Implement support for x86 fastisel of small fixed-sized memcpys, which are generated

en-mass for C++ PODs.  On my c++ test file, this cuts the fast isel rejects by 10x 
and shrinks the generated .s file by 5%

llvm-svn: 129755

lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -486,8 +486,7 @@ bool FastISel::SelectCall(const User *I) {
   if (!F) return false;
 
   // Handle selected intrinsic function calls.
-  unsigned IID = F->getIntrinsicID();
-  switch (IID) {
+  switch (F->getIntrinsicID()) {
   default: break;
   case Intrinsic::dbg_declare: {
     const DbgDeclareInst *DI = cast<DbgDeclareInst>(I);
@@ -552,9 +551,9 @@ bool FastISel::SelectCall(const User *I) {
   }
   case Intrinsic::eh_exception: {
     EVT VT = TLI.getValueType(I->getType());
-    switch (TLI.getOperationAction(ISD::EXCEPTIONADDR, VT)) {
-    default: break;
-    case TargetLowering::Expand: {
+    if (TLI.getOperationAction(ISD::EXCEPTIONADDR, VT)!=TargetLowering::Expand)
+      break;
+    
     assert(FuncInfo.MBB->isLandingPad() &&
            "Call to eh.exception not in landing pad!");
     unsigned Reg = TLI.getExceptionAddressRegister();
@@ -565,14 +564,10 @@ bool FastISel::SelectCall(const User *I) {
     UpdateValueMap(I, ResultReg);
     return true;
   }
-    }
-    break;
-  }
   case Intrinsic::eh_selector: {
     EVT VT = TLI.getValueType(I->getType());
-    switch (TLI.getOperationAction(ISD::EHSELECTION, VT)) {
-    default: break;
-    case TargetLowering::Expand: {
+    if (TLI.getOperationAction(ISD::EHSELECTION, VT) != TargetLowering::Expand)
+      break;
     if (FuncInfo.MBB->isLandingPad())
       AddCatchInfo(*cast<CallInst>(I), &FuncInfo.MF->getMMI(), FuncInfo.MBB);
     else {
@@ -609,9 +604,6 @@ bool FastISel::SelectCall(const User *I) {
     return true;
   }
   }
-    break;
-  }
-  }
 
   // An arbitrary call. Bail.
   return false;

lib/Target/X86/X86FastISel.cpp

@@ -1325,6 +1325,52 @@ bool X86FastISel::X86VisitIntrinsicCall(const IntrinsicInst &I) {
   // FIXME: Handle more intrinsics.
   switch (I.getIntrinsicID()) {
   default: return false;
+  case Intrinsic::memcpy: {
+    const MemCpyInst &MCI = cast<MemCpyInst>(I);
+    // Don't handle volatile or variable length memcpys.
+    if (MCI.isVolatile() || !isa<ConstantInt>(MCI.getLength()))
+      return false;
+    
+    // Don't inline super long memcpys.  We could lower these to a memcpy call,
+    // but we might as well bail out.
+    uint64_t Len = cast<ConstantInt>(MCI.getLength())->getZExtValue();
+    bool i64Legal = TLI.isTypeLegal(MVT::i64);
+    if (Len > (i64Legal ? 32 : 16)) return false;
+    
+    // Get the address of the dest and source addresses.
+    X86AddressMode DestAM, SrcAM;
+    if (!X86SelectAddress(MCI.getRawDest(), DestAM) ||
+        !X86SelectAddress(MCI.getRawSource(), SrcAM))
+      return false;
+    
+    // We don't care about alignment here since we just emit integer accesses.
+    while (Len) {
+      MVT VT;
+      if (Len >= 8 && i64Legal)
+        VT = MVT::i64;
+      else if (Len >= 4)
+        VT = MVT::i32;
+      else if (Len >= 2)
+        VT = MVT::i16;
+      else {
+        assert(Len == 1);
+        VT = MVT::i8;
+      }
+      
+      unsigned Reg;
+      bool RV = X86FastEmitLoad(VT, SrcAM, Reg);
+      RV &= X86FastEmitStore(VT, Reg, DestAM);
+      assert(RV && "Failed to emit load or store??");
+      
+      unsigned Size = VT.getSizeInBits()/8;
+      Len -= Size;
+      DestAM.Disp += Size;
+      SrcAM.Disp += Size;
+    }
+    
+    return true;
+  }
+      
   case Intrinsic::stackprotector: {
     // Emit code inline code to store the stack guard onto the stack.
     EVT PtrTy = TLI.getPointerTy();
@@ -1335,17 +1381,14 @@ bool X86FastISel::X86VisitIntrinsicCall(const IntrinsicInst &I) {
     // Grab the frame index.
     X86AddressMode AM;
     if (!X86SelectAddress(Slot, AM)) return false;
-
     if (!X86FastEmitStore(PtrTy, Op1, AM)) return false;
-
     return true;
   }
   case Intrinsic::objectsize: {
-    ConstantInt *CI = dyn_cast<ConstantInt>(I.getArgOperand(1));
+    // FIXME: This should be moved to generic code!
+    ConstantInt *CI = cast<ConstantInt>(I.getArgOperand(1));
     const Type *Ty = I.getCalledFunction()->getReturnType();
 
-    assert(CI && "Non-constant type in Intrinsic::objectsize?");
-
     MVT VT;
     if (!isTypeLegal(Ty, VT))
       return false;
@@ -1383,6 +1426,8 @@ bool X86FastISel::X86VisitIntrinsicCall(const IntrinsicInst &I) {
   }
   case Intrinsic::sadd_with_overflow:
   case Intrinsic::uadd_with_overflow: {
+    // FIXME: Should fold immediates.
+    
     // Replace "add with overflow" intrinsics with an "add" instruction followed
     // by a seto/setc instruction. Later on, when the "extractvalue"
     // instructions are encountered, we use the fact that two registers were

test/CodeGen/X86/fast-isel-x86-64.ll

@@ -170,3 +170,14 @@ entry:
 ; CHECK: callq
 }
 
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i32, i1)
+
+; rdar://9289488 - fast-isel shouldn't bail out on llvm.memcpy
+define void @test15(i8* %a, i8* %b) nounwind {
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* %b, i64 4, i32 4, i1 false)
+  ret void
+; CHECK: test15:
+; CHECK-NEXT: movl	(%rsi), %eax
+; CHECK-NEXT: movl	%eax, (%rdi)
+; CHECK-NEXT: ret
+}