From 1f96e67f78110d0ac5b30a32375097a28f869c63 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Thu, 17 Sep 2009 18:05:20 +0000 Subject: [PATCH] Teach ScalarEvolution how to reason about no-wrap flags on loops where the induction variable has a non-unit stride, such as {0,+,2}, and there are expressions such as {1,+,2} inside the loop formed with or or add nsw operators. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82151 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/Analysis/ScalarEvolution.h | 3 +- lib/Analysis/ScalarEvolution.cpp | 52 ++++++++++---- test/Analysis/ScalarEvolution/nsw-offset.ll | 76 +++++++++++++++++++++ 3 files changed, 115 insertions(+), 16 deletions(-) create mode 100644 test/Analysis/ScalarEvolution/nsw-offset.ll diff --git a/include/llvm/Analysis/ScalarEvolution.h b/include/llvm/Analysis/ScalarEvolution.h index e3be8ee7f30..548f8f6ad7d 100644 --- a/include/llvm/Analysis/ScalarEvolution.h +++ b/include/llvm/Analysis/ScalarEvolution.h @@ -253,7 +253,8 @@ namespace llvm { /// CouldNotCompute if an intermediate computation overflows. const SCEV *getBECount(const SCEV *Start, const SCEV *End, - const SCEV *Step); + const SCEV *Step, + bool NoWrap); /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given /// loop, lazily computing new values if the loop hasn't been analyzed diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index 64663863b25..fa452358c8d 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -2972,8 +2972,20 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) { const SCEV *LHS = getSCEV(U->getOperand(0)); const APInt &CIVal = CI->getValue(); if (GetMinTrailingZeros(LHS) >= - (CIVal.getBitWidth() - CIVal.countLeadingZeros())) - return getAddExpr(LHS, getSCEV(U->getOperand(1))); + (CIVal.getBitWidth() - CIVal.countLeadingZeros())) { + // Build a plain add SCEV. + const SCEV *S = getAddExpr(LHS, getSCEV(CI)); + // If the LHS of the add was an addrec and it has no-wrap flags, + // transfer the no-wrap flags, since an or won't introduce a wrap. + if (const SCEVAddRecExpr *NewAR = dyn_cast(S)) { + const SCEVAddRecExpr *OldAR = cast(LHS); + if (OldAR->hasNoUnsignedWrap()) + const_cast(NewAR)->setHasNoUnsignedWrap(true); + if (OldAR->hasNoSignedWrap()) + const_cast(NewAR)->setHasNoSignedWrap(true); + } + return S; + } } break; case Instruction::Xor: @@ -4795,7 +4807,8 @@ ScalarEvolution::isImpliedCondOperandsHelper(ICmpInst::Predicate Pred, /// CouldNotCompute if an intermediate computation overflows. const SCEV *ScalarEvolution::getBECount(const SCEV *Start, const SCEV *End, - const SCEV *Step) { + const SCEV *Step, + bool NoWrap) { const Type *Ty = Start->getType(); const SCEV *NegOne = getIntegerSCEV(-1, Ty); const SCEV *Diff = getMinusSCEV(End, Start); @@ -4805,15 +4818,17 @@ const SCEV *ScalarEvolution::getBECount(const SCEV *Start, // the division will effectively round up. const SCEV *Add = getAddExpr(Diff, RoundUp); - // Check Add for unsigned overflow. - // TODO: More sophisticated things could be done here. - const Type *WideTy = IntegerType::get(getContext(), - getTypeSizeInBits(Ty) + 1); - const SCEV *EDiff = getZeroExtendExpr(Diff, WideTy); - const SCEV *ERoundUp = getZeroExtendExpr(RoundUp, WideTy); - const SCEV *OperandExtendedAdd = getAddExpr(EDiff, ERoundUp); - if (getZeroExtendExpr(Add, WideTy) != OperandExtendedAdd) - return getCouldNotCompute(); + if (!NoWrap) { + // Check Add for unsigned overflow. + // TODO: More sophisticated things could be done here. + const Type *WideTy = IntegerType::get(getContext(), + getTypeSizeInBits(Ty) + 1); + const SCEV *EDiff = getZeroExtendExpr(Diff, WideTy); + const SCEV *ERoundUp = getZeroExtendExpr(RoundUp, WideTy); + const SCEV *OperandExtendedAdd = getAddExpr(EDiff, ERoundUp); + if (getZeroExtendExpr(Add, WideTy) != OperandExtendedAdd) + return getCouldNotCompute(); + } return getUDivExpr(Add, Step); } @@ -4831,6 +4846,10 @@ ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS, if (!AddRec || AddRec->getLoop() != L) return getCouldNotCompute(); + // Check to see if we have a flag which makes analysis easy. + bool NoWrap = isSigned ? AddRec->hasNoSignedWrap() : + AddRec->hasNoUnsignedWrap(); + if (AddRec->isAffine()) { // FORNOW: We only support unit strides. unsigned BitWidth = getTypeSizeInBits(AddRec->getType()); @@ -4843,7 +4862,10 @@ ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS, if (CStep->isOne()) { // With unit stride, the iteration never steps past the limit value. } else if (CStep->getValue()->getValue().isStrictlyPositive()) { - if (const SCEVConstant *CLimit = dyn_cast(RHS)) { + if (NoWrap) { + // We know the iteration won't step past the maximum value for its type. + ; + } else if (const SCEVConstant *CLimit = dyn_cast(RHS)) { // Test whether a positive iteration iteration can step past the limit // value and past the maximum value for its type in a single step. if (isSigned) { @@ -4896,11 +4918,11 @@ ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS, // Finally, we subtract these two values and divide, rounding up, to get // the number of times the backedge is executed. - const SCEV *BECount = getBECount(Start, End, Step); + const SCEV *BECount = getBECount(Start, End, Step, NoWrap); // The maximum backedge count is similar, except using the minimum start // value and the maximum end value. - const SCEV *MaxBECount = getBECount(MinStart, MaxEnd, Step); + const SCEV *MaxBECount = getBECount(MinStart, MaxEnd, Step, NoWrap); return BackedgeTakenInfo(BECount, MaxBECount); } diff --git a/test/Analysis/ScalarEvolution/nsw-offset.ll b/test/Analysis/ScalarEvolution/nsw-offset.ll new file mode 100644 index 00000000000..1e165bf6222 --- /dev/null +++ b/test/Analysis/ScalarEvolution/nsw-offset.ll @@ -0,0 +1,76 @@ +; RUN: opt < %s -S -analyze -scalar-evolution -disable-output | FileCheck %s + +; ScalarEvolution should be able to fold away the sign-extensions +; on this loop with a primary induction variable incremented with +; a nsw add of 2. + +target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128" + +define void @foo(i32 %n, double* nocapture %d, double* nocapture %q) nounwind { +entry: + %0 = icmp sgt i32 %n, 0 ; [#uses=1] + br i1 %0, label %bb.nph, label %return + +bb.nph: ; preds = %entry + br label %bb + +bb: ; preds = %bb.nph, %bb1 + %i.01 = phi i32 [ %16, %bb1 ], [ 0, %bb.nph ] ; [#uses=5] + +; CHECK: %1 = sext i32 %i.01 to i64 +; CHECK: --> {0,+,2} + %1 = sext i32 %i.01 to i64 ; [#uses=1] + +; CHECK: %2 = getelementptr inbounds double* %d, i64 %1 +; CHECK: --> {%d,+,16} + %2 = getelementptr inbounds double* %d, i64 %1 ; [#uses=1] + + %3 = load double* %2, align 8 ; [#uses=1] + %4 = sext i32 %i.01 to i64 ; [#uses=1] + %5 = getelementptr inbounds double* %q, i64 %4 ; [#uses=1] + %6 = load double* %5, align 8 ; [#uses=1] + %7 = or i32 %i.01, 1 ; [#uses=1] + +; CHECK: %8 = sext i32 %7 to i64 +; CHECK: --> {1,+,2} + %8 = sext i32 %7 to i64 ; [#uses=1] + +; CHECK: %9 = getelementptr inbounds double* %q, i64 %8 +; CHECK: {(8 + %q),+,16} + %9 = getelementptr inbounds double* %q, i64 %8 ; [#uses=1] + +; Artificially repeat the above three instructions, this time using +; add nsw instead of or. + %t7 = add nsw i32 %i.01, 1 ; [#uses=1] + +; CHECK: %t8 = sext i32 %t7 to i64 +; CHECK: --> {1,+,2} + %t8 = sext i32 %t7 to i64 ; [#uses=1] + +; CHECK: %t9 = getelementptr inbounds double* %q, i64 %t8 +; CHECK: {(8 + %q),+,16} + %t9 = getelementptr inbounds double* %q, i64 %t8 ; [#uses=1] + + %10 = load double* %9, align 8 ; [#uses=1] + %11 = fadd double %6, %10 ; [#uses=1] + %12 = fadd double %11, 3.200000e+00 ; [#uses=1] + %13 = fmul double %3, %12 ; [#uses=1] + %14 = sext i32 %i.01 to i64 ; [#uses=1] + %15 = getelementptr inbounds double* %d, i64 %14 ; [#uses=1] + store double %13, double* %15, align 8 + %16 = add nsw i32 %i.01, 2 ; [#uses=2] + br label %bb1 + +bb1: ; preds = %bb + %17 = icmp slt i32 %16, %n ; [#uses=1] + br i1 %17, label %bb, label %bb1.return_crit_edge + +bb1.return_crit_edge: ; preds = %bb1 + br label %return + +return: ; preds = %bb1.return_crit_edge, %entry + ret void +} + +; CHECK: Loop bb: backedge-taken count is ((-1 + %n) /u 2) +; CHECK: Loop bb: max backedge-taken count is 1073741823