[llvm-commits] [llvm] r64918 - in /llvm/trunk: include/llvm/Analysis/ScalarEvolution.h lib/Analysis/ScalarEvolution.cpp lib/Transforms/Scalar/IndVarSimplify.cpp test/Transforms/IndVarSimplify/preserve-signed-wrap.ll test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll test/Transforms/IndVarSimplify/signed-trip-count.ll
Chris Lattner
clattner at apple.com
Wed Feb 18 10:07:49 PST 2009
On Feb 18, 2009, at 9:22 AM, Dan Gohman wrote:
> Author: djg
> Date: Wed Feb 18 11:22:41 2009
> New Revision: 64918
>
> URL: http://llvm.org/viewvc/llvm-project?rev=64918&view=rev
> Log:
> 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.
Dan, I'm concerned about this. Sign extensions are generally more
expensive than zero extensions, and much of the optimizer
canonicalizes sign extends to zero extends.
-Chris
>
>
> Add a getTruncateOrSignExtend method to ScalarEvolution,
> following getTruncateOrZeroExtend.
>
> Added:
> llvm/trunk/test/Transforms/IndVarSimplify/signed-trip-count.ll
> Modified:
> llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
> llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
> llvm/trunk/test/Transforms/IndVarSimplify/preserve-signed-wrap.ll
> llvm/trunk/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-
> casts.ll
>
> Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ScalarEvolution.h?rev=64918&r1=64917&r2=64918&view=diff
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
> +++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Wed Feb 18
> 11:22:41 2009
> @@ -264,6 +264,11 @@
> /// extended, it is zero extended.
> SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const
> Type *Ty);
>
> + /// getTruncateOrSignExtend - Return a SCEV corresponding to a
> conversion
> + /// of the input value to the specified type. If the type must
> be
> + /// extended, it is sign extended.
> + SCEVHandle getTruncateOrSignExtend(const SCEVHandle &V, const
> Type *Ty);
> +
> /// getIntegerSCEV - Given an integer or FP type, create a
> constant for the
> /// specified signed integer value and return a SCEV for the
> constant.
> SCEVHandle getIntegerSCEV(int Val, const Type *Ty);
>
> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=64918&r1=64917&r2=64918&view=diff
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed Feb 18 11:22:41
> 2009
> @@ -755,6 +755,21 @@
> return getZeroExtendExpr(V, Ty);
> }
>
> +/// getTruncateOrSignExtend - Return a SCEV corresponding to a
> conversion
> +/// of the input value to the specified type. If the type must be
> +/// extended, it is sign extended.
> +SCEVHandle ScalarEvolution::getTruncateOrSignExtend(const
> SCEVHandle &V,
> + const Type *Ty) {
> + const Type *SrcTy = V->getType();
> + assert(SrcTy->isInteger() && Ty->isInteger() &&
> + "Cannot truncate or sign extend with non-integer
> arguments!");
> + if (SrcTy->getPrimitiveSizeInBits() == Ty-
> >getPrimitiveSizeInBits())
> + return V; // No conversion
> + if (SrcTy->getPrimitiveSizeInBits() > Ty->getPrimitiveSizeInBits())
> + return getTruncateExpr(V, Ty);
> + return getSignExtendExpr(V, Ty);
> +}
> +
> // get - Get a canonical add expression, or something simpler if
> possible.
> SCEVHandle ScalarEvolution::getAddExpr(std::vector<SCEVHandle> &Ops) {
> assert(!Ops.empty() && "Cannot get empty add!");
>
> Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=64918&r1=64917&r2=64918&view=diff
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Wed Feb 18
> 11:22:41 2009
> @@ -96,7 +96,8 @@
> Value *IndVar,
> BasicBlock *ExitingBlock,
> BranchInst *BI,
> - SCEVExpander &Rewriter);
> + SCEVExpander &Rewriter,
> + bool SignExtendTripCount);
> void RewriteLoopExitValues(Loop *L, SCEV *IterationCount);
>
> void DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*,
> 16> &Insts);
> @@ -235,7 +236,8 @@
> Value *IndVar,
> BasicBlock *ExitingBlock,
> BranchInst *BI,
> - SCEVExpander &Rewriter) {
> + SCEVExpander &Rewriter,
> + bool SignExtendTripCount) {
> // If the exiting block is not the same as the backedge block, we
> must compare
> // against the preincremented value, otherwise we prefer to
> compare against
> // the post-incremented value.
