X86 address mode isel tweak. If the base of the address is also used by a CopyToReg (i.e. it's likely live-out), do not fold the sub-expressions into the addressing mode to avoid computing the address twice. The CopyToReg use will be isel'ed to a LEA, re-use it for address instead.

This is not yet enabled.

llvm-svn: 68082

1 files changed, 25 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index 9caf1842eb8..4bc604b6e46 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -41,6 +41,9 @@
 #include "llvm/ADT/Statistic.h"
 using namespace llvm;
 
+#include "llvm/Support/CommandLine.h"
+static cl::opt<bool> AvoidDupAddrCompute("x86-avoid-dup-address", cl::Hidden);
+
 STATISTIC(NumLoadMoved, "Number of loads moved below TokenFactor");
 
 //===----------------------------------------------------------------------===//
@@ -1035,7 +1038,28 @@ bool X86DAGToDAGISel::SelectAddr(SDValue Op, SDValue N, SDValue &Base,
                                  SDValue &Scale, SDValue &Index,
                                  SDValue &Disp) {
   X86ISelAddressMode AM;
-  if (MatchAddress(N, AM))
+  bool Done = false;
+  if (AvoidDupAddrCompute && !N.hasOneUse()) {
+    unsigned Opcode = N.getOpcode();
+    if (Opcode != ISD::Constant && Opcode != ISD::FrameIndex &&
+        Opcode != X86ISD::Wrapper) {
+      // If we are able to fold N into addressing mode, then we'll allow it even
+      // if N has multiple uses. In general, addressing computation is used as
+      // addresses by all of its uses. But watch out for CopyToReg uses, that
+      // means the address computation is liveout. It will be computed by a LEA
+      // so we want to avoid computing the address twice.
+      for (SDNode::use_iterator UI = N.getNode()->use_begin(),
+             UE = N.getNode()->use_end(); UI != UE; ++UI) {
+        if (UI->getOpcode() == ISD::CopyToReg) {
+          MatchAddressBase(N, AM, true, 0);
+          Done = true;
+          break;
+        }
+      }
+    }
+  }
+
+  if (!Done && MatchAddress(N, AM))
     return false;
 
   MVT VT = N.getValueType();