[PATCH] D15923: Promote aggregate store to memset when possible

[Amaury SECHET via llvm-commits]

deadalnix created this revision.
deadalnix added reviewers: craig.topper, spatel, dexonsmith, Prazek, chandlerc, joker.eph, majnemer.
deadalnix added a subscriber: llvm-commits.

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

http://reviews.llvm.org/D15923

Files:
  lib/Transforms/Scalar/MemCpyOptimizer.cpp
  test/Transforms/MemCpyOpt/fca2memcpy.ll

Index: test/Transforms/MemCpyOpt/fca2memcpy.ll
===================================================================
--- test/Transforms/MemCpyOpt/fca2memcpy.ll
+++ test/Transforms/MemCpyOpt/fca2memcpy.ll
@@ -37,8 +37,10 @@
 
 define void @destroysrc(%S* %src, %S* %dst) {
 ; CHECK-LABEL: destroysrc
-; CHECK-NOT: call
-; CHECK: ret void
+; CHECK: load %S, %S* %src
+; CHECK: call void @llvm.memset.p0i8.i64
+; CHECK-NEXT: store %S %1, %S* %dst
+; CHECK-NEXT: ret void
   %1 = load %S, %S* %src
   store %S zeroinitializer, %S* %src
   store %S %1, %S* %dst
@@ -49,7 +51,7 @@
 ; CHECK-LABEL: destroynoaliassrc
 ; CHECK-NOT: load
 ; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64
-; CHECK-NEXT: store %S zeroinitializer, %S* %src
+; CHECK-NEXT: call void @llvm.memset.p0i8.i64
 ; CHECK-NEXT: ret void
   %1 = load %S, %S* %src
   store %S zeroinitializer, %S* %src
Index: lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -534,7 +534,6 @@
           for (; I != E; ++I) {
             MemoryLocation StoreLoc = MemoryLocation::get(SI);
             if (AA.getModRefInfo(&*I, StoreLoc) != MRI_NoModRef) {
-              DEBUG(dbgs() << "Alias " << *I << "\n");
               P = nullptr;
               break;
             }
@@ -628,13 +627,36 @@
   // 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;
     }
 
+    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;
 }
 


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