[llvm] r272715 - [LV] Enable vectorization of loops where the IV has an external use
Evgenii Stepanov via llvm-commits
llvm-commits at lists.llvm.org
Tue Jun 14 15:23:39 PDT 2016
This broke stuff.
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-autoconf/builds/21045
ninja clang && bin/clang++ -D_DEBUG
-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -Dcxx_EXPORTS
-I/code/llvm/projects/libcxx/include -m64 -O3 -DNDEBUG -fPIC
-UNDEBUG -std=c++11 -nostdinc++ -Wall -W -Wwrite-strings
-Wno-unused-parameter -Wno-long-long -Werror=return-type -Wno-error
-fPIC -c /code/llvm/projects/libcxx/src/locale.cpp
PHINode should have one entry for each predecessor of its parent basic block!
%incdec.ptr44326.lcssa = phi i32* [ %ind.escape, %middle.block380 ],
[ %incdec.ptr44326, %for.cond41.for.end47_crit_edge.loopexit ], [
%ind.end393, %middle.block380 ]
fatal error: error in backend: Broken function found, compilation aborted!
On Tue, Jun 14, 2016 at 2:27 PM, Michael Kuperstein via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: mkuper
> Date: Tue Jun 14 16:27:27 2016
> New Revision: 272715
>
> URL: http://llvm.org/viewvc/llvm-project?rev=272715&view=rev
> Log:
> [LV] Enable vectorization of loops where the IV has an external use
>
> Vectorizing loops with "escaping" IVs has been disabled since r190790, due to
> PR17179. This re-enables it, with support for external use of both
> "post-increment" (last iteration) and "pre-increment" (second-to-last iteration)
> IVs.
>
> Differential Revision: http://reviews.llvm.org/D21048
>
> Added:
> llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll
> Modified:
> llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
> llvm/trunk/test/Transforms/LoopVectorize/no_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=272715&r1=272714&r2=272715&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
> +++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Tue Jun 14 16:27:27 2016
> @@ -355,6 +355,12 @@ protected:
>
> /// Create an empty loop, based on the loop ranges of the old loop.
> void createEmptyLoop();
> +
> + /// Set up the values of the IVs correctly when exiting the vector loop.
> + void fixupIVUsers(PHINode *OrigPhi, const InductionDescriptor &II,
> + Value *CountRoundDown, Value *EndValue,
> + BasicBlock *MiddleBlock);
> +
> /// Create a new induction variable inside L.
> PHINode *createInductionVariable(Loop *L, Value *Start, Value *End,
> Value *Step, Instruction *DL);
> @@ -1433,13 +1439,11 @@ private:
> /// invariant.
> void collectStridedAccess(Value *LoadOrStoreInst);
>
> - /// \brief Returns true if we can vectorize using this PHI node as an
> - /// induction.
> - ///
> /// Updates the vectorization state by adding \p Phi to the inductions list.
> /// This can set \p Phi as the main induction of the loop if \p Phi is a
> /// better choice for the main induction than the existing one.
> - bool addInductionPhi(PHINode *Phi, InductionDescriptor ID);
> + void addInductionPhi(PHINode *Phi, InductionDescriptor ID,
> + SmallPtrSetImpl<Value *> &AllowedExit);
>
> /// Report an analysis message to assist the user in diagnosing loops that are
> /// not vectorized. These are handled as LoopAccessReport rather than
> @@ -1493,7 +1497,7 @@ private:
> /// Holds the widest induction type encountered.
> Type *WidestIndTy;
>
> - /// Allowed outside users. This holds the reduction
> + /// Allowed outside users. This holds the induction and reduction
> /// vars which can be accessed from outside the loop.
> SmallPtrSet<Value *, 4> AllowedExit;
> /// This set holds the variables which are known to be uniform after
> @@ -3219,6 +3223,9 @@ 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);
>
> @@ -3258,6 +3265,59 @@ void InnerLoopVectorizer::createEmptyLoo
> Hints.setAlreadyVectorized();
> }
>
> +// Fix up external users of the induction variable. At this point, we are
> +// in LCSSA form, with all external PHIs that use the IV having one input value,
> +// coming from the remainder loop. We need those PHIs to also have a correct
> +// value for the IV when arriving directly from the middle block.
