Merge pull request rust-lang#150 from vext01/vlmap-tweak

Yk IR serialiser: Simplify the value lowering map.

Author: ltratt

llvm/lib/YkIR/YkIRWriter.cpp

@@ -135,13 +135,20 @@ template <class C, class E> size_t getIndex(C *Container, E *FindElement) {
   return Idx;
 }
 
-// A <BBIdx, InstrIdx> pair that Uniquely identifies an Yk IR instruction within
-// a function.
-using InstrLoc = std::tuple<size_t, size_t>;
+// An instruction index that uniquely identifies an Yk instruction within
+// a basic block.
+//
+// FIXME: At some point it may be worth making type-safe index types (for
+// instruction, block and function indices) and using them throughout
+// the serialiser.
+using InstIdx = size_t;
 
-// Maps an LLVM instruction that generates a value to the corresponding Yk IR
-// instruction.
-using ValueLoweringMap = map<Instruction *, InstrLoc>;
+// Maps an LLVM local (the instruction that creates it) to the correspoinding Yk
+// instruction index in its parent basic block.
+//
+// Note: The Yk basic block index is not stored because it's the same as
+// the LLVM IR block index, which can be found elsewhere (see `getIndex()`).
+using ValueLoweringMap = map<Instruction *, InstIdx>;
 
 // Function lowering context.
 //
@@ -169,18 +176,18 @@ class FuncLowerCtxt {
   void patchUpInstIdxs(MCStreamer &OutStreamer) {
     MCContext &MCtxt = OutStreamer.getContext();
     for (auto &[Inst, Sym] : InstIdxPatchUps) {
-      auto [_, InstIdx] = VLMap.at(Inst);
+      InstIdx InstIdx = VLMap.at(Inst);
       OutStreamer.emitAssignment(Sym, MCConstantExpr::create(InstIdx, MCtxt));
     }
   }
 
   // Add/update an entry in the value lowering map.
-  void updateVLMap(Instruction *I, InstrLoc L) { VLMap[I] = L; }
+  void updateVLMap(Instruction *I, InstIdx L) { VLMap[I] = L; }
 
   // Get the entry for `I` in the value lowering map.
   //
   // Raises `std::out_of_range` if not present.
-  InstrLoc lookupInVLMap(Instruction *I) { return VLMap.at(I); }
+  InstIdx lookupInVLMap(Instruction *I) { return VLMap.at(I); }
 
   // Determines if there's an entry for `I` in the value lowering map.
   bool vlMapContains(Instruction *I) { return VLMap.count(I) == 1; }
@@ -289,12 +296,16 @@ class YkIRWriter {
   }
 
   void serialiseLocalVariableOperand(Instruction *I, FuncLowerCtxt &FLCtxt) {
+    // operand kind:
     serialiseOperandKind(OperandKindLocal);
+    // func_idx:
     OutStreamer.emitSizeT(getIndex(&M, I->getFunction()));
+    // bb_idx:
+    OutStreamer.emitSizeT(getIndex(I->getFunction(), I->getParent()));
 
+    // inst_idx:
     if (FLCtxt.vlMapContains(I)) {
-      auto [BBIdx, InstIdx] = FLCtxt.lookupInVLMap(I);
-      OutStreamer.emitSizeT(BBIdx);
+      InstIdx InstIdx = FLCtxt.lookupInVLMap(I);
       OutStreamer.emitSizeT(InstIdx);
     } else {
       // It's a local variable generated by an instruction that we haven't
@@ -303,16 +314,7 @@ class YkIRWriter {
       //
       // To work around this, we emit a dummy instruction index
       // and patch it up later once it becomes known.
-      //
-      // The basic block index can be immediately known, since the indices are
-      // the same in the LLVM IR and our AOT IR.
-      //
-      // FIXME: In light of the above, there's no need to store basic block
-      // indices in the VLMap?
-      OutStreamer.emitSizeT(getIndex(I->getFunction(), I->getParent()));
-
-      MCContext &MCtxt = OutStreamer.getContext();
-      MCSymbol *PatchUpSym = MCtxt.createTempSymbol();
+      MCSymbol *PatchUpSym = OutStreamer.getContext().createTempSymbol();
       OutStreamer.emitSymbolValue(PatchUpSym, sizeof(size_t));
       FLCtxt.deferInstIdx(I, PatchUpSym);
     }
@@ -375,7 +377,7 @@ class YkIRWriter {
     // right-hand side:
     serialiseOperand(I, FLCtxt, I->getOperand(1));
 
-    FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+    FLCtxt.updateVLMap(I, InstIdx);
     InstIdx++;
   }
 
@@ -457,7 +459,7 @@ class YkIRWriter {
     // XXX guard cast
     OutStreamer.emitSizeT(CI->getZExtValue());
 
-    FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+    FLCtxt.updateVLMap(I, InstIdx);
     InstIdx++;
   }
 
@@ -540,7 +542,7 @@ class YkIRWriter {
 
     // If the return type is non-void, then this defines a local.
     if (!I->getType()->isVoidTy()) {
-      FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+      FLCtxt.updateVLMap(I, InstIdx);
     }
     InstIdx++;
   }
@@ -585,7 +587,7 @@ class YkIRWriter {
     // type_idx:
     OutStreamer.emitSizeT(typeIndex(I->getType()));
 
-    FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+    FLCtxt.updateVLMap(I, InstIdx);
     InstIdx++;
   }
 
@@ -619,7 +621,7 @@ class YkIRWriter {
     // offset:
     serialiseOperand(I, FLCtxt, ConstantInt::get(I->getContext(), Offset));
 
-    FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+    FLCtxt.updateVLMap(I, InstIdx);
     InstIdx++;
   }
 
@@ -676,7 +678,7 @@ class YkIRWriter {
     // rhs:
     serialiseOperand(I, FLCtxt, I->getOperand(1));
 
-    FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+    FLCtxt.updateVLMap(I, InstIdx);
     InstIdx++;
   }
 
@@ -725,7 +727,7 @@ class YkIRWriter {
     // dest_type_idx:
     OutStreamer.emitSizeT(typeIndex(I->getDestTy()));
 
-    FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+    FLCtxt.updateVLMap(I, InstIdx);
     InstIdx++;
   }
 
@@ -772,7 +774,7 @@ class YkIRWriter {
       serialiseOperand(I, FLCtxt, I->getIncomingValue(J));
     }
 
-    FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+    FLCtxt.updateVLMap(I, InstIdx);
     InstIdx++;
   }
 
@@ -812,7 +814,7 @@ class YkIRWriter {
     serialiseString(toString(I));
 
     if (!I->getType()->isVoidTy()) {
-      FLCtxt.updateVLMap(I, {BBIdx, InstIdx});
+      FLCtxt.updateVLMap(I, InstIdx);
     }
     InstIdx++;
   }