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Add diagnostics to the vectorizer cost model.
When the cost model determines vectorization is not possible/profitable these remarks print an analysis of that decision. Note that in selectVectorizationFactor() we can assume that OptForSize and ForceVectorization are mutually exclusive. Reviewed by Arnold Schwaighofer git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214599 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -209,6 +209,7 @@ namespace {
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// Forward declarations.
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class LoopVectorizationLegality;
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class LoopVectorizationCostModel;
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class LoopVectorizeHints;
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/// Optimization analysis message produced during vectorization. Messages inform
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/// the user why vectorization did not occur.
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@ -877,8 +878,9 @@ public:
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LoopVectorizationCostModel(Loop *L, ScalarEvolution *SE, LoopInfo *LI,
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LoopVectorizationLegality *Legal,
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const TargetTransformInfo &TTI,
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const DataLayout *DL, const TargetLibraryInfo *TLI)
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: TheLoop(L), SE(SE), LI(LI), Legal(Legal), TTI(TTI), DL(DL), TLI(TLI) {}
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const DataLayout *DL, const TargetLibraryInfo *TLI,
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const Function *F, const LoopVectorizeHints *Hints)
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: TheLoop(L), SE(SE), LI(LI), Legal(Legal), TTI(TTI), DL(DL), TLI(TLI), TheFunction(F), Hints(Hints) {}
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/// Information about vectorization costs
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struct VectorizationFactor {
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@ -889,9 +891,7 @@ public:
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/// This method checks every power of two up to VF. If UserVF is not ZERO
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/// then this vectorization factor will be selected if vectorization is
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/// possible.
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VectorizationFactor selectVectorizationFactor(bool OptForSize,
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unsigned UserVF,
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bool ForceVectorization);
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VectorizationFactor selectVectorizationFactor(bool OptForSize);
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/// \return The size (in bits) of the widest type in the code that
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/// needs to be vectorized. We ignore values that remain scalar such as
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@ -903,8 +903,7 @@ public:
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/// based on register pressure and other parameters.
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/// VF and LoopCost are the selected vectorization factor and the cost of the
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/// selected VF.
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unsigned selectUnrollFactor(bool OptForSize, unsigned UserUF, unsigned VF,
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unsigned LoopCost);
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unsigned selectUnrollFactor(bool OptForSize, unsigned VF, unsigned LoopCost);
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/// \brief A struct that represents some properties of the register usage
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/// of a loop.
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@ -940,6 +939,16 @@ private:
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/// as a vector operation.
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bool isConsecutiveLoadOrStore(Instruction *I);
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/// Report an analysis message to assist the user in diagnosing loops that are
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/// not vectorized.
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void emitAnalysis(Report &Message) {
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DebugLoc DL = TheLoop->getStartLoc();
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if (Instruction *I = Message.getInstr())
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DL = I->getDebugLoc();
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emitOptimizationRemarkAnalysis(TheFunction->getContext(), DEBUG_TYPE,
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*TheFunction, DL, Message.str());
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}
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/// The loop that we evaluate.
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Loop *TheLoop;
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/// Scev analysis.
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@ -954,6 +963,9 @@ private:
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const DataLayout *DL;
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/// Target Library Info.
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const TargetLibraryInfo *TLI;
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const Function *TheFunction;
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// Loop Vectorize Hint.
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const LoopVectorizeHints *Hints;
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};
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/// Utility class for getting and setting loop vectorizer hints in the form
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@ -1301,7 +1313,7 @@ struct LoopVectorize : public FunctionPass {
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}
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// Use the cost model.
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LoopVectorizationCostModel CM(L, SE, LI, &LVL, *TTI, DL, TLI);
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LoopVectorizationCostModel CM(L, SE, LI, &LVL, *TTI, DL, TLI, F, &Hints);
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// Check the function attributes to find out if this function should be
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// optimized for size.
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@ -1336,13 +1348,11 @@ struct LoopVectorize : public FunctionPass {
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// Select the optimal vectorization factor.
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const LoopVectorizationCostModel::VectorizationFactor VF =
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CM.selectVectorizationFactor(OptForSize, Hints.getWidth(),
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Hints.getForce() ==
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LoopVectorizeHints::FK_Enabled);
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CM.selectVectorizationFactor(OptForSize);
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// Select the unroll factor.
