Revert "Re-enable "[IRCE] Identify loops with latch comparison against current IV value""

Revert the patch causing the functional failures.
The patch owner is notified with test cases which fail.
Test case has been provided to Maxim offline.

llvm-svn: 313857

2 files changed, 13 insertions, 296 deletions

diff --git a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index e625fb463dc..9fa49fdf81f 100644
--- a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -450,20 +450,10 @@ struct LoopStructure {
   // equivalent to:
   //
   // intN_ty inc = IndVarIncreasing ? 1 : -1;
-  // pred_ty predicate = IndVarIncreasing
-  //                         ? IsSignedPredicate ? ICMP_SLT : ICMP_ULT
-  //                         : IsSignedPredicate ? ICMP_SGT : ICMP_UGT;
+  // pred_ty predicate = IndVarIncreasing ? ICMP_SLT : ICMP_SGT;
   //
-  //
-  // for (intN_ty iv = IndVarStart; predicate(IndVarBase, LoopExitAt);
-  //      iv = IndVarNext)
+  // for (intN_ty iv = IndVarStart; predicate(iv, LoopExitAt); iv = IndVarBase)
   //   ... body ...
-  //
-  // Here IndVarBase is either current or next value of the induction variable.
-  // in the former case, IsIndVarNext = false and IndVarBase points to the
-  // Phi node of the induction variable. Otherwise, IsIndVarNext = true and
-  // IndVarBase points to IV increment instruction.
-  //
 
   Value *IndVarBase;
   Value *IndVarStart;
@@ -471,13 +461,12 @@ struct LoopStructure {
   Value *LoopExitAt;
   bool IndVarIncreasing;
   bool IsSignedPredicate;
-  bool IsIndVarNext;
 
   LoopStructure()
       : Tag(""), Header(nullptr), Latch(nullptr), LatchBr(nullptr),
         LatchExit(nullptr), LatchBrExitIdx(-1), IndVarBase(nullptr),
         IndVarStart(nullptr), IndVarStep(nullptr), LoopExitAt(nullptr),
-        IndVarIncreasing(false), IsSignedPredicate(true), IsIndVarNext(false) {}
+        IndVarIncreasing(false), IsSignedPredicate(true) {}
 
   template <typename M> LoopStructure map(M Map) const {
     LoopStructure Result;
@@ -493,7 +482,6 @@ struct LoopStructure {
     Result.LoopExitAt = Map(LoopExitAt);
     Result.IndVarIncreasing = IndVarIncreasing;
     Result.IsSignedPredicate = IsSignedPredicate;
-    Result.IsIndVarNext = IsIndVarNext;
     return Result;
   }
 
@@ -841,42 +829,21 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
     return false;
   };
 
-  // `ICI` can either be a comparison against IV or a comparison of IV.next.
-  // Depending on the interpretation, we calculate the start value differently.
+  // `ICI` is interpreted as taking the backedge if the *next* value of the
+  // induction variable satisfies some constraint.
 
-  // Pair {IndVarBase; IsIndVarNext} semantically designates whether the latch
-  // comparisons happens against the IV before or after its value is
-  // incremented. Two valid combinations for them are:
-  //
-  // 1) { phi [ iv.start, preheader ], [ iv.next, latch ]; false },
-  // 2) { iv.next; true }.
-  //
-  // The latch comparison happens against IndVarBase which can be either current
-  // or next value of the induction variable.
   const SCEVAddRecExpr *IndVarBase = cast<SCEVAddRecExpr>(LeftSCEV);
   bool IsIncreasing = false;
   bool IsSignedPredicate = true;
-  bool IsIndVarNext = false;
   ConstantInt *StepCI;
   if (!IsInductionVar(IndVarBase, IsIncreasing, StepCI)) {
     FailureReason = "LHS in icmp not induction variable";
     return None;
   }
 
