Revert "[DebugInfo] Improve dbg preservation in LSR."

This reverts commit a3caf7f.

The ReleaseLTO-g test-suite configuration has been failing
to build since this commit, because clang segfaults while
building 7zip.

Author: nikic

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -1117,15 +1117,6 @@ class ScalarEvolution {
       const SCEV *S, const Loop *L,
       SmallPtrSetImpl<const SCEVPredicate *> &Preds);
 
-  /// Compute \p LHS - \p RHS and returns the result as an APInt if it is a
-  /// constant, and None if it isn't.
-  ///
-  /// This is intended to be a cheaper version of getMinusSCEV.  We can be
-  /// frugal here since we just bail out of actually constructing and
-  /// canonicalizing an expression in the cases where the result isn't going
-  /// to be a constant.
-  Optional<APInt> computeConstantDifference(const SCEV *LHS, const SCEV *RHS);
-
 private:
   /// A CallbackVH to arrange for ScalarEvolution to be notified whenever a
   /// Value is deleted.
@@ -1808,6 +1799,15 @@ class ScalarEvolution {
   bool splitBinaryAdd(const SCEV *Expr, const SCEV *&L, const SCEV *&R,
                       SCEV::NoWrapFlags &Flags);
 
+  /// Compute \p LHS - \p RHS and returns the result as an APInt if it is a
+  /// constant, and None if it isn't.
+  ///
+  /// This is intended to be a cheaper version of getMinusSCEV.  We can be
+  /// frugal here since we just bail out of actually constructing and
+  /// canonicalizing an expression in the cases where the result isn't going
+  /// to be a constant.
+  Optional<APInt> computeConstantDifference(const SCEV *LHS, const SCEV *RHS);
+
   /// Drop memoized information computed for S.
   void forgetMemoizedResults(const SCEV *S);
 

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -59,7 +59,6 @@
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/SetOperations.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallBitVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
@@ -81,7 +80,6 @@
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
-#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/GlobalValue.h"
@@ -5778,27 +5776,6 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
   if (MSSA)
     MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
 
-  // Debug preservation - record all llvm.dbg.value from the loop as well as
-  // the SCEV of their variable location. Since salvageDebugInfo may change the
-  // DIExpression we need to store the original here as well (i.e. it needs to
-  // be in sync with the SCEV).
-  SmallVector<
-      std::tuple<DbgValueInst *, const Type *, const SCEV *, DIExpression *>,
-      32>
-      DbgValues;
-  for (auto &B : L->getBlocks()) {
-    for (auto &I : *B) {
-      if (DbgValueInst *D = dyn_cast<DbgValueInst>(&I)) {
-        auto V = D->getVariableLocation();
-        if (!SE.isSCEVable(V->getType()))
-          continue;
-        auto DS = SE.getSCEV(V);
-        DbgValues.push_back(
-            std::make_tuple(D, V->getType(), DS, D->getExpression()));
-      }
-    }
-  }
-
   // Run the main LSR transformation.
   Changed |=
       LSRInstance(L, IU, SE, DT, LI, TTI, AC, TLI, MSSAU.get()).getChanged();
@@ -5820,40 +5797,6 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
       DeleteDeadPHIs(L->getHeader(), &TLI, MSSAU.get());
     }
   }
-  // Debug preservation - go through all recorded llvm.dbg.value and for those
-  // that now have an undef variable location use the recorded SCEV to try and
-  // update it. Compare with SCEV of Phi-nodes of loop header to find a
-  // suitable update candidate. SCEV match with constant offset is allowed and
-  // will be compensated for in the DIExpression.
-  if (Changed) {
-    for (auto &D : DbgValues) {
-      auto DbgValue = std::get<DbgValueInst *>(D);
-      auto DbgValueType = std::get<const Type *>(D);
-      auto DbgValueSCEV = std::get<const SCEV *>(D);
-      auto DbgDIExpr = std::get<DIExpression *>(D);
-      if (!isa<UndefValue>(DbgValue->getVariableLocation()))
-        continue;
-      for (PHINode &Phi : L->getHeader()->phis()) {
-        if (DbgValueType != Phi.getType())
-          continue;
-        if (!SE.isSCEVable(Phi.getType()))
-          continue;
-        auto PhiSCEV = SE.getSCEV(&Phi);
-        if (Optional<APInt> Offset =
-                SE.computeConstantDifference(DbgValueSCEV, PhiSCEV)) {
-          auto &Ctx = DbgValue->getContext();
-          DbgValue->setOperand(
-              0, MetadataAsValue::get(Ctx, ValueAsMetadata::get(&Phi)));
-          if (Offset.getValue().getSExtValue()) {
-            SmallVector<uint64_t, 8> Ops;
-            DIExpression::appendOffset(Ops, Offset.getValue().getSExtValue());
-            DbgDIExpr = DIExpression::prependOpcodes(DbgDIExpr, Ops, true);
-          }
-          DbgValue->setOperand(2, MetadataAsValue::get(Ctx, DbgDIExpr));
-        }
-      }
-    }
-  }
   return Changed;
 }
 

llvm/test/DebugInfo/COFF/fpo-shrink-wrap.ll

@@ -33,7 +33,7 @@
 ; ASM:         popl    %ebx
 ; ASM: [[EPILOGUE]]:                                 # %return
 ; ASM:         retl    $8
-; ASM: Ltmp11:
+; ASM: Ltmp10:
 ; ASM:         .cv_fpo_endproc
 
 ; Note how RvaStart advances 7 bytes to skip the shrink-wrapped portion.