From: Devang Patel Date: Thu, 14 Aug 2008 20:58:31 +0000 (+0000) Subject: If IV is used in a int-to-float cast inside the loop then try to eliminate the cast... X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=79ceb4463efc699c8aa1647d4ecbc15bed19e1c9;p=oota-llvm.git If IV is used in a int-to-float cast inside the loop then try to eliminate the cast opeation. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@54786 91177308-0d34-0410-b5e6-96231b3b80d8 --- diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp index 04faa0aa508..37a93e114a0 100644 --- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp +++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp @@ -45,6 +45,7 @@ STATISTIC(NumReduced , "Number of GEPs strength reduced"); STATISTIC(NumInserted, "Number of PHIs inserted"); STATISTIC(NumVariable, "Number of PHIs with variable strides"); STATISTIC(NumEliminated , "Number of strides eliminated"); +STATISTIC(NumShadow , "Number of Shdow IVs optimized"); namespace { @@ -177,6 +178,10 @@ private: IVStrideUse* &CondUse, const SCEVHandle* &CondStride); void OptimizeIndvars(Loop *L); + + /// OptimizeShadowIV - If IV is used in a int-to-float cast + /// inside the loop then try to eliminate the cast opeation. + void OptimizeShadowIV(Loop *L); bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse, const SCEVHandle *&CondStride); bool RequiresTypeConversion(const Type *Ty, const Type *NewTy); @@ -1689,12 +1694,108 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond, return Cond; } +/// OptimizeShadowIV - If IV is used in a int-to-float cast +/// inside the loop then try to eliminate the cast opeation. +void LoopStrengthReduce::OptimizeShadowIV(Loop *L) { + + for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e; + ++Stride) { + std::map::iterator SI = + IVUsesByStride.find(StrideOrder[Stride]); + assert(SI != IVUsesByStride.end() && "Stride doesn't exist!"); + + for (std::vector::iterator UI = SI->second.Users.begin(), + E = SI->second.Users.end(); UI != E; /* empty */) { + std::vector::iterator CandidateUI = UI; + UI++; + Instruction *ShadowUse = CandidateUI->User; + const Type *DestTy = NULL; + + /* If shadow use is a int->float cast then insert a second IV + to elminate this cast. + + for (unsigned i = 0; i < n; ++i) + foo((double)i); + + is trnasformed into + + double d = 0.0; + for (unsigned i = 0; i < n; ++i, ++d) + foo(d); + */ + UIToFPInst *UCast = dyn_cast(CandidateUI->User); + if (UCast) + DestTy = UCast->getDestTy(); + else { + SIToFPInst *SCast = dyn_cast(CandidateUI->User); + if (!SCast) continue; + DestTy = SCast->getDestTy(); + } + + PHINode *PH = dyn_cast(ShadowUse->getOperand(0)); + if (!PH) continue; + if (PH->getNumIncomingValues() != 2) continue; + + unsigned Entry, Latch; + if (PH->getIncomingBlock(0) == L->getLoopPreheader()) { + Entry = 0; + Latch = 1; + } else { + Entry = 1; + Latch = 0; + } + + ConstantInt *Init = dyn_cast(PH->getIncomingValue(Entry)); + if (!Init) continue; + ConstantFP *NewInit = ConstantFP::get(DestTy, Init->getZExtValue()); + + BinaryOperator *Incr = + dyn_cast(PH->getIncomingValue(Latch)); + if (!Incr) continue; + if (Incr->getOpcode() != Instruction::Add + && Incr->getOpcode() != Instruction::Sub) + continue; + + /* Initialize new IV, double d = 0.0 in above example. */ + ConstantInt *C = NULL; + if (Incr->getOperand(0) == PH) + C = dyn_cast(Incr->getOperand(1)); + else if (Incr->getOperand(1) == PH) + C = dyn_cast(Incr->getOperand(0)); + else + continue; + + if (!C) continue; + + /* create new icnrement. '++d' in above example. */ + ConstantFP *CFP = ConstantFP::get(DestTy, C->getZExtValue()); + BinaryOperator *NewIncr = + BinaryOperator::Create(Incr->getOpcode(), + NewInit, CFP, "IV.S.next.", Incr); + + /* Add new PHINode. */ + PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH); + NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry)); + NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch)); + + /* Remove cast operation */ + ShadowUse->replaceAllUsesWith(NewPH); + ShadowUse->eraseFromParent(); + SI->second.Users.erase(CandidateUI); + NumShadow++; + break; + } + } +} + // OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar // uses in the loop, look to see if we can eliminate some, in favor of using // common indvars for the different uses. void LoopStrengthReduce::OptimizeIndvars(Loop *L) { // TODO: implement optzns here. + OptimizeShadowIV(L); + // Finally, get the terminating condition for the loop if possible. If we // can, we want to change it to use a post-incremented version of its // induction variable, to allow coalescing the live ranges for the IV into diff --git a/test/Transforms/LoopStrengthReduce/2008-08-14-ShadowIV.ll b/test/Transforms/LoopStrengthReduce/2008-08-14-ShadowIV.ll new file mode 100644 index 00000000000..681c9be1675 --- /dev/null +++ b/test/Transforms/LoopStrengthReduce/2008-08-14-ShadowIV.ll @@ -0,0 +1,27 @@ +; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis | grep "phi double" + +define void @foobar(i32 %n) nounwind { +entry: + icmp eq i32 %n, 0 ; :0 [#uses=2] + br i1 %0, label %return, label %bb.nph + +bb.nph: ; preds = %entry + %umax = select i1 %0, i32 1, i32 %n ; [#uses=1] + br label %bb + +bb: ; preds = %bb, %bb.nph + %i.03 = phi i32 [ 0, %bb.nph ], [ %indvar.next, %bb ] ; [#uses=3] + tail call void @bar( i32 %i.03 ) nounwind + uitofp i32 %i.03 to double ; :1 [#uses=1] + tail call void @foo( double %1 ) nounwind + %indvar.next = add i32 %i.03, 1 ; [#uses=2] + %exitcond = icmp eq i32 %indvar.next, %umax ; [#uses=1] + br i1 %exitcond, label %return, label %bb + +return: ; preds = %bb, %entry + ret void +} + +declare void @bar(i32) + +declare void @foo(double)