[llvm] 44d70d2 - [LoopUnroll] Eliminate PreserveOnlyFirst parameter [nfc]

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-06-03T10:33:14-07:00
New Revision: 44d70d298acc872f37819efcb101334674a289e9

URL: https://github.com/llvm/llvm-project/commit/44d70d298acc872f37819efcb101334674a289e9
DIFF: https://github.com/llvm/llvm-project/commit/44d70d298acc872f37819efcb101334674a289e9.diff

LOG: [LoopUnroll] Eliminate PreserveOnlyFirst parameter [nfc]

This is a first step towards simplifying the transform interface to be less error prone. The basic idea is that querying SCEV is cheap (since it's cached) and we can just check for properties related to branch folding in the transform method instead of relying on the heuristic part to pass everything in correctly.

Differential Revision: https://reviews.llvm.org/D103584

Added: 
    

Modified: 
    llvm/include/llvm/Transforms/Utils/UnrollLoop.h
    llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
    llvm/lib/Transforms/Utils/LoopUnroll.cpp
    llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Transforms/Utils/UnrollLoop.h b/llvm/include/llvm/Transforms/Utils/UnrollLoop.h
index 4254bd71a41c0..11e5b3b41eb65 100644
--- a/llvm/include/llvm/Transforms/Utils/UnrollLoop.h
+++ b/llvm/include/llvm/Transforms/Utils/UnrollLoop.h
@@ -71,7 +71,6 @@ struct UnrollLoopOptions {
   bool AllowRuntime;
   bool AllowExpensiveTripCount;
   bool PreserveCondBr;
-  bool PreserveOnlyFirst;
   unsigned TripMultiple;
   unsigned PeelCount;
   bool UnrollRemainder;

diff  --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 71a2b89decf74..6ee0ce78cb480 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -1166,7 +1166,7 @@ static LoopUnrollResult tryToUnrollLoop(
   LoopUnrollResult UnrollResult = UnrollLoop(
       L,
       {UP.Count, TripCount, UP.Force, UP.Runtime, UP.AllowExpensiveTripCount,
-       UseUpperBound, MaxOrZero, TripMultiple, PP.PeelCount, UP.UnrollRemainder,
+       UseUpperBound, TripMultiple, PP.PeelCount, UP.UnrollRemainder,
        ForgetAllSCEV},
       LI, &SE, &DT, &AC, &TTI, &ORE, PreserveLCSSA, &RemainderLoop);
   if (UnrollResult == LoopUnrollResult::Unmodified)

diff  --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 3fdcd0d08e91b..5f7395d4cbec7 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -256,8 +256,7 @@ void llvm::simplifyLoopAfterUnroll(Loop *L, bool SimplifyIVs, LoopInfo *LI,
 ///
 /// PreserveCondBr indicates whether the conditional branch of the LatchBlock
 /// needs to be preserved.  It is needed when we use trip count upper bound to
-/// fully unroll the loop. If PreserveOnlyFirst is also set then only the first
-/// conditional branch needs to be preserved.
+/// fully unroll the loop.
 ///
 /// Similarly, TripMultiple divides the number of times that the LatchBlock may
 /// execute without exiting the loop.
@@ -381,6 +380,11 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
       any_of(ExitBlocks,
              [](const BasicBlock *BB) { return isa<PHINode>(BB->begin()); });
 
+  const unsigned MaxTripCount = SE->getSmallConstantMaxTripCount(L);
+  const bool MaxOrZero = SE->isBackedgeTakenCountMaxOrZero(L);
+
+  const bool PreserveOnlyFirst = ULO.Count == MaxTripCount && MaxOrZero;
+
   // The current loop unroll pass can unroll loops that have
   // (1) single latch; and
   // (2a) latch is unconditional; or
@@ -755,7 +759,7 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
 
     auto WillExit = [&](unsigned i, unsigned j) -> Optional<bool> {
       if (CompletelyUnroll) {
-        if (ULO.PreserveCondBr && j && !(ULO.PreserveOnlyFirst && i != 0))
+        if (ULO.PreserveCondBr && j && !(PreserveOnlyFirst && i != 0))
           return None;
         return j == 0;
       }

diff  --git a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
index 5105c53e74bd6..cc85fb68df1f2 100644
--- a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -987,7 +987,7 @@ bool llvm::UnrollRuntimeLoopRemainder(
                    {/*Count*/ Count - 1, /*TripCount*/ Count - 1,
                     /*Force*/ false, /*AllowRuntime*/ false,
                     /*AllowExpensiveTripCount*/ false, /*PreserveCondBr*/ true,
-                    /*PreserveOnlyFirst*/ false, /*TripMultiple*/ 1,
+                    /*TripMultiple*/ 1,
                     /*PeelCount*/ 0, /*UnrollRemainder*/ false, ForgetAllSCEV},
                    LI, SE, DT, AC, TTI, /*ORE*/ nullptr, PreserveLCSSA);
   }