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Generalize ScalarEvolution's PHI analysis to handle loops that don't

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have preheaders or dedicated exit blocks, as clients may not otherwise
need to run LoopSimplify.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101030 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-04-12 07:49:36 +00:00
parent 646e047765
commit 27dead44e0
2 changed files with 55 additions and 14 deletions
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40
lib/Analysis/ScalarEvolution.cpp
View File

@ -2597,14 +2597,29 @@ ScalarEvolution::ForgetSymbolicName(Instruction *PN, const SCEV *SymName) {
/// a loop header, making it a potential recurrence, or it doesn't.
///
const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
if (PN->getNumIncomingValues() == 2) // The loops have been canonicalized.
if (const Loop *L = LI->getLoopFor(PN->getParent()))
if (L->getHeader() == PN->getParent()) {
// If it lives in the loop header, it has two incoming values, one
// from outside the loop, and one from inside.
unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
unsigned BackEdge = IncomingEdge^1;
if (const Loop *L = LI->getLoopFor(PN->getParent()))
if (L->getHeader() == PN->getParent()) {
// The loop may have multiple entrances or multiple exits; we can analyze
// this phi as an addrec if it has a unique entry value and a unique
// backedge value.
Value *BEValueV = 0, *StartValueV = 0;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *V = PN->getIncomingValue(i);
if (L->contains(PN->getIncomingBlock(i))) {
if (!BEValueV) {
BEValueV = V;
} else if (BEValueV != V) {
BEValueV = 0;
break;
}
} else if (!StartValueV) {
StartValueV = V;
} else if (StartValueV != V) {
StartValueV = 0;
break;
}
}
if (BEValueV && StartValueV) {
// While we are analyzing this PHI node, handle its value symbolically.
const SCEV *SymbolicName = getUnknown(PN);
assert(Scalars.find(PN) == Scalars.end() &&
@ -2613,7 +2628,6 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
// Using this symbolic name for the PHI, analyze the value coming around
// the back-edge.
Value *BEValueV = PN->getIncomingValue(BackEdge);
const SCEV *BEValue = getSCEV(BEValueV);
// NOTE: If BEValue is loop invariant, we know that the PHI node just
@ -2657,8 +2671,7 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
HasNSW = true;
}
const SCEV *StartVal =
getSCEV(PN->getIncomingValue(IncomingEdge));
const SCEV *StartVal = getSCEV(StartValueV);
const SCEV *PHISCEV =
getAddRecExpr(StartVal, Accum, L, HasNUW, HasNSW);
@ -2684,7 +2697,7 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
// Because the other in-value of i (0) fits the evolution of BEValue
// i really is an addrec evolution.
if (AddRec->getLoop() == L && AddRec->isAffine()) {
const SCEV *StartVal = getSCEV(PN->getIncomingValue(IncomingEdge));
const SCEV *StartVal = getSCEV(StartValueV);
// If StartVal = j.start - j.stride, we can use StartVal as the
// initial step of the addrec evolution.
@ -2702,9 +2715,8 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
}
}
}
return SymbolicName;
}
}
// If the PHI has a single incoming value, follow that value, unless the
// PHI's incoming blocks are in a different loop, in which case doing so

29
test/Analysis/ScalarEvolution/unsimplified-loop.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
; This loop has no preheader, multiple backedges, etc., but ScalarEvolution
; should still be able to analyze it.
; CHECK: %i = phi i64 [ 5, %entry ], [ 5, %alt ], [ %i.next, %loop.a ], [ %i.next, %loop.b ]
; CHECK-NEXT: --> {5,+,1}<%loop>
define void @foo(i1 %p, i1 %q, i1 %s, i1 %u) {
entry:
br i1 %p, label %loop, label %alt
alt:
br i1 %s, label %loop, label %exit
loop:
%i = phi i64 [ 5, %entry ], [ 5, %alt ], [ %i.next, %loop.a ], [ %i.next, %loop.b ]
%i.next = add i64 %i, 1
br i1 %q, label %loop.a, label %loop.b
loop.a:
br label %loop
loop.b:
br i1 %u, label %loop, label %exit
exit:
ret void
}