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Use a sign-extend instead of a zero-extend when promoting a
trip count value when the original loop iteration condition is signed and the canonical induction variable won't undergo signed overflow. This isn't required for correctness; it just preserves more information about original loop iteration values. Add a getTruncateOrSignExtend method to ScalarEvolution, following getTruncateOrZeroExtend. llvm-svn: 64918
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@ -264,6 +264,11 @@ namespace llvm {
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/// extended, it is zero extended.
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SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const Type *Ty);
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/// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion
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/// of the input value to the specified type. If the type must be
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/// extended, it is sign extended.
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SCEVHandle getTruncateOrSignExtend(const SCEVHandle &V, const Type *Ty);
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/// getIntegerSCEV - Given an integer or FP type, create a constant for the
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/// specified signed integer value and return a SCEV for the constant.
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SCEVHandle getIntegerSCEV(int Val, const Type *Ty);
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@ -755,6 +755,21 @@ SCEVHandle ScalarEvolution::getTruncateOrZeroExtend(const SCEVHandle &V,
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return getZeroExtendExpr(V, Ty);
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}
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/// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion
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/// of the input value to the specified type. If the type must be
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/// extended, it is sign extended.
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SCEVHandle ScalarEvolution::getTruncateOrSignExtend(const SCEVHandle &V,
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const Type *Ty) {
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const Type *SrcTy = V->getType();
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assert(SrcTy->isInteger() && Ty->isInteger() &&
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"Cannot truncate or sign extend with non-integer arguments!");
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if (SrcTy->getPrimitiveSizeInBits() == Ty->getPrimitiveSizeInBits())
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return V; // No conversion
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if (SrcTy->getPrimitiveSizeInBits() > Ty->getPrimitiveSizeInBits())
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return getTruncateExpr(V, Ty);
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return getSignExtendExpr(V, Ty);
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}
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// get - Get a canonical add expression, or something simpler if possible.
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SCEVHandle ScalarEvolution::getAddExpr(std::vector<SCEVHandle> &Ops) {
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assert(!Ops.empty() && "Cannot get empty add!");
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@ -96,7 +96,8 @@ namespace {
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Value *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter);
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SCEVExpander &Rewriter,
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bool SignExtendTripCount);
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void RewriteLoopExitValues(Loop *L, SCEV *IterationCount);
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void DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*, 16> &Insts);
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@ -235,7 +236,8 @@ void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
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Value *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter) {
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SCEVExpander &Rewriter,
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bool SignExtendTripCount) {
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// If the exiting block is not the same as the backedge block, we must compare
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// against the preincremented value, otherwise we prefer to compare against
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// the post-incremented value.
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@ -253,11 +255,18 @@ void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
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if ((isa<SCEVConstant>(N) && !N->isZero()) ||
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SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
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// No overflow. Cast the sum.
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IterationCount = SE->getTruncateOrZeroExtend(N, IndVar->getType());
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if (SignExtendTripCount)
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IterationCount = SE->getTruncateOrSignExtend(N, IndVar->getType());
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else
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IterationCount = SE->getTruncateOrZeroExtend(N, IndVar->getType());
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} else {
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// Potential overflow. Cast before doing the add.
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IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
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IndVar->getType());
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if (SignExtendTripCount)
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IterationCount = SE->getTruncateOrSignExtend(IterationCount,
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IndVar->getType());
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else
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IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
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IndVar->getType());
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IterationCount =
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SE->getAddExpr(IterationCount,
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SE->getIntegerSCEV(1, IndVar->getType()));
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@ -269,8 +278,12 @@ void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
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CmpIndVar = L->getCanonicalInductionVariableIncrement();
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} else {
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// We have to use the preincremented value...
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IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
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IndVar->getType());
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if (SignExtendTripCount)
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IterationCount = SE->getTruncateOrSignExtend(IterationCount,
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IndVar->getType());
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else
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IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
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IndVar->getType());
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CmpIndVar = IndVar;
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}
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@ -464,10 +477,13 @@ static const Type *getEffectiveIndvarType(const PHINode *Phi) {
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/// TestOrigIVForWrap - Analyze the original induction variable
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/// that controls the loop's iteration to determine whether it
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/// would ever undergo signed or unsigned overflow.
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/// would ever undergo signed or unsigned overflow. Also, check
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/// whether an induction variable in the same type that starts
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/// at 0 would undergo signed overflow.
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///
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/// In addition to setting the NoSignedWrap and NoUnsignedWrap
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/// variables, return the PHI for this induction variable.
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/// In addition to setting the NoSignedWrap, NoUnsignedWrap, and
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/// SignExtendTripCount variables, return the PHI for this induction
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/// variable.
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///
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/// TODO: This duplicates a fair amount of ScalarEvolution logic.
