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Fix ScalarEvolution's tripcount computation for chains of loops

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where each loop's induction variable's start value is the exit
value of a preceding loop.

llvm-svn: 107224
This commit is contained in:
Dan Gohman 2010-06-29 23:43:06 +00:00
parent 5823da3ab0
commit ae36b1ed42
2 changed files with 125 additions and 43 deletions
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102
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -4337,54 +4337,51 @@ const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
// the arguments into constants, and if so, try to constant propagate the
// result. This is particularly useful for computing loop exit values.
if (CanConstantFold(I)) {
std::vector<Constant*> Operands;
Operands.reserve(I->getNumOperands());
SmallVector<Constant *, 4> Operands;
bool MadeImprovement = false;
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
Value *Op = I->getOperand(i);
if (Constant *C = dyn_cast<Constant>(Op)) {
Operands.push_back(C);
} else {
// If any of the operands is non-constant and if they are
// non-integer and non-pointer, don't even try to analyze them
// with scev techniques.
if (!isSCEVable(Op->getType()))
return V;
const SCEV *OpV = getSCEVAtScope(Op, L);
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(OpV)) {
Constant *C = SC->getValue();
if (C->getType() != Op->getType())
C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
Op->getType(),
false),
C, Op->getType());
Operands.push_back(C);
} else if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(OpV)) {
if (Constant *C = dyn_cast<Constant>(SU->getValue())) {
if (C->getType() != Op->getType())
C =
ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
Op->getType(),
false),
C, Op->getType());
Operands.push_back(C);
} else
return V;
} else {
return V;
}
continue;
}
// If any of the operands is non-constant and if they are
// non-integer and non-pointer, don't even try to analyze them
// with scev techniques.
if (!isSCEVable(Op->getType()))
return V;
const SCEV *OrigV = getSCEV(Op);
const SCEV *OpV = getSCEVAtScope(OrigV, L);
MadeImprovement |= OrigV != OpV;
Constant *C = 0;
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(OpV))
C = SC->getValue();
if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(OpV))
C = dyn_cast<Constant>(SU->getValue());
if (!C) return V;
if (C->getType() != Op->getType())
C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
Op->getType(),
false),
C, Op->getType());
Operands.push_back(C);
}
Constant *C = 0;
if (const CmpInst *CI = dyn_cast<CmpInst>(I))
C = ConstantFoldCompareInstOperands(CI->getPredicate(),
Operands[0], Operands[1], TD);
else
C = ConstantFoldInstOperands(I->getOpcode(), I->getType(),
&Operands[0], Operands.size(), TD);
if (C)
// Check to see if getSCEVAtScope actually made an improvement.
if (MadeImprovement) {
Constant *C = 0;
if (const CmpInst *CI = dyn_cast<CmpInst>(I))
C = ConstantFoldCompareInstOperands(CI->getPredicate(),
Operands[0], Operands[1], TD);
else
C = ConstantFoldInstOperands(I->getOpcode(), I->getType(),
&Operands[0], Operands.size(), TD);
if (!C) return V;
return getSCEV(C);
}
}
}
@ -4434,7 +4431,29 @@ const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
// If this is a loop recurrence for a loop that does not contain L, then we
// are dealing with the final value computed by the loop.
if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(V)) {
if (!L || !AddRec->getLoop()->contains(L)) {
// First, attempt to evaluate each operand.
// Avoid performing the look-up in the common case where the specified
// expression has no loop-variant portions.
for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) {
const SCEV *OpAtScope = getSCEVAtScope(AddRec->getOperand(i), L);
if (OpAtScope == AddRec->getOperand(i))
continue;
// Okay, at least one of these operands is loop variant but might be
// foldable. Build a new instance of the folded commutative expression.
SmallVector<const SCEV *, 8> NewOps(AddRec->op_begin(),
AddRec->op_begin()+i);
NewOps.push_back(OpAtScope);
for (++i; i != e; ++i)
NewOps.push_back(getSCEVAtScope(AddRec->getOperand(i), L));
AddRec = cast<SCEVAddRecExpr>(getAddRecExpr(NewOps, AddRec->getLoop()));
break;
}
// If the scope is outside the addrec's loop, evaluate it by using the
// loop exit value of the addrec.
if (!AddRec->getLoop()->contains(L)) {
// To evaluate this recurrence, we need to know how many times the AddRec
// loop iterates. Compute this now.
const SCEV *BackedgeTakenCount = getBackedgeTakenCount(AddRec->getLoop());
@ -4443,6 +4462,7 @@ const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
// Then, evaluate the AddRec.
return AddRec->evaluateAtIteration(BackedgeTakenCount, *this);
}
return AddRec;
}

