induction or reduction variable
-
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32-S128"
 
 @f = common global i32 0, align 4
@@ -11,13 +9,22 @@ target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f3
 @b = common global i32 0, align 4
 @e = common global i32 0, align 4
 
-; We used to vectorize this loop. But it has a value that is used outside of the
+; It has a value that is used outside of the loop
 ; and is not a recognized reduction variable "tmp17".
+; However, tmp17 is a non-header phi which is an allowed exit.
 
-; CHECK-LABEL: @main(
-; CHECK-NOT: <2 x i32>
+; CHECK-LABEL: @test1(
+; CHECK: %vec.ind = phi <2 x i32>
+; CHECK: [[CMP:%[a-zA-Z0-9.]+]] = icmp sgt <2 x i32> %vec.ind, <i32 10, i32 10>
+; CHECK: %predphi = select <2 x i1> [[CMP]], <2 x i32> <i32 1, i32 1>, <2 x i32> zeroinitializer
+
+; CHECK-LABEL: middle.block:
+; CHECK:          [[E1:%[a-zA-Z0-9.]+]] = extractelement <2 x i32> %predphi, i32 1
+
+; CHECK-LABEL: f1.exit.loopexit:
+; CHECK:          %.lcssa = phi i32 [ %tmp17, %bb16 ], [ [[E1]], %middle.block ]
 
-define i32 @main()  {
+define i32 @test1()  {
 bb:
   %b.promoted = load i32, i32* @b, align 4
   br label %.lr.ph.i
@@ -40,3 +47,221 @@ f1.exit.loopexit:
   %.lcssa = phi i32 [ %tmp17, %bb16 ]
   ret i32 %.lcssa
 }
+
+; non-hdr phi depends on header phi.
+; CHECK-LABEL: @test2(
+; CHECK: %vec.ind = phi <2 x i32>
+; CHECK: [[CMP:%[a-zA-Z0-9.]+]] = icmp sgt <2 x i32> %vec.ind, <i32 10, i32 10>
+; CHECK: %predphi = select <2 x i1> [[CMP]], <2 x i32> <i32 1, i32 1>, <2 x i32> %vec.ind
+
+; CHECK-LABEL: middle.block:
+; CHECK:          [[E1:%[a-zA-Z0-9.]+]] = extractelement <2 x i32> %predphi, i32 1
+
+; CHECK-LABEL: f1.exit.loopexit:
+; CHECK:          %.lcssa = phi i32 [ %tmp17, %bb16 ], [ [[E1]], %middle.block ]
+define i32 @test2()  {
+bb:
+  %b.promoted = load i32, i32* @b, align 4
+  br label %.lr.ph.i
+
+.lr.ph.i:
+  %tmp8 = phi i32 [ %tmp18, %bb16 ], [ %b.promoted, %bb ]
+  %tmp2 = icmp sgt i32 %tmp8, 10
+  br i1 %tmp2, label %bb16, label %bb10
+
+bb10:
+  br label %bb16
+
+bb16:
+  %tmp17 = phi i32 [ %tmp8, %bb10 ], [ 1, %.lr.ph.i ]
+  %tmp18 = add nsw i32 %tmp8, 1
+  %tmp19 = icmp slt i32 %tmp18, 4
+  br i1 %tmp19, label %.lr.ph.i, label %f1.exit.loopexit
+
+f1.exit.loopexit:
+  %.lcssa = phi i32 [ %tmp17, %bb16 ]
+  ret i32 %.lcssa
+}
+
+; more than 2 incoming values for tmp17 phi that is used outside loop.
