[llvm] b320772 - [NFCI][SCEV] `computeExitLimitFromCondFromBinOp()`: rely on `getSequentialMinMaxExpr()` constant relaxation

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2022-01-14T17:07:48+03:00
New Revision: b32077234b1affbab9a641628c417a9fb1601414

URL: https://github.com/llvm/llvm-project/commit/b32077234b1affbab9a641628c417a9fb1601414
DIFF: https://github.com/llvm/llvm-project/commit/b32077234b1affbab9a641628c417a9fb1601414.diff

LOG: [NFCI][SCEV] `computeExitLimitFromCondFromBinOp()`: rely on `getSequentialMinMaxExpr()` constant relaxation

`getSequentialMinMaxExpr()` has been taught to perform this relaxation,
so rely on that now. Not sure this can be tested.

Added: 
    

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 19eaf174885b..beba8c3a4c01 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8369,26 +8369,11 @@ ScalarEvolution::computeExitLimitFromCondFromBinOp(
   if (EitherMayExit) {
     // Both conditions must be same for the loop to continue executing.
     // Choose the less conservative count.
-    // If ExitCond is a short-circuit form (select), using
-    // umin(EL0.ExactNotTaken, EL1.ExactNotTaken) is unsafe in general.
-    // To see the detailed examples, please see
-    // test/Analysis/ScalarEvolution/exit-count-select.ll
-    bool PoisonSafe = isa<BinaryOperator>(ExitCond);
-    if (!PoisonSafe)
-      // Even if ExitCond is select, we can safely derive BECount using both
-      // EL0 and EL1 in these cases:
-      // (1) EL0.ExactNotTaken is non-zero
-      // (2) EL1.ExactNotTaken is non-poison
-      // (3) EL0.ExactNotTaken is zero (BECount should be simply zero and
-      //     it cannot be umin(0, ..))
-      // The PoisonSafe assignment below is simplified and the assertion after
-      // BECount calculation fully guarantees the condition (3).
-      PoisonSafe = isa<SCEVConstant>(EL0.ExactNotTaken) ||
-                   isa<SCEVConstant>(EL1.ExactNotTaken);
     if (EL0.ExactNotTaken != getCouldNotCompute() &&
         EL1.ExactNotTaken != getCouldNotCompute()) {
-      BECount = getUMinFromMismatchedTypes(EL0.ExactNotTaken, EL1.ExactNotTaken,
-                                           /*Sequential=*/!PoisonSafe);
+      BECount = getUMinFromMismatchedTypes(
+          EL0.ExactNotTaken, EL1.ExactNotTaken,
+          /*Sequential=*/!isa<BinaryOperator>(ExitCond));
 
       // If EL0.ExactNotTaken was zero and ExitCond was a short-circuit form,
       // it should have been simplified to zero (see the condition (3) above)