Promote aggregate store to memset when possible

Summary: As per title. This will allow the optimizer to pick up on it.

Reviewers: craig.topper, spatel, dexonsmith, Prazek, chandlerc, joker.eph, majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15923

llvm-svn: 256969

1 files changed, 27 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 849bd27b442..5711a775df8 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -627,13 +627,39 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
   // Ensure that the value being stored is something that can be memset'able a
   // byte at a time like "0" or "-1" or any width, as well as things like
   // 0xA0A0A0A0 and 0.0.
-  if (Value *ByteVal = isBytewiseValue(SI->getOperand(0)))
+  auto *V = SI->getOperand(0);
+  if (Value *ByteVal = isBytewiseValue(V)) {
     if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
                                               ByteVal)) {
       BBI = I->getIterator(); // Don't invalidate iterator.
       return true;
     }
 
+    // If we have an aggregate, we try to promote it to memset regardless
+    // of opportunity for merging as it can expose optimization opportunities
+    // in subsequent passes.
+    auto *T = V->getType();
+    if (T->isAggregateType()) {
+      uint64_t Size = DL.getTypeStoreSize(T);
+      unsigned Align = SI->getAlignment();
+      if (!Align)
+        Align = DL.getABITypeAlignment(T);
+      IRBuilder<> Builder(SI);
+      auto *M = Builder.CreateMemSet(SI->getPointerOperand(), ByteVal,
+                                     Size, Align, SI->isVolatile());
+
+      DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n");
+
+      MD->removeInstruction(SI);
+      SI->eraseFromParent();
+      NumMemSetInfer++;
+
+      // Make sure we do not invalidate the iterator.
+      BBI = M->getIterator();
+      return true;
+    }
+  }
+
   return false;
 }