+; CHECK-LABEL: test3(
+; CHECK-LABEL: vector.body:
+; CHECK:          %predphi = select <2 x i1> %{{.*}}, <2 x i32> <i32 1, i32 1>, <2 x i32> zeroinitializer
+; CHECK:          %predphi1 = select <2 x i1> %{{.*}}, <2 x i32> <i32 2, i32 2>, <2 x i32> %predphi
+
+; CHECK-LABEL: middle.block:
+; CHECK:          [[E1:%[a-zA-Z0-9.]+]] = extractelement <2 x i32> %predphi1, i32 1
+
+; CHECK-LABEL: f1.exit.loopexit:
+; CHECK:          phi i32 [ %tmp17, %bb16 ], [ [[E1]], %middle.block ]
+define i32 @test3(i32 %N)  {
+bb:
+  %b.promoted = load i32, i32* @b, align 4
+  br label %.lr.ph.i
+
+.lr.ph.i:
+  %tmp8 = phi i32 [ %tmp18, %bb16 ], [ %b.promoted, %bb ]
+  %tmp2 = icmp sgt i32 %tmp8, 10
+  br i1 %tmp2, label %bb16, label %bb10
+
+bb10:
+  %cmp = icmp sgt i32 %tmp8, %N
+  br i1  %cmp, label %bb12, label %bb16
+
+bb12:
+  br label %bb16
+
+bb16:
+  %tmp17 = phi i32 [ 0, %bb10 ], [ 1, %.lr.ph.i ], [ 2, %bb12 ]
+  %tmp18 = add nsw i32 %tmp8, 1
+  %tmp19 = icmp slt i32 %tmp18, 4
+  br i1 %tmp19, label %.lr.ph.i, label %f1.exit.loopexit
+
+f1.exit.loopexit:
+  %.lcssa = phi i32 [ %tmp17, %bb16 ]
+  ret i32 %.lcssa
+}
+
+; more than one incoming value for outside user: %.lcssa
+; CHECK-LABEL: test4(
+; CHECK-LABEL: vector.body:
+; CHECK:          %predphi = select <2 x i1>
+
+; CHECK-LABEL: middle.block:
+; CHECK:          [[E1:%[a-zA-Z0-9.]+]] = extractelement <2 x i32> %predphi, i32 1
+
+; CHECK-LABEL: f1.exit.loopexit.loopexit:
+; CHECK:          %tmp17.lcssa = phi i32 [ %tmp17, %bb16 ], [ [[E1]], %middle.block ]
+; CHECK-NEXT:     br label %f1.exit.loopexit
+
+; CHECK-LABEL: f1.exit.loopexit:
+; CHECK:          %.lcssa = phi i32 [ 2, %bb ], [ %tmp17.lcssa, %f1.exit.loopexit.loopexit ]
+define i32 @test4(i32 %N)  {
+bb:
+  %b.promoted = load i32, i32* @b, align 4
+  %icmp = icmp slt i32 %b.promoted, %N
+  br i1 %icmp, label %f1.exit.loopexit, label %.lr.ph.i
+
+.lr.ph.i:
+  %tmp8 = phi i32 [ %tmp18, %bb16 ], [ %b.promoted, %bb ]
+  %tmp2 = icmp sgt i32 %tmp8, 10
+  br i1 %tmp2, label %bb16, label %bb10
+
+bb10:
+  br label %bb16
+
+bb16:
+  %tmp17 = phi i32 [ 0, %bb10 ], [ 1, %.lr.ph.i ]
+  %tmp18 = add nsw i32 %tmp8, 1
+  %tmp19 = icmp slt i32 %tmp18, 4
+  br i1 %tmp19, label %.lr.ph.i, label %f1.exit.loopexit
+
+f1.exit.loopexit:
+  %.lcssa = phi i32 [ %tmp17, %bb16 ], [ 2, %bb ]
+  ret i32 %.lcssa
+}
+
+; non hdr phi that depends on reduction and is used outside the loop.
+; reduction phis are only allowed to have bump or reduction operations as the inside user, so we should
+; not vectorize this.
