Teach SCEV's icmp simplification logic that a-b == 0 is equivalent to a == b.
This also required making recursive simplifications until
nothing changes or a hard limit (currently 3) is hit.
With the simplification in place indvars can canonicalize
loops of the form
for (unsigned i = 0; i < a-b; ++i)
into
for (unsigned i = 0; i != a-b; ++i)
which used to fail because SCEV created a weird umax expr
for the backedge taken count.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157701 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 8781441..c45cc8d 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -5605,9 +5605,14 @@
/// predicate Pred. Return true iff any changes were made.
///
bool ScalarEvolution::SimplifyICmpOperands(ICmpInst::Predicate &Pred,
- const SCEV *&LHS, const SCEV *&RHS) {
+ const SCEV *&LHS, const SCEV *&RHS,
+ unsigned Depth) {
bool Changed = false;
+ // If we hit the max recursion limit bail out.
+ if (Depth >= 3)
+ return false;
+
// Canonicalize a constant to the right side.
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
// Check for both operands constant.
@@ -5645,6 +5650,15 @@
default: llvm_unreachable("Unexpected ICmpInst::Predicate value!");
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE:
+ // Fold ((-1) * %a) + %b == 0 (equivalent to %b-%a == 0) into %a == %b.
+ if (!RA)
+ if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(LHS))
+ if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(AE->getOperand(0)))
+ if (ME->getOperand(0)->isAllOnesValue()) {
+ RHS = AE->getOperand(1);
+ LHS = ME->getOperand(1);
+ Changed = true;
+ }
break;
case ICmpInst::ICMP_UGE:
if ((RA - 1).isMinValue()) {
@@ -5846,6 +5860,11 @@
// TODO: More simplifications are possible here.
+ // Recursively simplify until we either hit a recursion limit or nothing
+ // changes.
+ if (Changed)
+ return SimplifyICmpOperands(Pred, LHS, RHS, Depth+1);
+
return Changed;
trivially_true: