variable (with step 1) and m is its final value. Then, the correct trip
count is SMAX(m,n)-n. Previously, we used SMAX(0,m-n), but m-n may
overflow and can't in general be interpreted as signed.
Patch by Nick Lewycky.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47007
91177308-0d34-0410-b5e6-
96231b3b80d8
if (AddRec->isAffine()) {
// The number of iterations for "{n,+,1} < m", is m-n. However, we don't
// know that m is >= n on input to the loop. If it is, the condition
if (AddRec->isAffine()) {
// The number of iterations for "{n,+,1} < m", is m-n. However, we don't
// know that m is >= n on input to the loop. If it is, the condition
- // returns true zero times. To handle both cases, we return SMAX(0, m-n).
+ // returns true zero times. To handle both cases, we return SMAX(m, n)-n.
// FORNOW: We only support unit strides.
SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
if (AddRec->getOperand(1) != One)
return UnknownValue;
// FORNOW: We only support unit strides.
SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
if (AddRec->getOperand(1) != One)
return UnknownValue;
- SCEVHandle Iters = SE.getMinusSCEV(RHS, AddRec->getOperand(0));
+ SCEVHandle Start = AddRec->getOperand(0);
+ SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS, Start) : (SCEVHandle)RHS;
- if (isSigned)
- return SE.getSMaxExpr(SE.getIntegerSCEV(0, RHS->getType()), Iters);
- else
- return Iters;
+ return SE.getMinusSCEV(End, Start);
--- /dev/null
+; RUN: llvm-as < %s | opt -scalar-evolution -analyze | grep {Loop loop: ( 100 + ( -100 smax %n)) iterations!}
+; PR2002
+
+define void @foo(i8 %n) {
+entry:
+ br label %loop
+loop:
+ %i = phi i8 [ -100, %entry ], [ %i.inc, %next ]
+ %cond = icmp slt i8 %i, %n
+ br i1 %cond, label %next, label %return
+next:
+ %i.inc = add i8 %i, 1
+ br label %loop
+return:
+ ret void
+}