+; CHECK-LABEL: reduction_sum(
+; CHECK-NOT: <2 x i32>
+define i32 @reduction_sum(i32 %n, i32* noalias nocapture %A, i32* noalias nocapture %B) nounwind uwtable readonly noinline ssp {
+entry:
+  %c1 = icmp sgt i32 %n, 0
+  br i1 %c1, label %header, label %._crit_edge
+
+header:                                           ; preds = %0, %.lr.ph
+  %indvars.iv = phi i64 [ %indvars.iv.next, %bb16 ], [ 0, %entry ]
+  %sum.02 = phi i32 [ %c9, %bb16 ], [ 0, %entry ]
+  %c2 = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
+  %c3 = load i32, i32* %c2, align 4
+  %c4 = getelementptr inbounds i32, i32* %B, i64 %indvars.iv
+  %c5 = load i32, i32* %c4, align 4
+  %tmp2 = icmp sgt i32 %sum.02, 10
+  br i1 %tmp2, label %bb16, label %bb10
+
+bb10:
+  br label %bb16
+
+bb16:
+  %tmp17 = phi i32 [ %sum.02, %bb10 ], [ 1, %header ]
+  %c6 = trunc i64 %indvars.iv to i32
+  %c7 = add i32 %sum.02, %c6
+  %c8 = add i32 %c7, %c3
+  %c9 = add i32 %c8, %c5
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %._crit_edge, label %header
+
+._crit_edge:                                      ; preds = %.lr.ph, %0
+  %sum.0.lcssa = phi i32 [ 0, %entry ], [ %c9, %bb16 ]
+  %nonhdr.lcssa = phi i32 [ 1, %entry], [ %tmp17, %bb16 ]
+  ret i32 %sum.0.lcssa
+}
+
+; invalid cyclic dependency with header phi iv, which prevents iv from being
+; recognized as induction var.
+; cannot vectorize.
+; CHECK-LABEL: cyclic_dep_with_indvar(
+; CHECK-NOT: <2 x i32>
+define i32 @cyclic_dep_with_indvar()  {
+bb:
+  %b.promoted = load i32, i32* @b, align 4
+  br label %.lr.ph.i
+
+.lr.ph.i:
+  %iv = phi i32 [ %ivnext, %bb16 ], [ %b.promoted, %bb ]
+  %tmp2 = icmp sgt i32 %iv, 10
+  br i1 %tmp2, label %bb16, label %bb10
+
+bb10:
+  br label %bb16
+
+bb16:
+  %tmp17 = phi i32 [ 0, %bb10 ], [ %iv, %.lr.ph.i ]
+  %ivnext = add nsw i32 %tmp17, 1
+  %tmp19 = icmp slt i32 %ivnext, 4
+  br i1 %tmp19, label %.lr.ph.i, label %f1.exit.loopexit
+
+f1.exit.loopexit:
+  %.lcssa = phi i32 [ %tmp17, %bb16 ]
+  ret i32 %.lcssa
+}
+
+; non-reduction phi 'tmp17' used outside loop has cyclic dependence with %x.05 phi
+; cannot vectorize.
+; CHECK-LABEL: not_valid_reduction(
+; CHECK-NOT: <2 x i32>
+define i32 @not_valid_reduction(i32 %n, i32* noalias nocapture %A) nounwind uwtable readonly {
+entry:
+  %cmp4 = icmp sgt i32 %n, 0
+  br i1 %cmp4, label %for.body, label %for.end
+
+for.body:                                         ; preds = %entry, %for.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %latch ], [ 0, %entry ]
+  %x.05 = phi i32 [ %tmp17, %latch ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
+  %tmp0 = load i32, i32* %arrayidx, align 4
+  %tmp2 = icmp sgt i64 %indvars.iv, 10
+  %sub = sub nsw i32 %x.05, %tmp0
+  br i1 %tmp2, label %bb16, label %bb10
+
+bb10:
+  br label %bb16
+
+bb16:
+  %tmp17 = phi i32 [ 1, %bb10 ], [ %sub, %for.body ]
+  br label %latch
+
+latch:
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body, %entry
+  %x.0.lcssa = phi i32 [ 0, %entry ], [ %tmp17 , %latch ]
+  ret i32 %x.0.lcssa
+}