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/// Perhaps this can be merged with ScalarEvolution::getIterationCount
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@ -477,7 +493,8 @@ static const PHINode *TestOrigIVForWrap(const Loop *L,
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const BranchInst *BI,
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const Instruction *OrigCond,
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bool &NoSignedWrap,
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bool &NoUnsignedWrap) {
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bool &NoUnsignedWrap,
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bool &SignExtendTripCount) {
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// Verify that the loop is sane and find the exit condition.
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const ICmpInst *Cmp = dyn_cast<ICmpInst>(OrigCond);
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if (!Cmp) return 0;
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@ -590,9 +607,13 @@ static const PHINode *TestOrigIVForWrap(const Loop *L,
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// The original induction variable will start at some non-max value,
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// it counts up by one, and the loop iterates only while it remans
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// less than some value in the same type. As such, it will never wrap.
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if (isSigned && !InitialVal->getValue().isMaxSignedValue())
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if (isSigned && !InitialVal->getValue().isMaxSignedValue()) {
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NoSignedWrap = true;
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else if (!isSigned && !InitialVal->getValue().isMaxValue())
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// If the original induction variable starts at zero or greater,
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// the trip count can be considered signed.
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if (InitialVal->getValue().isNonNegative())
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SignExtendTripCount = true;
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} else if (!isSigned && !InitialVal->getValue().isMaxValue())
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NoUnsignedWrap = true;
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return PN;
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}
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@ -678,6 +699,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
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// using it. We can currently only handle loops with a single exit.
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bool NoSignedWrap = false;
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bool NoUnsignedWrap = false;
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bool SignExtendTripCount = false;
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const PHINode *OrigControllingPHI = 0;
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if (!isa<SCEVCouldNotCompute>(IterationCount) && ExitingBlock)
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// Can't rewrite non-branch yet.
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@ -686,14 +708,16 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
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// Determine if the OrigIV will ever undergo overflow.
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OrigControllingPHI =
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TestOrigIVForWrap(L, BI, OrigCond,
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NoSignedWrap, NoUnsignedWrap);
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NoSignedWrap, NoUnsignedWrap,
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SignExtendTripCount);
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// We'll be replacing the original condition, so it'll be dead.
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DeadInsts.insert(OrigCond);
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}
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LinearFunctionTestReplace(L, IterationCount, IndVar,
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ExitingBlock, BI, Rewriter);
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ExitingBlock, BI, Rewriter,
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SignExtendTripCount);
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}
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// Now that we have a canonical induction variable, we can rewrite any
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@ -1,5 +1,6 @@
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; RUN: llvm-as < %s | opt -indvars | llvm-dis > %t
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; RUN: grep sext %t | count 1
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; RUN: grep sext %t | count 2
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; RUN: grep { = sext i32 %n to i64} %t
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; RUN: grep phi %t | count 1
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; RUN: grep {phi i64} %t
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@ -1,6 +1,7 @@
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; RUN: llvm-as < %s | opt -indvars | llvm-dis | not grep sext
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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"
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; RUN: llvm-as < %s | opt -indvars | llvm-dis > %t
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; RUN: grep sext %t | count 2
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; RUN: grep { = sext i16 %N to i64} %t
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; RUN: grep { = sext i32 %count to i64} %t
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define i64 @test(i64* nocapture %first, i32 %count) nounwind readonly {
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entry:
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31
test/Transforms/IndVarSimplify/signed-trip-count.ll
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31
test/Transforms/IndVarSimplify/signed-trip-count.ll
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@ -0,0 +1,31 @@
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; RUN: llvm-as < %s | opt -indvars | llvm-dis > %t
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; RUN: grep { = sext i32 %n} %t
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; RUN: grep phi %t | count 1
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; RUN: not grep zext %t
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define void @foo(i64* nocapture %x, i32 %n) nounwind {
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entry:
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%tmp102 = icmp sgt i32 %n, 0 ; <i1> [#uses=1]
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br i1 %tmp102, label %bb.nph, label %return
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bb.nph: ; preds = %entry
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br label %bb
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bb: ; preds = %bb7, %bb.nph
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%i.01 = phi i32 [ %tmp6, %bb7 ], [ 0, %bb.nph ] ; <i32> [#uses=3]
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%tmp1 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
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%tmp4 = getelementptr i64* %x, i32 %i.01 ; <i64*> [#uses=1]
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store i64 %tmp1, i64* %tmp4, align 8
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%tmp6 = add i32 %i.01, 1 ; <i32> [#uses=2]
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br label %bb7
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bb7: ; preds = %bb
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%tmp10 = icmp slt i32 %tmp6, %n ; <i1> [#uses=1]
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br i1 %tmp10, label %bb, label %bb7.return_crit_edge
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bb7.return_crit_edge: ; preds = %bb7
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br label %return
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return: ; preds = %bb7.return_crit_edge, %entry
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ret void
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}
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