[Serialization] Preserve the order of basic blocks in SIL deserialization.

This shouldn't affect anything in practice but it's best to be deterministic.
(Although I'm not sure why the previous mode was nondeterministic.)

Swift SVN r28580

Author: jrose-apple

lib/Serialization/DeserializeSIL.cpp

@@ -251,18 +251,21 @@ SILValue SILDeserializer::getLocalValue(ValueID Id, unsigned ResultNum,
 
 /// Return the SILBasicBlock of a given ID.
 SILBasicBlock *SILDeserializer::getBBForDefinition(SILFunction *Fn,
+                                                   SILBasicBlock *Prev,
                                                    unsigned ID) {
   SILBasicBlock *&BB = BlocksByID[ID];
   // If the block has never been named yet, just create it.
   if (BB == nullptr)
-    return BB = new (SILMod) SILBasicBlock(Fn);
+    return BB = new (SILMod) SILBasicBlock(Fn, Prev);
 
   // If it already exists, it was either a forward reference or a redefinition.
   // The latter should never happen.
   bool wasForwardReferenced = UndefinedBlocks.erase(BB);
   assert(wasForwardReferenced);
   (void)wasForwardReferenced;
 
+  if (Prev)
+    BB->moveAfter(Prev);
   return BB;
 }
 
@@ -531,7 +534,7 @@ SILFunction *SILDeserializer::readSILFunction(DeclID FID,
          kind != SIL_WITNESSTABLE) {
     if (kind == SIL_BASIC_BLOCK)
       // Handle a SILBasicBlock record.
-      CurrentBB = readSILBasicBlock(fn, scratch);
+      CurrentBB = readSILBasicBlock(fn, CurrentBB, scratch);
     else {
       // If CurrentBB is empty, just return fn. The code in readSILInstruction
       // assumes that such a situation means that fn is a declaration. Thus it
@@ -570,13 +573,14 @@ SILFunction *SILDeserializer::readSILFunction(DeclID FID,
 }
 
 SILBasicBlock *SILDeserializer::readSILBasicBlock(SILFunction *Fn,
+                                                  SILBasicBlock *Prev,
                                     SmallVectorImpl<uint64_t> &scratch) {
   ArrayRef<uint64_t> Args;
   SILBasicBlockLayout::readRecord(scratch, Args);
 
   // Args should be a list of pairs, the first number is a TypeID, the
   // second number is a ValueID.
-  SILBasicBlock *CurrentBB = getBBForDefinition(Fn, BasicBlockID++);
+  SILBasicBlock *CurrentBB = getBBForDefinition(Fn, Prev, BasicBlockID++);
   for (unsigned I = 0, E = Args.size(); I < E; I += 3) {
     TypeID TyID = Args[I];
     if (!TyID) return nullptr;

lib/Serialization/DeserializeSIL.h

@@ -65,14 +65,16 @@ namespace swift {
 
     /// Return the SILBasicBlock of a given ID.
     SILBasicBlock *getBBForReference(SILFunction *Fn, unsigned ID);
-    SILBasicBlock *getBBForDefinition(SILFunction *Fn, unsigned ID);
+    SILBasicBlock *getBBForDefinition(SILFunction *Fn, SILBasicBlock *Prev,
+                                      unsigned ID);
 
     /// Read a SIL function.
     SILFunction *readSILFunction(serialization::DeclID, SILFunction *InFunc,
                                  StringRef Name, bool declarationOnly,
                                  bool errorIfEmptyBody = true);
     /// Read a SIL basic block within a given SIL function.
     SILBasicBlock *readSILBasicBlock(SILFunction *Fn,
+                                     SILBasicBlock *Prev,
                                      SmallVectorImpl<uint64_t> &scratch);
     /// Read a SIL instruction within a given SIL basic block.
     bool readSILInstruction(SILFunction *Fn, SILBasicBlock *BB,

test/Serialization/Inputs/def_basic.sil

@@ -76,11 +76,10 @@ bb1:
 // CHECK-LABEL: sil public_external [fragile] @test2 : $@convention(thin) (Int) -> ()
 sil [fragile] @test2 : $@convention(thin) (Int) -> () {
   // CHECK: bb1:
-  // CHECK: %2 = tuple ()
-  // CHECK: br bb2
+  // CHECK: return %5 : $()
   // CHECK: bb2:
-  // FIXME: should be %2
-  // CHECK: return %{{.*}} : $()
+  // CHECK: %5 = tuple ()
+  // CHECK: br bb1
 bb0(%0 : $Int):
   br bb2
 bb1: