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Enhance induction variable code to remove the

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sext around sext(shorter IV + constant), using a
longer IV instead, when it can figure out the
add can't overflow.  This comes up a lot in
subscripting; mainly affects 64 bit.

llvm-svn: 69123
This commit is contained in:
Dale Johannesen 2009-04-15 01:10:12 +00:00
parent bd35a81da5
commit 427e9aade9
2 changed files with 235 additions and 40 deletions
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161
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -467,8 +467,12 @@ static const Type *getEffectiveIndvarType(const PHINode *Phi) {
/// 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 and NoUnsignedWrap
/// variables to true when appropriate (they are not set to false here),
/// return the PHI for this induction variable. Also record the initial
/// and final values and the increment; these are not meaningful unless
/// either NoSignedWrap or NoUnsignedWrap is true, and are always meaningful
/// in that case, although the final value may be 0 indicating a nonconstant.
///
/// TODO: This duplicates a fair amount of ScalarEvolution logic.
/// Perhaps this can be merged with
@ -479,7 +483,10 @@ static const PHINode *TestOrigIVForWrap(const Loop *L,
const BranchInst *BI,
const Instruction *OrigCond,
bool &NoSignedWrap,
bool &NoUnsignedWrap) {
bool &NoUnsignedWrap,
const ConstantInt* &InitialVal,
const ConstantInt* &IncrVal,
const ConstantInt* &LimitVal) {
// Verify that the loop is sane and find the exit condition.
const ICmpInst *Cmp = dyn_cast<ICmpInst>(OrigCond);
if (!Cmp) return 0;
@ -542,31 +549,31 @@ static const PHINode *TestOrigIVForWrap(const Loop *L,
// Get the increment instruction. Look past casts if we will
// be able to prove that the original induction variable doesn't
// undergo signed or unsigned overflow, respectively.
const Value *IncrVal = CmpLHS;
const Value *IncrInst = CmpLHS;
if (isSigned) {
if (const SExtInst *SI = dyn_cast<SExtInst>(CmpLHS)) {
if (!isa<ConstantInt>(CmpRHS) ||
!cast<ConstantInt>(CmpRHS)->getValue()
.isSignedIntN(IncrVal->getType()->getPrimitiveSizeInBits()))
.isSignedIntN(IncrInst->getType()->getPrimitiveSizeInBits()))
return 0;
IncrVal = SI->getOperand(0);
IncrInst = SI->getOperand(0);
}
} else {
if (const ZExtInst *ZI = dyn_cast<ZExtInst>(CmpLHS)) {
if (!isa<ConstantInt>(CmpRHS) ||
!cast<ConstantInt>(CmpRHS)->getValue()
.isIntN(IncrVal->getType()->getPrimitiveSizeInBits()))
.isIntN(IncrInst->getType()->getPrimitiveSizeInBits()))
return 0;
IncrVal = ZI->getOperand(0);
IncrInst = ZI->getOperand(0);
}
}
// For now, only analyze induction variables that have simple increments.
const BinaryOperator *IncrOp = dyn_cast<BinaryOperator>(IncrVal);
if (!IncrOp ||
IncrOp->getOpcode() != Instruction::Add ||
!isa<ConstantInt>(IncrOp->getOperand(1)) ||
!cast<ConstantInt>(IncrOp->getOperand(1))->equalsInt(1))
const BinaryOperator *IncrOp = dyn_cast<BinaryOperator>(IncrInst);
if (!IncrOp || IncrOp->getOpcode() != Instruction::Add)
return 0;
IncrVal = dyn_cast<ConstantInt>(IncrOp->getOperand(1));
if (!IncrVal)
return 0;
// Make sure the PHI looks like a normal IV.
@ -584,21 +591,78 @@ static const PHINode *TestOrigIVForWrap(const Loop *L,
// For now, only analyze loops with a constant start value, so that
// we can easily determine if the start value is not a maximum value
// which would wrap on the first iteration.
const ConstantInt *InitialVal =
dyn_cast<ConstantInt>(PN->getIncomingValue(IncomingEdge));
InitialVal = dyn_cast<ConstantInt>(PN->getIncomingValue(IncomingEdge));
if (!InitialVal)
return 0;
// 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.
// The upper limit need not be a constant; we'll check later.
LimitVal = dyn_cast<ConstantInt>(CmpRHS);
// We detect the impossibility of wrapping in two cases, both of
// which require starting with a non-max value:
// - The IV counts up by one, and the loop iterates only while it remains
// less than a limiting value (any) in the same type.
// - The IV counts up by a positive increment other than 1, and the
// constant limiting value + the increment is less than the max value
// (computed as max-increment to avoid overflow)
if (isSigned && !InitialVal->getValue().isMaxSignedValue()) {
NoSignedWrap = true;
} else if (!isSigned && !InitialVal->getValue().isMaxValue())
NoUnsignedWrap = true;
if (IncrVal->equalsInt(1))
NoSignedWrap = true; // LimitVal need not be constant
else if (LimitVal) {
uint64_t numBits = LimitVal->getValue().getBitWidth();
if (IncrVal->getValue().sgt(APInt::getNullValue(numBits)) &&
(APInt::getSignedMaxValue(numBits) - IncrVal->getValue())
.sgt(LimitVal->getValue()))
NoSignedWrap = true;
}
} else if (!isSigned && !InitialVal->getValue().isMaxValue()) {
if (IncrVal->equalsInt(1))
NoUnsignedWrap = true; // LimitVal need not be constant
else if (LimitVal) {
uint64_t numBits = LimitVal->getValue().getBitWidth();
if (IncrVal->getValue().ugt(APInt::getNullValue(numBits)) &&
(APInt::getMaxValue(numBits) - IncrVal->getValue())
.ugt(LimitVal->getValue()))
NoUnsignedWrap = true;
}
}
return PN;
}
static Value *getSignExtendedTruncVar(const SCEVAddRecExpr *AR,
ScalarEvolution *SE,
const Type *LargestType, Loop *L,
const Type *myType,
SCEVExpander &Rewriter,
BasicBlock::iterator InsertPt) {
SCEVHandle ExtendedStart =
SE->getSignExtendExpr(AR->getStart(), LargestType);
SCEVHandle ExtendedStep =
SE->getSignExtendExpr(AR->getStepRecurrence(*SE), LargestType);
SCEVHandle ExtendedAddRec =
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
if (LargestType != myType)
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, myType);
return Rewriter.expandCodeFor(ExtendedAddRec, InsertPt);
}
static Value *getZeroExtendedTruncVar(const SCEVAddRecExpr *AR,
ScalarEvolution *SE,
const Type *LargestType, Loop *L,
const Type *myType,
SCEVExpander &Rewriter,
BasicBlock::iterator InsertPt) {
SCEVHandle ExtendedStart =
SE->getZeroExtendExpr(AR->getStart(), LargestType);
SCEVHandle ExtendedStep =
SE->getZeroExtendExpr(AR->getStepRecurrence(*SE), LargestType);
SCEVHandle ExtendedAddRec =
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
if (LargestType != myType)
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, myType);
return Rewriter.expandCodeFor(ExtendedAddRec, InsertPt);
}
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
@ -680,6 +744,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// using it. We can currently only handle loops with a single exit.
bool NoSignedWrap = false;
bool NoUnsignedWrap = false;
const ConstantInt* InitialVal, * IncrVal, * LimitVal;
const PHINode *OrigControllingPHI = 0;
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock)
// Can't rewrite non-branch yet.
@ -688,7 +753,8 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// Determine if the OrigIV will ever undergo overflow.