> +void InnerLoopVectorizer::fixupIVUsers(PHINode *OrigPhi,
> + const InductionDescriptor &II,
> + Value *CountRoundDown, Value *EndValue,
> + BasicBlock *MiddleBlock) {
> + // There are two kinds of external IV usages - those that use the value
> + // computed in the last iteration (the PHI) and those that use the penultimate
> + // value (the value that feeds into the phi from the loop latch).
> + // We allow both, but they, obviously, have different values.
> +
> + // We only expect at most one of each kind of user. This is because LCSSA will
> + // canonicalize the users to a single PHI node per exit block, and we
> + // currently only vectorize loops with a single exit.
> + assert(OrigLoop->getExitBlock() && "Expected a single exit block");
> +
> + // An external user of the last iteration's value should see the value that
> + // the remainder loop uses to initialize its own IV.
> + Value *PostInc = OrigPhi->getIncomingValueForBlock(OrigLoop->getLoopLatch());
> + for (User *U : PostInc->users()) {
> + Instruction *UI = cast<Instruction>(U);
> + if (!OrigLoop->contains(UI)) {
> + assert(isa<PHINode>(UI) && "Expected LCSSA form");
> + cast<PHINode>(UI)->addIncoming(EndValue, MiddleBlock);
> + break;
> + }
> + }
> +
> + // An external user of the penultimate value need to see EndValue - Step.
> + // The simplest way to get this is to recompute it from the constituent SCEVs,
> + // that is Start + (Step * (CRD - 1)).
> + for (User *U : OrigPhi->users()) {
> + Instruction *UI = cast<Instruction>(U);
> + if (!OrigLoop->contains(UI)) {
> + assert(isa<PHINode>(UI) && "Expected LCSSA form");
> + const DataLayout &DL =
> + OrigLoop->getHeader()->getModule()->getDataLayout();
> +
> + IRBuilder<> B(MiddleBlock->getTerminator());
> + Value *CountMinusOne = B.CreateSub(
> + CountRoundDown, ConstantInt::get(CountRoundDown->getType(), 1));
> + Value *CMO = B.CreateSExtOrTrunc(CountMinusOne, II.getStep()->getType(),
> + "cast.cmo");
> + Value *Escape = II.transform(B, CMO, PSE.getSE(), DL);
> + Escape->setName("ind.escape");
> + cast<PHINode>(UI)->addIncoming(Escape, MiddleBlock);
> + break;
> + }
> + }
> +}
> +
> namespace {
> struct CSEDenseMapInfo {
> static bool canHandle(Instruction *I) {
> @@ -4639,10 +4699,10 @@ static Type *getWiderType(const DataLayo
> /// \brief Check that the instruction has outside loop users and is not an
> /// identified reduction variable.
> static bool hasOutsideLoopUser(const Loop *TheLoop, Instruction *Inst,
> - SmallPtrSetImpl<Value *> &Reductions) {
> - // Reduction instructions are allowed to have exit users. All other
> - // instructions must not have external users.
> - if (!Reductions.count(Inst))
> + SmallPtrSetImpl<Value *> &AllowedExit) {
> + // Reduction and Induction instructions are allowed to have exit users. All
> + // other instructions must not have external users.
> + if (!AllowedExit.count(Inst))
> // Check that all of the users of the loop are inside the BB.
> for (User *U : Inst->users()) {
> Instruction *UI = cast<Instruction>(U);
> @@ -4655,8 +4715,9 @@ static bool hasOutsideLoopUser(const Loo
> return false;
> }
>
> -bool LoopVectorizationLegality::addInductionPhi(PHINode *Phi,
> - InductionDescriptor ID) {
> +void LoopVectorizationLegality::addInductionPhi(
> + PHINode *Phi, InductionDescriptor ID,
> + SmallPtrSetImpl<Value *> &AllowedExit) {
> Inductions[Phi] = ID;
> Type *PhiTy = Phi->getType();
> const DataLayout &DL = Phi->getModule()->getDataLayout();
> @@ -4682,18 +4743,13 @@ bool LoopVectorizationLegality::addInduc
> Induction = Phi;
> }
>
> - DEBUG(dbgs() << "LV: Found an induction variable.\n");
> + // Both the PHI node itself, and the "post-increment" value feeding
> + // back into the PHI node may have external users.
