[IndVarSimplify] Use control-dependent range information to prove non-negativity

    
This change is motivated by the case when IndVarSimplify doesn't widen a comparison of IV increment because it can't prove IV increment being non-negative. We end up with a redundant trunc of the widened increment on this example.

for.body:
  %i = phi i32 [ %start, %for.body.lr.ph ], [ %i.inc, %for.inc ]
  %within_limits = icmp ult i32 %i, 64
  br i1 %within_limits, label %continue, label %for.end

continue:
  %i.i64 = zext i32 %i to i64
  %arrayidx = getelementptr inbounds i32, i32* %base, i64 %i.i64
  %val = load i32, i32* %arrayidx, align 4
  br label %for.inc

for.inc:
  %i.inc = add nsw nuw i32 %i, 1
  %cmp = icmp slt i32 %i.inc, %limit
  br i1 %cmp, label %for.body, label %for.end

There is a range check inside of the loop which guarantees the IV to be non-negative. NSW on the increment guarantees that the increment is also non-negative. Teach IndVarSimplify to use the range check to prove non-negativity of loop increments.

Reviewed By: sanjoy

Differential Revision: https://reviews.llvm.org/D25738

llvm-svn: 284629

0 files changed, 0 insertions, 0 deletions