From adae053b5365b6a7f92682e306c410f2e129a24d Mon Sep 17 00:00:00 2001 From: Wojciech Matyjewicz Date: Mon, 11 Feb 2008 18:37:34 +0000 Subject: [PATCH] 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). llvm-svn: 46959 --- llvm/lib/Analysis/ScalarEvolution.cpp | 4 ++-- .../2008-02-11-ReversedCondition.ll | 15 +++++++++++++++ 2 files changed, 17 insertions(+), 2 deletions(-) create mode 100644 llvm/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp index cbfc56373aea..122dba3e6ac0 100644 --- a/llvm/lib/Analysis/ScalarEvolution.cpp +++ b/llvm/lib/Analysis/ScalarEvolution.cpp @@ -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(LHS) && !isa(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); } diff --git a/llvm/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll b/llvm/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll new file mode 100644 index 000000000000..3cdb1e3c768f --- /dev/null +++ b/llvm/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll @@ -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 +}