If the LHS of the comparison is a loop-invariant we also want to move it

to the RHS. This simple change allows to compute loop iteration count 
for loops with condition similar to the one in the testcase (which seems 
to be quite common).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46959 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Wojciech Matyjewicz 2008-02-11 18:37:34 +00:00
parent 1f801fa5ad
commit a089b10421
2 changed files with 17 additions and 2 deletions

View File

@ -1819,8 +1819,8 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
// At this point, we would like to compute how many iterations of the
// loop the predicate will return true for these inputs.
if (isa<SCEVConstant>(LHS) && !isa<SCEVConstant>(RHS)) {
// If there is a constant, force it into the RHS.
if (LHS->isLoopInvariant(L) && !RHS->isLoopInvariant(L)) {
// If there is a loop-invariant, force it into the RHS.
std::swap(LHS, RHS);
Cond = ICmpInst::getSwappedPredicate(Cond);
}

View File

@ -0,0 +1,15 @@
; RUN: llvm-as < %s | opt -scalar-evolution -analyze | not grep Unpredictable
define void @foo(i32 %n) {
entry:
br label %header
header:
%i = phi i32 [ 0, %entry ], [ %i.inc, %next ]
%cond = icmp sgt i32 %n, %i
br i1 %cond, label %next, label %return
next:
%i.inc = add i32 %i, 1
br label %header
return:
ret void
}