-  const SCEV *IndVarStart = nullptr;
-  // TODO: Currently we only handle comparison against IV, but we can extend
-  // this analysis to be able to deal with comparison against sext(iv) and such.
-  if (isa<PHINode>(LeftValue) &&
-      cast<PHINode>(LeftValue)->getParent() == Header)
-    // The comparison is made against current IV value.
-    IndVarStart = IndVarBase->getStart();
-  else {
-    // Assume that the comparison is made against next IV value.
-    const SCEV *StartNext = IndVarBase->getStart();
-    const SCEV *Addend = SE.getNegativeSCEV(IndVarBase->getStepRecurrence(SE));
-    IndVarStart = SE.getAddExpr(StartNext, Addend);
-    IsIndVarNext = true;
-  }
+  const SCEV *StartNext = IndVarBase->getStart();
+  const SCEV *Addend = SE.getNegativeSCEV(IndVarBase->getStepRecurrence(SE));
+  const SCEV *IndVarStart = SE.getAddExpr(StartNext, Addend);
   const SCEV *Step = SE.getSCEV(StepCI);
 
   ConstantInt *One = ConstantInt::get(IndVarTy, 1);
@@ -1060,7 +1027,6 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
   Result.IndVarIncreasing = IsIncreasing;
   Result.LoopExitAt = RightValue;
   Result.IsSignedPredicate = IsSignedPredicate;
-  Result.IsIndVarNext = IsIndVarNext;
 
   FailureReason = nullptr;
 
@@ -1350,8 +1316,8 @@ LoopConstrainer::RewrittenRangeInfo LoopConstrainer::changeIterationSpaceEnd(
                                       BranchToContinuation);
 
     NewPHI->addIncoming(PN->getIncomingValueForBlock(Preheader), Preheader);
-    auto *FixupValue = PN->getIncomingValueForBlock(LS.Latch);
-    NewPHI->addIncoming(FixupValue, RRI.ExitSelector);
+    NewPHI->addIncoming(PN->getIncomingValueForBlock(LS.Latch),
+                        RRI.ExitSelector);
     RRI.PHIValuesAtPseudoExit.push_back(NewPHI);
   }
 
@@ -1492,6 +1458,7 @@ bool LoopConstrainer::run() {
       }
       ExitPreLoopAtSCEV = SE.getAddExpr(*SR.HighLimit, MinusOneS);
     }
+
     ExitPreLoopAt = Expander.expandCodeFor(ExitPreLoopAtSCEV, IVTy, InsertPt);
     ExitPreLoopAt->setName("exit.preloop.at");
   }
@@ -1510,9 +1477,7 @@ bool LoopConstrainer::run() {
       }
       ExitMainLoopAtSCEV = SE.getAddExpr(*SR.LowLimit, MinusOneS);
     }
-    if (!MainLoopStructure.IsIndVarNext)
-      ExitMainLoopAtSCEV = SE.getMinusSCEV(
-          ExitMainLoopAtSCEV, SE.getSCEV(MainLoopStructure.IndVarStep));
+
     ExitMainLoopAt = Expander.expandCodeFor(ExitMainLoopAtSCEV, IVTy, InsertPt);
     ExitMainLoopAt->setName("exit.mainloop.at");
   }
@@ -1735,10 +1700,7 @@ bool InductiveRangeCheckElimination::runOnLoop(Loop *L, LPPassManager &LPM) {
   }
   LoopStructure LS = MaybeLoopStructure.getValue();
   const SCEVAddRecExpr *IndVar =
-      cast<SCEVAddRecExpr>(SE.getSCEV(LS.IndVarBase));
-  if (LS.IsIndVarNext)
-    IndVar = cast<SCEVAddRecExpr>(SE.getMinusSCEV(IndVar,
-                                                  SE.getSCEV(LS.IndVarStep)));
+      cast<SCEVAddRecExpr>(SE.getMinusSCEV(SE.getSCEV(LS.IndVarBase), SE.getSCEV(LS.IndVarStep)));
 