> + AllowedExit.insert(Phi);
> + AllowedExit.insert(Phi->getIncomingValueForBlock(TheLoop->getLoopLatch()));
>
> - // Until we explicitly handle the case of an induction variable with
> - // an outside loop user we have to give up vectorizing this loop.
> - if (hasOutsideLoopUser(TheLoop, Phi, AllowedExit)) {
> - emitAnalysis(VectorizationReport(Phi) <<
> - "use of induction value outside of the "
> - "loop is not handled by vectorizer");
> - return false;
> - }
> -
> - return true;
> + DEBUG(dbgs() << "LV: Found an induction variable.\n");
> + return;
> }
>
> bool LoopVectorizationLegality::canVectorizeInstrs() {
> @@ -4757,8 +4813,7 @@ bool LoopVectorizationLegality::canVecto
>
> InductionDescriptor ID;
> if (InductionDescriptor::isInductionPHI(Phi, PSE, ID)) {
> - if (!addInductionPhi(Phi, ID))
> - return false;
> + addInductionPhi(Phi, ID, AllowedExit);
> continue;
> }
>
> @@ -4770,8 +4825,7 @@ bool LoopVectorizationLegality::canVecto
> // As a last resort, coerce the PHI to a AddRec expression
> // and re-try classifying it a an induction PHI.
> if (InductionDescriptor::isInductionPHI(Phi, PSE, ID, true)) {
> - if (!addInductionPhi(Phi, ID))
> - return false;
> + addInductionPhi(Phi, ID, AllowedExit);
> continue;
> }
>
>
> Added: 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=272715&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll (added)
> +++ llvm/trunk/test/Transforms/LoopVectorize/iv_outside_user.ll Tue Jun 14 16:27:27 2016
> @@ -0,0 +1,84 @@
> +; RUN: opt -S -loop-vectorize -force-vector-interleave=1 -force-vector-width=2 < %s | FileCheck %s
> +
> +; CHECK-LABEL: @postinc
> +; CHECK-LABEL: scalar.ph:
> +; CHECK: %bc.resume.val = phi i32 [ %n.vec, %middle.block ], [ 0, %entry ]
> +; CHECK-LABEL: for.end:
> +; CHECK: %[[RET:.*]] = phi i32 [ {{.*}}, %for.body ], [ %n.vec, %middle.block ]
> +; CHECK: ret i32 %[[RET]]
> +define i32 @postinc(i32 %k) {
> +entry:
> + br label %for.body
> +
> +for.body:
> + %inc.phi = phi i32 [ 0, %entry ], [ %inc, %for.body ]
> + %inc = add nsw i32 %inc.phi, 1
> + %cmp = icmp eq i32 %inc, %k
> + br i1 %cmp, label %for.end, label %for.body
> +
> +for.end:
> + ret i32 %inc
> +}
> +
> +; CHECK-LABEL: @preinc
> +; CHECK-LABEL: middle.block:
> +; CHECK: %3 = sub i32 %n.vec, 1
> +; CHECK: %ind.escape = add i32 0, %3
> +; CHECK-LABEL: scalar.ph:
> +; CHECK: %bc.resume.val = phi i32 [ %n.vec, %middle.block ], [ 0, %entry ]
> +; CHECK-LABEL: for.end:
> +; CHECK: %[[RET:.*]] = phi i32 [ {{.*}}, %for.body ], [ %ind.escape, %middle.block ]
> +; CHECK: ret i32 %[[RET]]
> +define i32 @preinc(i32 %k) {
> +entry:
> + br label %for.body
> +
> +for.body:
> + %inc.phi = phi i32 [ 0, %entry ], [ %inc, %for.body ]
> + %inc = add nsw i32 %inc.phi, 1
> + %cmp = icmp eq i32 %inc, %k
> + br i1 %cmp, label %for.end, label %for.body
> +
> +for.end:
> + ret i32 %inc.phi