OrigControllingPHI =
TestOrigIVForWrap(L, BI, OrigCond,
NoSignedWrap, NoUnsignedWrap);
NoSignedWrap, NoUnsignedWrap,
InitialVal, IncrVal, LimitVal);
// We'll be replacing the original condition, so it'll be dead.
DeadInsts.insert(OrigCond);
@ -733,29 +799,44 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end();
UI != UE; ++UI) {
if (isa<SExtInst>(UI) && NoSignedWrap) {
SCEVHandle ExtendedStart =
SE->getSignExtendExpr(AR->getStart(), LargestType);
SCEVHandle ExtendedStep =
SE->getSignExtendExpr(AR->getStepRecurrence(*SE), LargestType);
SCEVHandle ExtendedAddRec =
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
if (LargestType != UI->getType())
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, UI->getType());
Value *TruncIndVar = Rewriter.expandCodeFor(ExtendedAddRec, InsertPt);
Value *TruncIndVar = getSignExtendedTruncVar(AR, SE, LargestType, L,
UI->getType(), Rewriter, InsertPt);
UI->replaceAllUsesWith(TruncIndVar);
if (Instruction *DeadUse = dyn_cast<Instruction>(*UI))
DeadInsts.insert(DeadUse);
}
// See if we can figure out sext(i+constant) doesn't wrap, so we can
// use a larger add. This is common in subscripting.
Instruction *UInst = dyn_cast<Instruction>(*UI);
if (UInst && UInst->getOpcode()==Instruction::Add &&
UInst->hasOneUse() &&
isa<ConstantInt>(UInst->getOperand(1)) &&
isa<SExtInst>(UInst->use_begin()) && NoSignedWrap && LimitVal) {
uint64_t numBits = LimitVal->getValue().getBitWidth();
ConstantInt* RHS = dyn_cast<ConstantInt>(UInst->getOperand(1));
if (((APInt::getSignedMaxValue(numBits) - IncrVal->getValue()) -
RHS->getValue()).sgt(LimitVal->getValue())) {
SExtInst* oldSext = dyn_cast<SExtInst>(UInst->use_begin());
Value *TruncIndVar = getSignExtendedTruncVar(AR, SE, LargestType, L,
oldSext->getType(), Rewriter,
InsertPt);
APInt APcopy = APInt(RHS->getValue());
ConstantInt* newRHS =
ConstantInt::get(APcopy.sext(oldSext->getType()->
getPrimitiveSizeInBits()));
Value *NewAdd = BinaryOperator::CreateAdd(TruncIndVar, newRHS,
UInst->getName()+".nosex",
UInst);
oldSext->replaceAllUsesWith(NewAdd);
if (Instruction *DeadUse = dyn_cast<Instruction>(oldSext))
DeadInsts.insert(DeadUse);
if (Instruction *DeadUse = dyn_cast<Instruction>(UInst))
DeadInsts.insert(DeadUse);
}
}
if (isa<ZExtInst>(UI) && NoUnsignedWrap) {
SCEVHandle ExtendedStart =
SE->getZeroExtendExpr(AR->getStart(), LargestType);
SCEVHandle ExtendedStep =
SE->getZeroExtendExpr(AR->getStepRecurrence(*SE), LargestType);
SCEVHandle ExtendedAddRec =
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
if (LargestType != UI->getType())
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, UI->getType());
Value *TruncIndVar = Rewriter.expandCodeFor(ExtendedAddRec, InsertPt);
Value *TruncIndVar = getZeroExtendedTruncVar(AR, SE, LargestType, L,
