[LoopVersioning] Add a check to see if the input loop is in LCSSA form

Loop Optimizations expect the input loop to be in LCSSA form. But it seems
that LoopVersioning doesn't have any check to see if the loop is actually in
LCSSA form. As a result, if we give it a loop which is not in LCSSA form but
still correct semantically, the resulting transformation fails to pass through
verifier pass with the following error.

Instruction does not dominate all uses!
%inc = add nsw i16 undef, 1
store i16 %inc, ptr @c, align 1

As the loop is not in LCSSA form, LoopVersioning's transformations leads to
invalid IR! As some instructions do not dominate all their uses.

This patch checks if a loop is in LCSSA form, if not it will call
formLCSSARecursively on the loop before passing it to LoopVersioning.

Fixes: #36998

llvm/lib/Transforms/Utils/LoopVersioning.cpp

@@ -27,6 +27,7 @@
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 
 using namespace llvm;
 
@@ -278,6 +279,9 @@ bool runImpl(LoopInfo *LI, LoopAccessInfoManager &LAIs, DominatorTree *DT,
     if (!LAI.hasConvergentOp() &&
         (LAI.getNumRuntimePointerChecks() ||
          !LAI.getPSE().getPredicate().isAlwaysTrue())) {
+      if (!L->isLCSSAForm(*DT))
+        llvm::formLCSSARecursively(*L, *DT, LI, SE);
+
       LoopVersioning LVer(LAI, LAI.getRuntimePointerChecking()->getChecks(), L,
                           LI, DT, SE);
       LVer.versionLoop();

llvm/test/Transforms/LoopVersioning/crash-36998.ll

@@ -0,0 +1,57 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=loop-versioning -aa-pipeline='' -S < %s | FileCheck %s
+target triple = "x86_64-unknown-linux-gnu"
+
+@a = external global i16, align 1
+@b = external global i16, align 1
+@c = external global i16, align 1
+
+define void @f2() {
+; CHECK-LABEL: define void @f2() {
+; CHECK-NEXT:  [[FOR_BODY_LVER_CHECK:.*:]]
+; CHECK-NEXT:    [[BOUND0:%.*]] = icmp ult ptr @b, getelementptr inbounds nuw (i8, ptr @a, i64 2)
+; CHECK-NEXT:    [[BOUND1:%.*]] = icmp ult ptr @a, getelementptr inbounds nuw (i8, ptr @b, i64 2)
+; CHECK-NEXT:    [[FOUND_CONFLICT:%.*]] = and i1 [[BOUND0]], [[BOUND1]]
+; CHECK-NEXT:    br i1 [[FOUND_CONFLICT]], label %[[FOR_BODY_PH_LVER_ORIG:.*]], label %[[FOR_BODY_PH:.*]]
+; CHECK:       [[FOR_BODY_PH_LVER_ORIG]]:
+; CHECK-NEXT:    br label %[[FOR_BODY_LVER_ORIG:.*]]
+; CHECK:       [[FOR_BODY_LVER_ORIG]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i16, ptr @a, align 1
+; CHECK-NEXT:    store i16 [[TMP0]], ptr @b, align 1
+; CHECK-NEXT:    [[INC_LVER_ORIG:%.*]] = add nsw i16 undef, 1
+; CHECK-NEXT:    br i1 false, label %[[FOR_BODY_LVER_ORIG]], label %[[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT:.*]]
+; CHECK:       [[FOR_BODY_PH]]:
+; CHECK-NEXT:    br label %[[FOR_BODY:.*]]
+; CHECK:       [[FOR_BODY]]:
+; CHECK-NEXT:    [[TMP1:%.*]] = load i16, ptr @a, align 1, !alias.scope [[META0:![0-9]+]]
+; CHECK-NEXT:    store i16 [[TMP1]], ptr @b, align 1, !alias.scope [[META3:![0-9]+]], !noalias [[META0]]
+; CHECK-NEXT:    [[INC:%.*]] = add nsw i16 undef, 1
+; CHECK-NEXT:    br i1 false, label %[[FOR_BODY]], label %[[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT1:.*]]
+; CHECK:       [[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT]]:
+; CHECK-NEXT:    [[INC_LCSSA_PH:%.*]] = phi i16 [ [[INC_LVER_ORIG]], %[[FOR_BODY_LVER_ORIG]] ]
+; CHECK-NEXT:    [[SPLIT2_PH:%.*]] = phi i16 [ [[INC_LVER_ORIG]], %[[FOR_BODY_LVER_ORIG]] ]
+; CHECK-NEXT:    br label %[[FOR_COND_FOR_END_CRIT_EDGE:.*]]
+; CHECK:       [[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT1]]:
+; CHECK-NEXT:    [[INC_LCSSA_PH2:%.*]] = phi i16 [ [[INC]], %[[FOR_BODY]] ]
+; CHECK-NEXT:    [[SPLIT2_PH3:%.*]] = phi i16 [ [[INC]], %[[FOR_BODY]] ]
+; CHECK-NEXT:    br label %[[FOR_COND_FOR_END_CRIT_EDGE]]
+; CHECK:       [[FOR_COND_FOR_END_CRIT_EDGE]]:
+; CHECK-NEXT:    [[INC_LCSSA:%.*]] = phi i16 [ [[INC_LCSSA_PH]], %[[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT]] ], [ [[INC_LCSSA_PH2]], %[[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT1]] ]
+; CHECK-NEXT:    [[SPLIT2:%.*]] = phi i16 [ [[SPLIT2_PH]], %[[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT]] ], [ [[SPLIT2_PH3]], %[[FOR_COND_FOR_END_CRIT_EDGE_LOOPEXIT1]] ]
+; CHECK-NEXT:    store i16 [[INC_LCSSA]], ptr @c, align 1
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %0 = load i16, ptr @a, align 1
+  store i16 %0, ptr @b, align 1
+  %inc = add nsw i16 undef, 1
+  br i1 false, label %for.body, label %for.cond.for.end_crit_edge
+
+for.cond.for.end_crit_edge:                       ; preds = %for.body
+  %split2 = phi i16 [ %inc, %for.body ]
+  store i16 %inc, ptr @c, align 1
+  ret void
+}