> @@ -253,11 +255,18 @@
> if ((isa<SCEVConstant>(N) && !N->isZero()) ||
> SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
> // No overflow. Cast the sum.
> - IterationCount = SE->getTruncateOrZeroExtend(N, IndVar-
> >getType());
> + if (SignExtendTripCount)
> + IterationCount = SE->getTruncateOrSignExtend(N, IndVar-
> >getType());
> + else
> + IterationCount = SE->getTruncateOrZeroExtend(N, IndVar-
> >getType());
> } else {
> // Potential overflow. Cast before doing the add.
> - IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
> - IndVar-
> >getType());
> + if (SignExtendTripCount)
> + IterationCount = SE->getTruncateOrSignExtend(IterationCount,
> + IndVar-
> >getType());
> + else
> + IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
> + IndVar-
> >getType());
> IterationCount =
> SE->getAddExpr(IterationCount,
> SE->getIntegerSCEV(1, IndVar->getType()));
> @@ -269,8 +278,12 @@
> CmpIndVar = L->getCanonicalInductionVariableIncrement();
> } else {
> // We have to use the preincremented value...
> - IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
> - IndVar->getType());
> + if (SignExtendTripCount)
> + IterationCount = SE->getTruncateOrSignExtend(IterationCount,
> + IndVar-
> >getType());
> + else
> + IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
> + IndVar-
> >getType());
> CmpIndVar = IndVar;
> }
>
> @@ -464,10 +477,13 @@
>
> /// TestOrigIVForWrap - Analyze the original induction variable
> /// that controls the loop's iteration to determine whether it
> -/// would ever undergo signed or unsigned overflow.
> +/// would ever undergo signed or unsigned overflow. Also, check
> +/// whether an induction variable in the same type that starts
> +/// at 0 would undergo signed overflow.
> ///
> -/// In addition to setting the NoSignedWrap and NoUnsignedWrap
> -/// variables, return the PHI for this induction variable.
> +/// In addition to setting the NoSignedWrap, NoUnsignedWrap, and
> +/// SignExtendTripCount variables, return the PHI for this induction
> +/// variable.
> ///
> /// TODO: This duplicates a fair amount of ScalarEvolution logic.
> /// Perhaps this can be merged with ScalarEvolution::getIterationCount
> @@ -477,7 +493,8 @@
> const BranchInst *BI,
> const Instruction *OrigCond,
> bool &NoSignedWrap,
> - bool &NoUnsignedWrap) {
> + bool &NoUnsignedWrap,
> + bool &SignExtendTripCount) {
> // Verify that the loop is sane and find the exit condition.
> const ICmpInst *Cmp = dyn_cast<ICmpInst>(OrigCond);
> if (!Cmp) return 0;
> @@ -590,9 +607,13 @@
> // The original induction variable will start at some non-max value,
> // it counts up by one, and the loop iterates only while it remans
> // less than some value in the same type. As such, it will never
> wrap.
> - if (isSigned && !InitialVal->getValue().isMaxSignedValue())
> + if (isSigned && !InitialVal->getValue().isMaxSignedValue()) {
> NoSignedWrap = true;
> - else if (!isSigned && !InitialVal->getValue().isMaxValue())
> + // If the original induction variable starts at zero or greater,
> + // the trip count can be considered signed.
> + if (InitialVal->getValue().isNonNegative())
> + SignExtendTripCount = true;
> + } else if (!isSigned && !InitialVal->getValue().isMaxValue())
> NoUnsignedWrap = true;
> return PN;
> }
> @@ -678,6 +699,7 @@
> // using it. We can currently only handle loops with a single exit.
> bool NoSignedWrap = false;
> bool NoUnsignedWrap = false;
> + bool SignExtendTripCount = false;
> const PHINode *OrigControllingPHI = 0;
> if (!isa<SCEVCouldNotCompute>(IterationCount) && ExitingBlock)
> // Can't rewrite non-branch yet.
> @@ -686,14 +708,16 @@
> // Determine if the OrigIV will ever undergo overflow.