UI->getType(), Rewriter, InsertPt);
UI->replaceAllUsesWith(TruncIndVar);
if (Instruction *DeadUse = dyn_cast<Instruction>(*UI))
DeadInsts.insert(DeadUse);

114
test/Transforms/IndVarSimplify/2009-04-14-shorten_iv_vars.ll Normal file
View File

@ -0,0 +1,114 @@
; RUN: llvm-as < %s | opt -indvars | llvm-dis | not grep {sext}
; ModuleID = '<stdin>'
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"
target triple = "x86_64-apple-darwin9.6"
@a = external global i32* ; <i32**> [#uses=3]
@b = external global i32* ; <i32**> [#uses=3]
@c = external global i32* ; <i32**> [#uses=3]
@d = external global i32* ; <i32**> [#uses=3]
@e = external global i32* ; <i32**> [#uses=3]
@f = external global i32* ; <i32**> [#uses=3]
define void @foo() nounwind {
bb1.thread:
br label %bb1
bb1: ; preds = %bb1, %bb1.thread
%i.0.reg2mem.0 = phi i32 [ 0, %bb1.thread ], [ %84, %bb1 ] ; <i32> [#uses=19]
%0 = load i32** @a, align 8 ; <i32*> [#uses=1]
%1 = load i32** @b, align 8 ; <i32*> [#uses=1]
%2 = sext i32 %i.0.reg2mem.0 to i64 ; <i64> [#uses=1]
%3 = getelementptr i32* %1, i64 %2 ; <i32*> [#uses=1]
%4 = load i32* %3, align 1 ; <i32> [#uses=1]
%5 = load i32** @c, align 8 ; <i32*> [#uses=1]
%6 = sext i32 %i.0.reg2mem.0 to i64 ; <i64> [#uses=1]
%7 = getelementptr i32* %5, i64 %6 ; <i32*> [#uses=1]
%8 = load i32* %7, align 1 ; <i32> [#uses=1]
%9 = add i32 %8, %4 ; <i32> [#uses=1]
%10 = sext i32 %i.0.reg2mem.0 to i64 ; <i64> [#uses=1]
%11 = getelementptr i32* %0, i64 %10 ; <i32*> [#uses=1]
store i32 %9, i32* %11, align 1
%12 = load i32** @a, align 8 ; <i32*> [#uses=1]
%13 = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=1]
%14 = load i32** @b, align 8 ; <i32*> [#uses=1]
%15 = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=1]
%16 = sext i32 %15 to i64 ; <i64> [#uses=1]
%17 = getelementptr i32* %14, i64 %16 ; <i32*> [#uses=1]
%18 = load i32* %17, align 1 ; <i32> [#uses=1]
%19 = load i32** @c, align 8 ; <i32*> [#uses=1]
%20 = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=1]
%21 = sext i32 %20 to i64 ; <i64> [#uses=1]
%22 = getelementptr i32* %19, i64 %21 ; <i32*> [#uses=1]
%23 = load i32* %22, align 1 ; <i32> [#uses=1]
%24 = add i32 %23, %18 ; <i32> [#uses=1]
%25 = sext i32 %13 to i64 ; <i64> [#uses=1]
%26 = getelementptr i32* %12, i64 %25 ; <i32*> [#uses=1]
store i32 %24, i32* %26, align 1
%27 = load i32** @a, align 8 ; <i32*> [#uses=1]
%28 = add i32 %i.0.reg2mem.0, 2 ; <i32> [#uses=1]
%29 = load i32** @b, align 8 ; <i32*> [#uses=1]
%30 = add i32 %i.0.reg2mem.0, 2 ; <i32> [#uses=1]
%31 = sext i32 %30 to i64 ; <i64> [#uses=1]
%32 = getelementptr i32* %29, i64 %31 ; <i32*> [#uses=1]
%33 = load i32* %32, align 1 ; <i32> [#uses=1]
%34 = load i32** @c, align 8 ; <i32*> [#uses=1]
