[PATCH] D28393: [SCEV] Make howFarToZero produce a smaller max backedge-taken count

[Sanjoy Das via Phabricator via llvm-commits]

sanjoy accepted this revision.
sanjoy added a comment.
This revision is now accepted and ready to land.

lgtm



================
Comment at: lib/Analysis/ScalarEvolution.cpp:7209
   if (StepC->getValue()->equalsInt(1) || StepC->getValue()->isAllOnesValue()) {
-    ConstantRange CR = getUnsignedRange(Start);
-    const SCEV *MaxBECount;
-    if (!CountDown && CR.getUnsignedMin().isMinValue())
-      // When counting up, the worst starting value is 1, not 0.
-      MaxBECount = CR.getUnsignedMax().isMinValue()
-        ? getConstant(APInt::getMinValue(CR.getBitWidth()))
-        : getConstant(APInt::getMaxValue(CR.getBitWidth()));
-    else
-      MaxBECount = getConstant(CountDown ? CR.getUnsignedMax()
-                                         : -CR.getUnsignedMin());
-    return ExitLimit(Distance, MaxBECount, false, Predicates);
+    APInt MaxBECount = getUnsignedRange(Distance).getUnsignedMax();
+    return ExitLimit(Distance, getConstant(MaxBECount), false, Predicates);
----------------
I'd add a one-liner here:

```
// Solve {Distance,+,-1} == 0.
```



Repository:
  rL LLVM

https://reviews.llvm.org/D28393