> OrigControllingPHI =
> TestOrigIVForWrap(L, BI, OrigCond,
> - NoSignedWrap, NoUnsignedWrap);
> + NoSignedWrap, NoUnsignedWrap,
> + SignExtendTripCount);
>
> // We'll be replacing the original condition, so it'll be
> dead.
> DeadInsts.insert(OrigCond);
> }
>
> LinearFunctionTestReplace(L, IterationCount, IndVar,
> - ExitingBlock, BI, Rewriter);
> + ExitingBlock, BI, Rewriter,
> + SignExtendTripCount);
> }
>
> // Now that we have a canonical induction variable, we can rewrite
> any
>
> Modified: llvm/trunk/test/Transforms/IndVarSimplify/preserve-signed-
> wrap.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/preserve-signed-wrap.ll?rev=64918&r1=64917&r2=64918&view=diff
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/test/Transforms/IndVarSimplify/preserve-signed-
> wrap.ll (original)
> +++ llvm/trunk/test/Transforms/IndVarSimplify/preserve-signed-
> wrap.ll Wed Feb 18 11:22:41 2009
> @@ -1,5 +1,6 @@
> ; RUN: llvm-as < %s | opt -indvars | llvm-dis > %t
> -; RUN: grep sext %t | count 1
> +; RUN: grep sext %t | count 2
> +; RUN: grep { = sext i32 %n to i64} %t
> ; RUN: grep phi %t | count 1
> ; RUN: grep {phi i64} %t
>
>
> Modified: llvm/trunk/test/Transforms/IndVarSimplify/promote-iv-to-
> eliminate-casts.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll?rev=64918&r1=64917&r2=64918&view=diff
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/test/Transforms/IndVarSimplify/promote-iv-to-
> eliminate-casts.ll (original)
> +++ llvm/trunk/test/Transforms/IndVarSimplify/promote-iv-to-
> eliminate-casts.ll Wed Feb 18 11:22:41 2009
> @@ -1,6 +1,7 @@
> -; RUN: llvm-as < %s | opt -indvars | llvm-dis | not grep sext
> -
> -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"
> +; RUN: llvm-as < %s | opt -indvars | llvm-dis > %t
> +; RUN: grep sext %t | count 2
> +; RUN: grep { = sext i16 %N to i64} %t
> +; RUN: grep { = sext i32 %count to i64} %t
>
> define i64 @test(i64* nocapture %first, i32 %count) nounwind
> readonly {
> entry:
>
> Added: llvm/trunk/test/Transforms/IndVarSimplify/signed-trip-count.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/signed-trip-count.ll?rev=64918&view=auto
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/test/Transforms/IndVarSimplify/signed-trip-count.ll
> (added)
> +++ llvm/trunk/test/Transforms/IndVarSimplify/signed-trip-count.ll
> Wed Feb 18 11:22:41 2009
> @@ -0,0 +1,31 @@
> +; RUN: llvm-as < %s | opt -indvars | llvm-dis > %t
> +; RUN: grep { = sext i32 %n} %t
> +; RUN: grep phi %t | count 1
> +; RUN: not grep zext %t
> +
> +define void @foo(i64* nocapture %x, i32 %n) nounwind {
> +entry:
> + %tmp102 = icmp sgt i32 %n, 0 ; <i1> [#uses=1]
> + br i1 %tmp102, label %bb.nph, label %return
> +
> +bb.nph: ; preds = %entry
> + br label %bb
> +
> +bb: ; preds = %bb7, %bb.nph
> + %i.01 = phi i32 [ %tmp6, %bb7 ], [ 0, %bb.nph ] ; <i32> [#uses=3]
> + %tmp1 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
> + %tmp4 = getelementptr i64* %x, i32 %i.01 ; <i64*> [#uses=1]
> + store i64 %tmp1, i64* %tmp4, align 8
> + %tmp6 = add i32 %i.01, 1 ; <i32> [#uses=2]
> + br label %bb7
> +
> +bb7: ; preds = %bb
> + %tmp10 = icmp slt i32 %tmp6, %n ; <i1> [#uses=1]
> + br i1 %tmp10, label %bb, label %bb7.return_crit_edge
> +
> +bb7.return_crit_edge: ; preds = %bb7
> + br label %return
> +
> +return: ; preds = %bb7.return_crit_edge, %entry
> + ret void
> +}
>
>
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