[SROA] Thread the ability to add a pointer-specific name prefix through

the pointer adjustment code. This is the primary code path that creates
totally new instructions in SROA and being able to lump them based on
the pointer value's name for which they were created causes
*significantly* fewer name collisions and general noise in the debug
output. This is particularly significant because it is making it much
harder to track down instability in the output of SROA, as name
de-duplication is a totally harmless form of instability that gets in
the way of seeing real problems.

The new fancy naming scheme tries to dig out the root "pre-SROA" name
for pointer values and associate that all the way through the pointer
formation instructions. Digging out the root is important to prevent the
multiple iterative rounds of SROA from just layering too much cruft on
top of cruft here. We already track the layers of SROAs iteration in the
alloca name prefix. We don't need to duplicate it here.

Should have no functionality change, and shouldn't have any really
measurable impact on NDEBUG builds, as most of the complex logic is
debug-only.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202139 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SROA.cpp

@@ -1223,7 +1223,7 @@ static void speculateSelectInstLoads(SelectInst &SI) {
 /// This will return the BasePtr if that is valid, or build a new GEP
 /// instruction using the IRBuilder if GEP-ing is needed.
 static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
-                       SmallVectorImpl<Value *> &Indices) {
+                       SmallVectorImpl<Value *> &Indices, Twine NamePrefix) {
   if (Indices.empty())
     return BasePtr;
 
@@ -1232,7 +1232,7 @@ static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
   if (Indices.size() == 1 && cast<ConstantInt>(Indices.back())->isZero())
     return BasePtr;
 
-  return IRB.CreateInBoundsGEP(BasePtr, Indices, "idx");
+  return IRB.CreateInBoundsGEP(BasePtr, Indices, NamePrefix + "sroa_idx");
 }
 
 /// \brief Get a natural GEP off of the BasePtr walking through Ty toward
@@ -1246,9 +1246,10 @@ static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
 /// indicated by Indices to have the correct offset.
 static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
                                     Value *BasePtr, Type *Ty, Type *TargetTy,
-                                    SmallVectorImpl<Value *> &Indices) {
+                                    SmallVectorImpl<Value *> &Indices,
+                                    Twine NamePrefix) {
   if (Ty == TargetTy)
-    return buildGEP(IRB, BasePtr, Indices);
+    return buildGEP(IRB, BasePtr, Indices, NamePrefix);
 
   // See if we can descend into a struct and locate a field with the correct
   // type.
@@ -1275,7 +1276,7 @@ static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
   if (ElementTy != TargetTy)
     Indices.erase(Indices.end() - NumLayers, Indices.end());
 
-  return buildGEP(IRB, BasePtr, Indices);
+  return buildGEP(IRB, BasePtr, Indices, NamePrefix);
 }
 
 /// \brief Recursively compute indices for a natural GEP.
@@ -1285,9 +1286,10 @@ static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
 static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
                                        Value *Ptr, Type *Ty, APInt &Offset,
                                        Type *TargetTy,
-                                       SmallVectorImpl<Value *> &Indices) {
+                                       SmallVectorImpl<Value *> &Indices,
+                                       Twine NamePrefix) {
   if (Offset == 0)
-    return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices);
+    return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices, NamePrefix);
 
   // We can't recurse through pointer types.
   if (Ty->isPointerTy())
@@ -1307,7 +1309,7 @@ static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
     Offset -= NumSkippedElements * ElementSize;
     Indices.push_back(IRB.getInt(NumSkippedElements));
     return getNaturalGEPRecursively(IRB, DL, Ptr, VecTy->getElementType(),
-                                    Offset, TargetTy, Indices);
+                                    Offset, TargetTy, Indices, NamePrefix);
   }
 
   if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
@@ -1320,7 +1322,7 @@ static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
     Offset -= NumSkippedElements * ElementSize;
     Indices.push_back(IRB.getInt(NumSkippedElements));
     return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
-                                    Indices);
+                                    Indices, NamePrefix);
   }
 
   StructType *STy = dyn_cast<StructType>(Ty);
@@ -1339,7 +1341,7 @@ static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
 
   Indices.push_back(IRB.getInt32(Index));
   return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
-                                  Indices);
+                                  Indices, NamePrefix);
 }
 
 /// \brief Get a natural GEP from a base pointer to a particular offset and
@@ -1354,7 +1356,8 @@ static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
 /// If no natural GEP can be constructed, this function returns null.
 static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
                                       Value *Ptr, APInt Offset, Type *TargetTy,
-                                      SmallVectorImpl<Value *> &Indices) {
+                                      SmallVectorImpl<Value *> &Indices,
+                                      Twine NamePrefix) {
   PointerType *Ty = cast<PointerType>(Ptr->getType());
 
   // Don't consider any GEPs through an i8* as natural unless the TargetTy is
@@ -1373,7 +1376,7 @@ static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
   Offset -= NumSkippedElements * ElementSize;
   Indices.push_back(IRB.getInt(NumSkippedElements));
   return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
-                                  Indices);
+                                  Indices, NamePrefix);
 }
 
