[llvm] 1a5666a - [SCEV] Defer loop property checks from ea12c2cb as late as possible

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-11-18T13:47:45-08:00
New Revision: 1a5666acb281c7510504e726ba481d09ab5f5b95

URL: https://github.com/llvm/llvm-project/commit/1a5666acb281c7510504e726ba481d09ab5f5b95
DIFF: https://github.com/llvm/llvm-project/commit/1a5666acb281c7510504e726ba481d09ab5f5b95.diff

LOG: [SCEV] Defer loop property checks from ea12c2cb as late as possible

This is a speculative compile time optimization to address a reported regression.  It's the only thing which vaguely makes sense.

Added: 
    

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp

Removed: 
    


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diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index f7c22cfb03100..adc4540bb2b7d 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8321,8 +8321,13 @@ ScalarEvolution::computeExitLimitFromICmp(const Loop *L,
   // the same values on self-wrap of the IV, then we can infer that IV
   // doesn't self wrap because if it did, we'd have an infinite (undefined)
   // loop.
-  if (ControlsExit && isLoopInvariant(RHS, L) && loopHasNoAbnormalExits(L) &&
-      loopIsFiniteByAssumption(L)) {
+  if (ControlsExit && isLoopInvariant(RHS, L)) {
+    auto deferredLoopProperties = [&]() {
+      // Conceptually, these two checks should be in the immediately guarding
+      // if clause, but we defer their actual execution to after the cheaper
+      // checks have all been done.
+      return loopHasNoAbnormalExits(L) && loopIsFiniteByAssumption(L);
+    };
 
     // TODO: We can peel off any functions which are invertible *in L*.  Loop
     // invariant terms are effectively constants for our purposes here.
@@ -8332,7 +8337,8 @@ ScalarEvolution::computeExitLimitFromICmp(const Loop *L,
     if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(InnerLHS)) {
       auto *StrideC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this));
       if (!AR->hasNoSelfWrap() && AR->getLoop() == L && AR->isAffine() && 
-          StrideC && StrideC->getAPInt().isPowerOf2()) {
+          StrideC && StrideC->getAPInt().isPowerOf2() &&
+          deferredLoopProperties()) {
         auto Flags = AR->getNoWrapFlags();
         Flags = setFlags(Flags, SCEV::FlagNW);
         SmallVector<const SCEV*> Operands{AR->operands()};