[llvm] 2800058 - [SCEV] Revert two speculative compile time optimizations which made no difference

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-11-19T08:45:56-08:00
New Revision: 28000587e1a4133d00186825d3e346af27ed39ad

URL: https://github.com/llvm/llvm-project/commit/28000587e1a4133d00186825d3e346af27ed39ad
DIFF: https://github.com/llvm/llvm-project/commit/28000587e1a4133d00186825d3e346af27ed39ad.diff

LOG: [SCEV] Revert two speculative compile time optimizations which made no difference

Revert "[SCEV] Defer all work from ea12c2cb as late as possible"
Revert "[SCEV] Defer loop property checks from ea12c2cb as late as possible"

This reverts commit 734abbad79dbcbd0e880510fbab1ef0e701cfc7b and  1a5666acb281c7510504e726ba481d09ab5f5b95.

Both of these changes were speculative attempts to address a compile time regression.  Neither worked, and both complicated the code in undesirable ways.

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 40bd1b593560e..f7c22cfb03100 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8321,14 +8321,8 @@ 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) {
-    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 isLoopInvariant(RHS, L) && loopHasNoAbnormalExits(L) &&
-        loopIsFiniteByAssumption(L);
-    };
+  if (ControlsExit && isLoopInvariant(RHS, L) && 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.
@@ -8336,16 +8330,14 @@ ScalarEvolution::computeExitLimitFromICmp(const Loop *L,
     if (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(LHS))
       InnerLHS = ZExt->getOperand();
     if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(InnerLHS)) {
-      if (!AR->hasNoSelfWrap() && AR->getLoop() == L && AR->isAffine()) {
-        auto *StrideC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this));
-        if (StrideC && StrideC->getAPInt().isPowerOf2() &&
-            deferredLoopProperties()) {
-          auto Flags = AR->getNoWrapFlags();
-          Flags = setFlags(Flags, SCEV::FlagNW);
-          SmallVector<const SCEV*> Operands{AR->operands()};
-          Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
-          setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
-        }
+      auto *StrideC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this));
+      if (!AR->hasNoSelfWrap() && AR->getLoop() == L && AR->isAffine() && 
+          StrideC && StrideC->getAPInt().isPowerOf2()) {
+        auto Flags = AR->getNoWrapFlags();
+        Flags = setFlags(Flags, SCEV::FlagNW);
+        SmallVector<const SCEV*> Operands{AR->operands()};
+        Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
+        setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
       }
     }
   }