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Fix ScalarEvolution's "exhaustive" trip count evaluation code to avoid

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assuming that loops are in canonical form, as ScalarEvolution doesn't
depend on LoopSimplify itself. Also, with indirectbr not all loops can
be simplified. This fixes PR7416.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106389 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-06-19 14:17:24 +00:00
parent 485c43fc47
commit b92654d9c9
2 changed files with 36 additions and 2 deletions
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7
lib/Analysis/ScalarEvolution.cpp
View File

@ -4238,8 +4238,11 @@ ScalarEvolution::ComputeBackedgeTakenCountExhaustively(const Loop *L,
PHINode *PN = getConstantEvolvingPHI(Cond, L);
if (PN == 0) return getCouldNotCompute();
// Since the loop is canonicalized, the PHI node must have two entries. One
// entry must be a constant (coming in from outside of the loop), and the
// If the loop is canonicalized, the PHI will have exactly two entries.
// That's the only form we support here.
if (PN->getNumIncomingValues() != 2) return getCouldNotCompute();
// One entry must be a constant (coming in from outside of the loop), and the
// second must be derived from the same PHI.
bool SecondIsBackedge = L->contains(PN->getIncomingBlock(1));
Constant *StartCST =

31
test/Analysis/ScalarEvolution/trip-count10.ll
View File

@ -74,3 +74,34 @@ loop:
return:
ret void
}
; Trip counts for non-polynomial iterations. It's theoretically possible
; to compute a maximum count for these, but short of that, ScalarEvolution
; should return unknown.
; PR7416
; CHECK: Determining loop execution counts for: @nonpolynomial
; CHECK-NEXT: Loop %loophead: Unpredictable backedge-taken count
; CHECK-NEXT: Loop %loophead: Unpredictable max backedge-taken count
declare i1 @g() nounwind
define void @nonpolynomial() {
entry:
br label %loophead
loophead:
%x = phi i32 [0, %entry], [%x.1, %bb1], [%x.2, %bb2]
%y = icmp slt i32 %x, 100
br i1 %y, label %loopbody, label %retbb
loopbody:
%z = call i1 @g()
br i1 %z, label %bb1, label %bb2
bb1:
%x.1 = add i32 %x, 2
br label %loophead
bb2:
%x.2 = add i32 %x, 3
br label %loophead
retbb:
ret void
}