Step #2 to improve trip count analysis for loops like this:

void f(int* begin, int* end) { std::fill(begin, end, 0); }

which turns into a != exit expression where one pointer is
strided and (thanks to step #1) known to not overflow, and 
the other is loop invariant.

The observation here is that, though the IV is strided by
4 in this case, that the IV *has* to become equal to the
end value.  It cannot "miss" the end value by stepping over
it, because if it did, the strided IV expression would
eventually wrap around.

Handle this by turning A != B into "A-B != 0" where the A-B
part is known to be NUW.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123131 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 1 deletions

diff --git a/include/llvm/Analysis/ScalarEvolution.h b/include/llvm/Analysis/ScalarEvolution.h
index d910406..4706c09 100644
--- a/include/llvm/Analysis/ScalarEvolution.h
+++ b/include/llvm/Analysis/ScalarEvolution.h
@@ -539,7 +539,8 @@ namespace llvm {
 
     /// getMinusSCEV - Return LHS-RHS.
     ///
-    const SCEV *getMinusSCEV(const SCEV *LHS, const SCEV *RHS);
+    const SCEV *getMinusSCEV(const SCEV *LHS, const SCEV *RHS,
+                             bool HasNUW = false, bool HasNSW = false);
 
     /// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion
     /// of the input value to the specified type.  If the type must be