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const unsigned UF =
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CM.selectUnrollFactor(OptForSize, Hints.getUnroll(), VF.Width, VF.Cost);
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CM.selectUnrollFactor(OptForSize, VF.Width, VF.Cost);
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DEBUG(dbgs() << "LV: Found a vectorizable loop (" << VF.Width << ") in "
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<< DebugLocStr << '\n');
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@ -5263,17 +5273,17 @@ bool LoopVectorizationLegality::blockCanBePredicated(BasicBlock *BB,
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}
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LoopVectorizationCostModel::VectorizationFactor
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LoopVectorizationCostModel::selectVectorizationFactor(bool OptForSize,
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unsigned UserVF,
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bool ForceVectorization) {
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LoopVectorizationCostModel::selectVectorizationFactor(bool OptForSize) {
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// Width 1 means no vectorize
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VectorizationFactor Factor = { 1U, 0U };
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if (OptForSize && Legal->getRuntimePointerCheck()->Need) {
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emitAnalysis(Report() << "runtime pointer checks needed. Enable vectorization of this loop with '#pragma clang loop vectorize(enable)' when compiling with -Os");
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DEBUG(dbgs() << "LV: Aborting. Runtime ptr check is required in Os.\n");
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return Factor;
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}
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if (!EnableCondStoresVectorization && Legal->NumPredStores) {
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emitAnalysis(Report() << "store that is conditionally executed prevents vectorization");
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DEBUG(dbgs() << "LV: No vectorization. There are conditional stores.\n");
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return Factor;
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}
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@ -5308,6 +5318,7 @@ LoopVectorizationCostModel::selectVectorizationFactor(bool OptForSize,
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if (OptForSize) {
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// If we are unable to calculate the trip count then don't try to vectorize.
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if (TC < 2) {
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emitAnalysis(Report() << "unable to calculate the loop count due to complex control flow");
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DEBUG(dbgs() << "LV: Aborting. A tail loop is required in Os.\n");
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return Factor;
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}
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@ -5321,11 +5332,13 @@ LoopVectorizationCostModel::selectVectorizationFactor(bool OptForSize,
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// If the trip count that we found modulo the vectorization factor is not
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// zero then we require a tail.
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if (VF < 2) {
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emitAnalysis(Report() << "cannot optimize for size and vectorize at the same time. Enable vectorization of this loop with '#pragma clang loop vectorize(enable)' when compiling with -Os");
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DEBUG(dbgs() << "LV: Aborting. A tail loop is required in Os.\n");
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return Factor;
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}
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}
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int UserVF = Hints->getWidth();
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if (UserVF != 0) {
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assert(isPowerOf2_32(UserVF) && "VF needs to be a power of two");
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DEBUG(dbgs() << "LV: Using user VF " << UserVF << ".\n");
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@ -5341,6 +5354,7 @@ LoopVectorizationCostModel::selectVectorizationFactor(bool OptForSize,
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unsigned Width = 1;
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DEBUG(dbgs() << "LV: Scalar loop costs: " << (int)ScalarCost << ".\n");
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bool ForceVectorization = Hints->getForce() == LoopVectorizeHints::FK_Enabled;
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// Ignore scalar width, because the user explicitly wants vectorization.
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if (ForceVectorization && VF > 1) {
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Width = 2;
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@ -5410,7 +5424,6 @@ unsigned LoopVectorizationCostModel::getWidestType() {
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unsigned
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LoopVectorizationCostModel::selectUnrollFactor(bool OptForSize,
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unsigned UserUF,
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unsigned VF,
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unsigned LoopCost) {
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@ -5429,6 +5442,7 @@ LoopVectorizationCostModel::selectUnrollFactor(bool OptForSize,
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// to the increased register pressure.
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// Use the user preference, unless 'auto' is selected.
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int UserUF = Hints->getUnroll();
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if (UserUF != 0)
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return UserUF;
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58
test/Transforms/LoopVectorize/conditional-assignment.ll
Normal file
58
test/Transforms/LoopVectorize/conditional-assignment.ll
Normal file
@ -0,0 +1,58 @@
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; RUN: opt < %s -loop-vectorize -S -pass-remarks-missed='loop-vectorize' -pass-remarks-analysis='loop-vectorize' 2>&1 | FileCheck %s
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; CHECK: remark: source.c:2:8: loop not vectorized: store that is conditionally executed prevents vectorization
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target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-apple-macosx10.9.0"
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; Function Attrs: nounwind ssp uwtable
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define void @conditional_store(i32* noalias nocapture %indices) #0 {
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entry:
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br label %for.body, !dbg !10
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for.body: ; preds = %for.inc, %entry
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%indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.inc ]
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%arrayidx = getelementptr inbounds i32* %indices, i64 %indvars.iv, !dbg !12
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%0 = load i32* %arrayidx, align 4, !dbg !12, !tbaa !14
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%cmp1 = icmp eq i32 %0, 1024, !dbg !12
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br i1 %cmp1, label %if.then, label %for.inc, !dbg !12
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if.then: ; preds = %for.body
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store i32 0, i32* %arrayidx, align 4, !dbg !18, !tbaa !14
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br label %for.inc, !dbg !18
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for.inc: ; preds = %for.body, %if.then
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !10
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%exitcond = icmp eq i64 %indvars.iv.next, 4096, !dbg !10
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br i1 %exitcond, label %for.end, label %for.body, !dbg !10
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for.end: ; preds = %for.inc
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ret void, !dbg !19
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}
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attributes #0 = { nounwind }
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!7, !8}
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!llvm.ident = !{!9}
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!1 = metadata !{metadata !"source.c", metadata !"."}
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!2 = metadata !{}
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!3 = metadata !{metadata !4}
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