1 files changed, 43 insertions, 1 deletions

diff --git a/polly/lib/CodeGen/BlockGenerators.cpp b/polly/lib/CodeGen/BlockGenerators.cpp
index 5b576e1657d..bae65907a41 100644
--- a/polly/lib/CodeGen/BlockGenerators.cpp
+++ b/polly/lib/CodeGen/BlockGenerators.cpp
@@ -270,7 +270,8 @@ void BlockGenerator::copyInstruction(ScopStmt &Stmt, const Instruction *Inst,
   Loop *L = getLoopForInst(Inst);
   if ((Stmt.isBlockStmt() || !Stmt.getRegion()->contains(L)) &&
       canSynthesize(Inst, &LI, &SE, &Stmt.getParent()->getRegion())) {
-    // Synthesizable statements will be generated on-demand.
+    Value *NewValue = getNewValue(Stmt, Inst, BBMap, LTS, L);
+    BBMap[Inst] = NewValue;
     return;
   }
 
@@ -300,6 +301,28 @@ void BlockGenerator::copyInstruction(ScopStmt &Stmt, const Instruction *Inst,
   copyInstScalar(Stmt, Inst, BBMap, LTS);
 }
 
+/// @brief Remove trivially dead instructions from BB
+///
+/// This function drops trivially dead instructions from a basic block. It
+/// on purpose does _not_ recurse into other BBs even if the deletion of
+/// instructions in this basic block can make instructions in other basic blocks
+/// triviall dead.
+static void simplifyInstsInBlockOnly(BasicBlock *BB) {
+  auto BI = --BB->end(), BE = BB->begin();
+  bool Exit = false;
+  while (!Exit) {
+    auto ToRemove = BI;
+    if (BI != BE)
+      BI--;
+    else
+      Exit = true;
+
+    if (!isInstructionTriviallyDead(ToRemove))
+      continue;
+    ToRemove->eraseFromParent();
+  }
+}
+
 void BlockGenerator::copyStmt(ScopStmt &Stmt, LoopToScevMapT &LTS,
                               isl_id_to_ast_expr *NewAccesses) {
   assert(Stmt.isBlockStmt() &&
@@ -309,6 +332,16 @@ void BlockGenerator::copyStmt(ScopStmt &Stmt, LoopToScevMapT &LTS,
 
   BasicBlock *BB = Stmt.getBasicBlock();
   copyBB(Stmt, BB, BBMap, LTS, NewAccesses);
+
+  auto CopyBB = Builder.GetInsertBlock();
+  // Delete trivially dead instructions in CopyBB, but not in any other BB.
+  // Only for copyBB we know that there will _never_ be any future uses of
+  // instructions that have no use after copyBB has finished. Other instructions
+  // in the AST that have been generated by IslNodeBuilder may look dead at
+  // the moment, but may possibly still be referenced by GlobalMaps. If we
+  // delete them now, later uses would break surprisingly.
+  simplifyInstsInBlockOnly(CopyBB);
+  Builder.SetInsertPoint(CopyBB->getTerminator());
 }
 
 BasicBlock *BlockGenerator::splitBB(BasicBlock *BB) {
@@ -1099,6 +1132,15 @@ void RegionGenerator::copyStmt(ScopStmt &Stmt, LoopToScevMapT &LTS,
     LTS[L] = SE.getUnknown(LoopPHI);
   }
 
+  // Delete trivially dead instructions in CopyBB, but not in any other BB.
+  // Only for copyBB we know that there will _never_ be any future uses of
+  // instructions that have no use after copyBB has finished. Other instructions
+  // in the AST that have been generated by IslNodeBuilder may look dead at
+  // the moment, but may possibly still be referenced by GlobalMaps. If we
+  // delete them now, later uses would break surprisingly.
+  for (auto *BB : SeenBlocks)
+    simplifyInstsInBlockOnly(BlockMap[BB]);
+
   // Reset the old insert point for the build.
   Builder.SetInsertPoint(ExitBBCopy->begin());
 }