66
llvm/test/Transforms/IndVarSimplify/tripcount_compute.ll
View File

@ -1,9 +1,12 @@
; RUN: opt < %s -indvars -S | FileCheck %s
; These tests ensure that we can compute the trip count of various forms of
; loops. If the trip count of the loop is computable, then we will know what
; the exit value of the loop will be for some value, allowing us to substitute
; it directly into users outside of the loop, making the loop dead.
;
; RUN: opt < %s -indvars -loop-deletion -simplifycfg -S | not grep br
; CHECK: @linear_setne
; CHECK: ret i32 100
define i32 @linear_setne() {
entry:
@ -19,6 +22,9 @@ loopexit: ; preds = %loop
ret i32 %i
}
; CHECK: @linear_setne_2
; CHECK: ret i32 100
define i32 @linear_setne_2() {
entry:
br label %loop
@ -33,6 +39,9 @@ loopexit: ; preds = %loop
ret i32 %i
}
; CHECK: @linear_setne_overflow
; CHECK: ret i32 0
define i32 @linear_setne_overflow() {
entry:
br label %loop
@ -47,6 +56,9 @@ loopexit: ; preds = %loop
ret i32 %i
}
; CHECK: @linear_setlt
; CHECK: ret i32 100
define i32 @linear_setlt() {
entry:
br label %loop
@ -61,6 +73,9 @@ loopexit: ; preds = %loop
ret i32 %i
}
; CHECK: @quadratic_setlt
; CHECK: ret i32 34
define i32 @quadratic_setlt() {
entry:
br label %loop
@ -76,6 +91,9 @@ loopexit: ; preds = %loop
ret i32 %i
}
; CHECK: @chained
; CHECK: ret i32 200
define i32 @chained() {
entry:
br label %loop
@ -98,3 +116,47 @@ loop2: ; preds = %loop2, %loopexit
loopexit2: ; preds = %loop2
ret i32 %j
}
; CHECK: @chained4
; CHECK: ret i32 400
define i32 @chained4() {
entry:
br label %loop
loop: ; preds = %loop, %entry
%i = phi i32 [ 0, %entry ], [ %i.next, %loop ] ; <i32> [#uses=3]
%i.next = add i32 %i, 1 ; <i32> [#uses=1]
%c = icmp ne i32 %i.next, 100 ; <i1> [#uses=1]
br i1 %c, label %loop, label %loopexit
loopexit: ; preds = %loop
br label %loop2
loop2: ; preds = %loop2, %loopexit
%j = phi i32 [ %i.next, %loopexit ], [ %j.next, %loop2 ] ; <i32> [#uses=3]
%j.next = add i32 %j, 1 ; <i32> [#uses=1]
%c2 = icmp ne i32 %j.next, 200 ; <i1> [#uses=1]
br i1 %c2, label %loop2, label %loopexit2
loopexit2: ; preds = %loop
br label %loop8
loop8: ; preds = %loop2, %loopexit
%k = phi i32 [ %j.next, %loopexit2 ], [ %k.next, %loop8 ] ; <i32> [#uses=3]
%k.next = add i32 %k, 1 ; <i32> [#uses=1]
%c8 = icmp ne i32 %k.next, 300 ; <i1> [#uses=1]
br i1 %c8, label %loop8, label %loopexit8
loopexit8: ; preds = %loop2
br label %loop9
loop9: ; preds = %loop2, %loopexit
%l = phi i32 [ %k.next, %loopexit8 ], [ %l.next, %loop9 ] ; <i32> [#uses=3]
%l.next = add i32 %l, 1 ; <i32> [#uses=1]
%c9 = icmp ne i32 %l.next, 400 ; <i1> [#uses=1]
br i1 %c9, label %loop9, label %loopexit9
loopexit9: ; preds = %loop2
ret i32 %l.next
}