> +}
> +
> +; CHECK-LABEL: @constpre
> +; CHECK-LABEL: for.end:
> +; CHECK: %[[RET:.*]] = phi i32 [ {{.*}}, %for.body ], [ 2, %middle.block ]
> +; CHECK: ret i32 %[[RET]]
> +define i32 @constpre() {
> +entry:
> + br label %for.body
> +
> +for.body:
> + %inc.phi = phi i32 [ 32, %entry ], [ %inc, %for.body ]
> + %inc = sub nsw i32 %inc.phi, 2
> + %cmp = icmp eq i32 %inc, 0
> + br i1 %cmp, label %for.end, label %for.body
> +
> +for.end:
> + ret i32 %inc.phi
> +}
> +
> +; CHECK-LABEL: @geppre
> +; CHECK-LABEL: middle.block:
> +; CHECK: %ind.escape = getelementptr i32, i32* %ptr, i64 124
> +; CHECK-LABEL: for.end:
> +; CHECK: %[[RET:.*]] = phi i32* [ {{.*}}, %for.body ], [ %ind.escape, %middle.block ]
> +; CHECK: ret i32* %[[RET]]
> +define i32* @geppre(i32* %ptr) {
> +entry:
> + br label %for.body
> +
> +for.body:
> + %inc.phi = phi i32 [ 0, %entry ], [ %inc, %for.body ]
> + %ptr.phi = phi i32* [ %ptr, %entry ], [ %inc.ptr, %for.body ]
> + %inc = add nsw i32 %inc.phi, 1
> + %inc.ptr = getelementptr i32, i32* %ptr.phi, i32 4
> + %cmp = icmp eq i32 %inc, 32
> + br i1 %cmp, label %for.end, label %for.body
> +
> +for.end:
> + ret i32* %ptr.phi
> +}
>
> Modified: llvm/trunk/test/Transforms/LoopVectorize/no_outside_user.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/no_outside_user.ll?rev=272715&r1=272714&r2=272715&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopVectorize/no_outside_user.ll (original)
> +++ llvm/trunk/test/Transforms/LoopVectorize/no_outside_user.ll Tue Jun 14 16:27:27 2016
> @@ -1,7 +1,6 @@
> ; 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
> -; CHECK: remark: {{.*}}: loop not vectorized: use of induction value outside of the loop is not handled by vectorizer
>
> 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"
>
> @@ -41,34 +40,3 @@ f1.exit.loopexit:
> %.lcssa = phi i32 [ %tmp17, %bb16 ]
> ret i32 %.lcssa
> }
> -
> -; Don't vectorize this loop. Its phi node (induction variable) has an outside
> -; loop user. We currently don't handle this case.
> -; PR17179
> -
> -; CHECK-LABEL: @test2(
> -; CHECK-NOT: <2 x
> -
> - at x1 = common global i32 0, align 4
> - at x2 = common global i32 0, align 4
> - at x0 = common global i32 0, align 4
> -
> -define i32 @test2() {
> -entry:
> - store i32 0, i32* @x1, align 4
> - %0 = load i32, i32* @x0, align 4
> - br label %for.cond1.preheader
> -
> -for.cond1.preheader:
> - %inc7 = phi i32 [ 0, %entry ], [ %inc, %for.cond1.preheader ]
> - %inc = add nsw i32 %inc7, 1
> - %cmp = icmp eq i32 %inc, 52
> - br i1 %cmp, label %for.end5, label %for.cond1.preheader
> -
> -for.end5:
> - %inc7.lcssa = phi i32 [ %inc7, %for.cond1.preheader ]
> - %xor = xor i32 %inc7.lcssa, %0
> - store i32 52, i32* @x1, align 4
> - store i32 1, i32* @x2, align 4
> - ret i32 %xor
> -}
>
>
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