   Optional<InductiveRangeCheck::Range> SafeIterRange;
   Instruction *ExprInsertPt = Preheader->getTerminator();
diff --git a/llvm/test/Transforms/IRCE/latch-comparison-against-current-value.ll b/llvm/test/Transforms/IRCE/latch-comparison-against-current-value.ll
deleted file mode 100644
index 8ad4e3d3967..00000000000
--- a/llvm/test/Transforms/IRCE/latch-comparison-against-current-value.ll
+++ /dev/null
@@ -1,245 +0,0 @@
-; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -S < %s 2>&1 | FileCheck %s
-
-; Check that IRCE is able to deal with loops where the latch comparison is
-; done against current value of the IV, not the IV.next.
-
-; CHECK: irce: in function test_01: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
-; CHECK: irce: in function test_02: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
-; CHECK-NOT: irce: in function test_03: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
-; CHECK-NOT: irce: in function test_04: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
-; CHECK: irce: in function test_05: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
-
-; SLT condition for increasing loop from 0 to 100.
-define void @test_01(i32* %arr, i32* %a_len_ptr) #0 {
-
-; CHECK:      test_01
-; CHECK:        entry:
-; CHECK-NEXT:     %len = load i32, i32* %a_len_ptr, !range !0
-; CHECK-NEXT:     %exit.mainloop.at = add i32 %len, -1
-; CHECK-NEXT:     [[COND2:%[^ ]+]] = icmp slt i32 0, %exit.mainloop.at
-; CHECK-NEXT:     br i1 [[COND2]], label %loop.preheader, label %main.pseudo.exit
-; CHECK:        loop:
-; CHECK-NEXT:     %idx = phi i32 [ %idx.next, %in.bounds ], [ 0, %loop.preheader ]
-; CHECK-NEXT:     %idx.next = add nuw nsw i32 %idx, 1
-; CHECK-NEXT:     %abc = icmp slt i32 %idx, %len
-; CHECK-NEXT:     br i1 true, label %in.bounds, label %out.of.bounds.loopexit1
-; CHECK:        in.bounds:
-; CHECK-NEXT:     %addr = getelementptr i32, i32* %arr, i32 %idx
-; CHECK-NEXT:     store i32 0, i32* %addr
-; CHECK-NEXT:     %next = icmp slt i32 %idx, 100
-; CHECK-NEXT:     [[COND3:%[^ ]+]] = icmp slt i32 %idx, %exit.mainloop.at
-; CHECK-NEXT:     br i1 [[COND3]], label %loop, label %main.exit.selector
-; CHECK:        main.exit.selector:
-; CHECK-NEXT:     %idx.lcssa = phi i32 [ %idx, %in.bounds ]
-; CHECK-NEXT:     %idx.next.lcssa = phi i32 [ %idx.next, %in.bounds ]
-; CHECK-NEXT:     [[COND4:%[^ ]+]] = icmp slt i32 %idx.lcssa, 100
-; CHECK-NEXT:     br i1 [[COND4]], label %main.pseudo.exit, label %exit
-; CHECK-NOT: loop.preloop:
-; CHECK:        loop.postloop:
-; CHECK-NEXT:    %idx.postloop = phi i32 [ %idx.copy, %postloop ], [ %idx.next.postloop, %in.bounds.postloop ]
-; CHECK-NEXT:     %idx.next.postloop = add nuw nsw i32 %idx.postloop, 1
-; CHECK-NEXT:     %abc.postloop = icmp slt i32 %idx.postloop, %len
-; CHECK-NEXT:     br i1 %abc.postloop, label %in.bounds.postloop, label %out.of.bounds.loopexit
-
-entry:
-  %len = load i32, i32* %a_len_ptr, !range !0
-  br label %loop
-
-loop:
-  %idx = phi i32 [ 0, %entry ], [ %idx.next, %in.bounds ]
-  %idx.next = add nsw nuw i32 %idx, 1
-  %abc = icmp slt i32 %idx, %len
-  br i1 %abc, label %in.bounds, label %out.of.bounds
-
-in.bounds:
-  %addr = getelementptr i32, i32* %arr, i32 %idx
-  store i32 0, i32* %addr
-  %next = icmp slt i32 %idx, 100
-  br i1 %next, label %loop, label %exit
-
-out.of.bounds:
-  ret void
-
-exit:
-  ret void
-}
-
-; ULT condition for increasing loop from 0 to 100.
-define void @test_02(i32* %arr, i32* %a_len_ptr) #0 {
-
-; CHECK:      test_02
-; CHECK:        entry:
-; CHECK-NEXT:     %len = load i32, i32* %a_len_ptr, !range !0
-; CHECK-NEXT:     %exit.mainloop.at = add i32 %len, -1
-; CHECK-NEXT:     [[COND2:%[^ ]+]] = icmp ult i32 0, %exit.mainloop.at
-; CHECK-NEXT:     br i1 [[COND2]], label %loop.preheader, label %main.pseudo.exit
-; CHECK:        loop:
-; CHECK-NEXT:     %idx = phi i32 [ %idx.next, %in.bounds ], [ 0, %loop.preheader ]
-; CHECK-NEXT:     %idx.next = add nuw nsw i32 %idx, 1
-; CHECK-NEXT:     %abc = icmp ult i32 %idx, %len
-; CHECK-NEXT:     br i1 true, label %in.bounds, label %out.of.bounds.loopexit1
-; CHECK:        in.bounds:
-; CHECK-NEXT:     %addr = getelementptr i32, i32* %arr, i32 %idx
-; CHECK-NEXT:     store i32 0, i32* %addr
-; CHECK-NEXT:     %next = icmp ult i32 %idx, 100
-; CHECK-NEXT:     [[COND3:%[^ ]+]] = icmp ult i32 %idx, %exit.mainloop.at
-; CHECK-NEXT:     br i1 [[COND3]], label %loop, label %main.exit.selector
-; CHECK:        main.exit.selector:
-; CHECK-NEXT:     %idx.lcssa = phi i32 [ %idx, %in.bounds ]
-; CHECK-NEXT:     %idx.next.lcssa = phi i32 [ %idx.next, %in.bounds ]
-; CHECK-NEXT:     [[COND4:%[^ ]+]] = icmp ult i32 %idx.lcssa, 100
-; CHECK-NEXT:     br i1 [[COND4]], label %main.pseudo.exit, label %exit
-; CHECK-NOT: loop.preloop:
-; CHECK:        loop.postloop:
-; CHECK-NEXT:    %idx.postloop = phi i32 [ %idx.copy, %postloop ], [ %idx.next.postloop, %in.bounds.postloop ]
-; CHECK-NEXT:     %idx.next.postloop = add nuw nsw i32 %idx.postloop, 1
-; CHECK-NEXT:     %abc.postloop = icmp ult i32 %idx.postloop, %len
-; CHECK-NEXT:     br i1 %abc.postloop, label %in.bounds.postloop, label %out.of.bounds.loopexit
-
-entry:
-  %len = load i32, i32* %a_len_ptr, !range !0
-  br label %loop
-
-loop:
-  %idx = phi i32 [ 0, %entry ], [ %idx.next, %in.bounds ]
-  %idx.next = add nsw nuw i32 %idx, 1
-  %abc = icmp ult i32 %idx, %len
-  br i1 %abc, label %in.bounds, label %out.of.bounds
-
-in.bounds:
-  %addr = getelementptr i32, i32* %arr, i32 %idx
-  store i32 0, i32* %addr
-  %next = icmp ult i32 %idx, 100
-  br i1 %next, label %loop, label %exit
-
-out.of.bounds:
-  ret void
-
-exit:
-  ret void
-}
-
-; Same as test_01, but comparison happens against IV extended to a wider type.
-; This test ensures that IRCE rejects it and does not falsely assume that it was
-; a comparison against iv.next.
-; TODO: We can actually extend the recognition to cover this case.
-define void @test_03(i32* %arr, i64* %a_len_ptr) #0 {
-
-; CHECK:      test_03
-
-entry:
-  %len = load i64, i64* %a_len_ptr, !range !1
-  br label %loop
-
-loop:
-  %idx = phi i32 [ 0, %entry ], [ %idx.next, %in.bounds ]
-  %idx.next = add nsw nuw i32 %idx, 1
-  %idx.ext = sext i32 %idx to i64
-  %abc = icmp slt i64 %idx.ext, %len
-  br i1 %abc, label %in.bounds, label %out.of.bounds
-
-in.bounds:
-  %addr = getelementptr i32, i32* %arr, i32 %idx
-  store i32 0, i32* %addr
-  %next = icmp slt i32 %idx, 100
-  br i1 %next, label %loop, label %exit
-
-out.of.bounds:
-  ret void
-
-exit:
-  ret void
-}
-
-; Same as test_02, but comparison happens against IV extended to a wider type.
-; This test ensures that IRCE rejects it and does not falsely assume that it was