 /// \brief Compute an adjusted pointer from Ptr by Offset bytes where the
@@ -1391,8 +1394,9 @@ static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
 /// properties. The algorithm tries to fold as many constant indices into
 /// a single GEP as possible, thus making each GEP more independent of the
 /// surrounding code.
-static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL,
+static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr,
-                             Value *Ptr, APInt Offset, Type *PointerTy) {
+                             APInt Offset, Type *PointerTy,
+                             Twine NamePrefix) {
   // Even though we don't look through PHI nodes, we could be called on an
   // instruction in an unreachable block, which may be on a cycle.
   SmallPtrSet<Value *, 4> Visited;
@@ -1426,7 +1430,7 @@ static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL,
     // See if we can perform a natural GEP here.
     Indices.clear();
     if (Value *P = getNaturalGEPWithOffset(IRB, DL, Ptr, Offset, TargetTy,
-                                           Indices)) {
+                                           Indices, NamePrefix)) {
       if (P->getType() == PointerTy) {
         // Zap any offset pointer that we ended up computing in previous rounds.
         if (OffsetPtr && OffsetPtr->use_empty())
@@ -1461,19 +1465,19 @@ static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL,
   if (!OffsetPtr) {
     if (!Int8Ptr) {
       Int8Ptr = IRB.CreateBitCast(Ptr, IRB.getInt8PtrTy(),
-                                  "raw_cast");
+                                  NamePrefix + "sroa_raw_cast");
       Int8PtrOffset = Offset;
     }
 
     OffsetPtr = Int8PtrOffset == 0 ? Int8Ptr :
       IRB.CreateInBoundsGEP(Int8Ptr, IRB.getInt(Int8PtrOffset),
-                            "raw_idx");
+                            NamePrefix + "sroa_raw_idx");
   }
   Ptr = OffsetPtr;
 
   // On the off chance we were targeting i8*, guard the bitcast here.
   if (Ptr->getType() != PointerTy)
-    Ptr = IRB.CreateBitCast(Ptr, PointerTy, "cast");
+    Ptr = IRB.CreateBitCast(Ptr, PointerTy, NamePrefix + "sroa_cast");
 
   return Ptr;
 }
@@ -2046,9 +2050,35 @@ private:
   Value *getAdjustedAllocaPtr(IRBuilderTy &IRB, uint64_t Offset,
                               Type *PointerTy) {
     assert(Offset >= NewAllocaBeginOffset);
+#ifndef NDEBUG
+    StringRef OldName = OldPtr->getName();
+    // Skip through the last '.sroa.' component of the name.
+    size_t LastSROAPrefix = OldName.rfind(".sroa.");
+    if (LastSROAPrefix != StringRef::npos) {
+      OldName = OldName.substr(LastSROAPrefix + strlen(".sroa."));
+      // Look for an SROA slice index.
+      size_t IndexEnd = OldName.find_first_not_of("0123456789");
+      if (IndexEnd != StringRef::npos && OldName[IndexEnd] == '.') {
+        // Strip the index and look for the offset.
+        OldName = OldName.substr(IndexEnd + 1);
+        size_t OffsetEnd = OldName.find_first_not_of("0123456789");
+        if (OffsetEnd != StringRef::npos && OldName[OffsetEnd] == '.')
+          // Strip the offset.
+          OldName = OldName.substr(OffsetEnd + 1);
+      }
+    }
+    // Strip any SROA suffixes as well.
+    OldName = OldName.substr(0, OldName.find(".sroa_"));
+#endif
     return getAdjustedPtr(IRB, DL, &NewAI, APInt(DL.getPointerSizeInBits(),
                                                  Offset - NewAllocaBeginOffset),
-                          PointerTy);
+                          PointerTy,
+#ifndef NDEBUG
+                          Twine(OldName) + "."
+#else
+                          Twine()
+#endif
+                          );
   }
 
   /// \brief Compute suitable alignment to access an offset into the new alloca.
@@ -2527,7 +2557,8 @@ private:
 
       // Compute the other pointer, folding as much as possible to produce
       // a single, simple GEP in most cases.
-      OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, RelOffset, OtherPtrTy);
+      OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, RelOffset, OtherPtrTy,
+                                OtherPtr->getName() + ".");
 
       Value *OurPtr =
           getAdjustedAllocaPtr(IRB, NewBeginOffset, OldPtr->getType());
@@ -2569,7 +2600,8 @@ private:
       OtherPtrTy = SubIntTy->getPointerTo();
     }
 
-    Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, RelOffset, OtherPtrTy);
+    Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, RelOffset, OtherPtrTy,
+                                   OtherPtr->getName() + ".");
     Value *DstPtr = &NewAI;
     if (!IsDest)
       std::swap(SrcPtr, DstPtr);