%35 = add i32 %i.0.reg2mem.0, 2 ; <i32> [#uses=1]
%36 = sext i32 %35 to i64 ; <i64> [#uses=1]
%37 = getelementptr i32* %34, i64 %36 ; <i32*> [#uses=1]
%38 = load i32* %37, align 1 ; <i32> [#uses=1]
%39 = add i32 %38, %33 ; <i32> [#uses=1]
%40 = sext i32 %28 to i64 ; <i64> [#uses=1]
%41 = getelementptr i32* %27, i64 %40 ; <i32*> [#uses=1]
store i32 %39, i32* %41, align 1
%42 = load i32** @d, align 8 ; <i32*> [#uses=1]
%43 = load i32** @e, align 8 ; <i32*> [#uses=1]
%44 = sext i32 %i.0.reg2mem.0 to i64 ; <i64> [#uses=1]
%45 = getelementptr i32* %43, i64 %44 ; <i32*> [#uses=1]
%46 = load i32* %45, align 1 ; <i32> [#uses=1]
%47 = load i32** @f, align 8 ; <i32*> [#uses=1]
%48 = sext i32 %i.0.reg2mem.0 to i64 ; <i64> [#uses=1]
%49 = getelementptr i32* %47, i64 %48 ; <i32*> [#uses=1]
%50 = load i32* %49, align 1 ; <i32> [#uses=1]
%51 = add i32 %50, %46 ; <i32> [#uses=1]
%52 = sext i32 %i.0.reg2mem.0 to i64 ; <i64> [#uses=1]
%53 = getelementptr i32* %42, i64 %52 ; <i32*> [#uses=1]
store i32 %51, i32* %53, align 1
%54 = load i32** @d, align 8 ; <i32*> [#uses=1]
%55 = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=1]
%56 = load i32** @e, align 8 ; <i32*> [#uses=1]
%57 = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=1]
%58 = sext i32 %57 to i64 ; <i64> [#uses=1]
%59 = getelementptr i32* %56, i64 %58 ; <i32*> [#uses=1]
%60 = load i32* %59, align 1 ; <i32> [#uses=1]
%61 = load i32** @f, align 8 ; <i32*> [#uses=1]
%62 = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=1]
%63 = sext i32 %62 to i64 ; <i64> [#uses=1]
%64 = getelementptr i32* %61, i64 %63 ; <i32*> [#uses=1]
%65 = load i32* %64, align 1 ; <i32> [#uses=1]
%66 = add i32 %65, %60 ; <i32> [#uses=1]
%67 = sext i32 %55 to i64 ; <i64> [#uses=1]
%68 = getelementptr i32* %54, i64 %67 ; <i32*> [#uses=1]
store i32 %66, i32* %68, align 1
%69 = load i32** @d, align 8 ; <i32*> [#uses=1]
%70 = add i32 %i.0.reg2mem.0, 2 ; <i32> [#uses=1]
%71 = load i32** @e, align 8 ; <i32*> [#uses=1]
%72 = add i32 %i.0.reg2mem.0, 2 ; <i32> [#uses=1]
%73 = sext i32 %72 to i64 ; <i64> [#uses=1]
%74 = getelementptr i32* %71, i64 %73 ; <i32*> [#uses=1]
%75 = load i32* %74, align 1 ; <i32> [#uses=1]
%76 = load i32** @f, align 8 ; <i32*> [#uses=1]
%77 = add i32 %i.0.reg2mem.0, 2 ; <i32> [#uses=1]
%78 = sext i32 %77 to i64 ; <i64> [#uses=1]
%79 = getelementptr i32* %76, i64 %78 ; <i32*> [#uses=1]
%80 = load i32* %79, align 1 ; <i32> [#uses=1]
%81 = add i32 %80, %75 ; <i32> [#uses=1]
%82 = sext i32 %70 to i64 ; <i64> [#uses=1]
%83 = getelementptr i32* %69, i64 %82 ; <i32*> [#uses=1]
store i32 %81, i32* %83, align 1
%84 = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=2]
%85 = icmp sgt i32 %84, 23646 ; <i1> [#uses=1]
br i1 %85, label %return, label %bb1
return: ; preds = %bb1
ret void
}