[PATCH] D58435: [SCEV] Ensure that isHighCostExpansion takes into account what is being divided

[Dave Green via Phabricator via llvm-commits]

dmgreen added a comment.

> Is it possible that the tests were checking the correctness for certain expressions that we no longer check because these happen to be expensive?

All the tests in replace-loop-exit-folds.ll are added for this patch. It's showing the changes produced by this patch, but the left hand files are not in-tree yet (it would have been clearer if I would have mentioned that). Most of the tests are a loop like this, with S being signed or unsigned, and with a while or a do loop. They were originally out of D52508 <https://reviews.llvm.org/D52508> (but that doesn't fix most of the cases).

  while(S >= 32) {
      S -= 32;
      something();
  };
  return S;

no-iv-rewrite.ll is returning back to what it was before rL194116 <https://reviews.llvm.org/rL194116>, so is now testing the original point of the test again. The full diff for before and after is much like the other newly added tests (i.e. now a lot smaller):

   define i64 @cloneOr(i32 %limit, i64* %base) #0 {
   entry:
     %halfLim = ashr i32 %limit, 2
     %0 = sext i32 %halfLim to i64
  -  %1 = icmp sgt i32 %halfLim, 2
  -  %smax = select i1 %1, i32 %halfLim, i32 2
  -  %2 = add i32 %smax, -1
  -  %3 = zext i32 %2 to i64
  -  %4 = lshr i64 %3, 1
  -  %5 = shl i64 %4, 1
     br label %loop
  
   loop:                                             ; preds = %loop, %entry
     %indvars.iv = phi i64 [ %indvars.iv.next, %loop ], [ 0, %entry ]
     %adr = getelementptr i64, i64* %base, i64 %indvars.iv
     %val = load i64, i64* %adr
  +  %1 = or i64 %indvars.iv, 1
     %indvars.iv.next = add nuw nsw i64 %indvars.iv, 2
     %cmp = icmp slt i64 %indvars.iv.next, %0
     br i1 %cmp, label %loop, label %exit
  
   exit:                                             ; preds = %loop
     %val.lcssa = phi i64 [ %val, %loop ]
  -  %6 = add i64 %5, 1
  -  %result = and i64 %val.lcssa, %6
  +  %t3.lcssa = phi i64 [ %1, %loop ]
  +  %result = and i64 %val.lcssa, %t3.lcssa
     ret i64 %result
   }


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D58435/new/

https://reviews.llvm.org/D58435