-; a comparison against iv.next.
-; TODO: We can actually extend the recognition to cover this case.
-define void @test_04(i32* %arr, i64* %a_len_ptr) #0 {
-
-; CHECK:      test_04
-
-entry:
-  %len = load i64, i64* %a_len_ptr, !range !1
-  br label %loop
-
-loop:
-  %idx = phi i32 [ 0, %entry ], [ %idx.next, %in.bounds ]
-  %idx.next = add nsw nuw i32 %idx, 1
-  %idx.ext = sext i32 %idx to i64
-  %abc = icmp ult i64 %idx.ext, %len
-  br i1 %abc, label %in.bounds, label %out.of.bounds
-
-in.bounds:
-  %addr = getelementptr i32, i32* %arr, i32 %idx
-  store i32 0, i32* %addr
-  %next = icmp ult i32 %idx, 100
-  br i1 %next, label %loop, label %exit
-
-out.of.bounds:
-  ret void
-
-exit:
-  ret void
-}
-
-define void @test_05(i32* %arr, i32* %a_len_ptr) #0 {
-
-; CHECK:      test_05
-; CHECK:      entry:
-; CHECK-NEXT:     %len = load i32, i32* %a_len_ptr, !range !0
-; CHECK-NEXT:     %exit.mainloop.at = add i32 %len, -1
-; CHECK-NEXT:     br i1 true, label %loop.preloop.preheader, label %preloop.pseudo.exit
-; CHECK:      loop.preloop:
-; CHECK-NEXT:     %idx.preloop = phi i32 [ %idx.next.preloop, %in.bounds.preloop ], [ -10, %loop.preloop.preheader ]
-; CHECK-NEXT:     %idx.next.preloop = add i32 %idx.preloop, 1
-; CHECK-NEXT:     %c1.preloop = icmp sge i32 %idx.preloop, 0
-; CHECK-NEXT:     %c2.preloop = icmp slt i32 %idx.preloop, %len
-; CHECK-NEXT:     %abc.preloop = and i1 %c1.preloop, %c2.preloop
-; CHECK-NEXT:     br i1 %abc.preloop, label %in.bounds.preloop, label %out.of.bounds.loopexit
-; CHECK:      in.bounds.preloop:
-; CHECK-NEXT:     %addr.preloop = getelementptr i32, i32* %arr, i32 %idx.preloop
-; CHECK-NEXT:     store i32 0, i32* %addr.preloop
-; CHECK-NEXT:     %next.preloop = icmp slt i32 %idx.preloop, 100
-; CHECK-NEXT:     [[COND3:%[^ ]+]] = icmp slt i32 %idx.preloop, 0
-; CHECK-NEXT:     br i1 [[COND3]], label %loop.preloop, label %preloop.exit.selector
-; CHECK:      loop.postloop:
-; CHECK-NEXT:     %idx.postloop = phi i32 [ %idx.copy, %postloop ], [ %idx.next.postloop, %in.bounds.postloop ]
-; CHECK-NEXT:     %idx.next.postloop = add i32 %idx.postloop, 1
-; CHECK-NEXT:     %c1.postloop = icmp sge i32 %idx.postloop, 0
-; CHECK-NEXT:     %c2.postloop = icmp slt i32 %idx.postloop, %len
-; CHECK-NEXT:     %abc.postloop = and i1 %c1.postloop, %c2.postloop
-; CHECK-NEXT:     br i1 %abc.postloop, label %in.bounds.postloop, label %out.of.bounds.loopexit2
-; CHECK:      in.bounds.postloop:
-; CHECK-NEXT:     %addr.postloop = getelementptr i32, i32* %arr, i32 %idx.postloop
-; CHECK-NEXT:     store i32 0, i32* %addr.postloop
-; CHECK-NEXT:     %next.postloop = icmp slt i32 %idx.postloop, 100
-; CHECK-NEXT:     br i1 %next.postloop, label %loop.postloop, label %exit.loopexit
-
-entry:
-  %len = load i32, i32* %a_len_ptr, !range !0
-  br label %loop
-
-loop:
-  %idx = phi i32 [-10, %entry ], [ %idx.next, %in.bounds ]
-  %idx.next = add i32 %idx, 1
-  %c1 = icmp sge i32 %idx, 0
-  %c2 = icmp slt i32 %idx, %len
-  %abc = and i1 %c1, %c2
-  br i1 %abc, label %in.bounds, label %out.of.bounds
-
-in.bounds:
-  %addr = getelementptr i32, i32* %arr, i32 %idx
-  store i32 0, i32* %addr
-  %next = icmp slt i32 %idx, 100
-  br i1 %next, label %loop, label %exit
-
-out.of.bounds:
-  ret void
-
-exit:
-  ret void
-}
-
-!0 = !{i32 0, i32 50}
-!1 = !{i64 0, i64 50}