Teach DAGCombine to fold constant offsets into GlobalAddress nodes,

and add a TargetLowering hook for it to use to determine when this
is legal (i.e. not in PIC mode, etc.)

This allows instruction selection to emit folded constant offsets
in more cases, such as the included testcase, eliminating the need
for explicit arithmetic instructions.

This eliminates the need for the C++ code in X86ISelDAGToDAG.cpp
that attempted to achieve the same effect, but wasn't as effective.

Also, fix handling of offsets in GlobalAddressSDNodes in several
places, including changing GlobalAddressSDNode's offset from
int to int64_t.

The Mips, Alpha, Sparc, and CellSPU targets appear to be
unaware of GlobalAddress offsets currently, so set the hook to
false on those targets.

llvm-svn: 57748

1 files changed, 28 insertions, 7 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index fa467693bcf..c977dbe92b0 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -1705,7 +1705,8 @@ SDValue X86TargetLowering::LowerCALL(SDValue Op, SelectionDAG &DAG) {
     // non-JIT mode.
     if (!Subtarget->GVRequiresExtraLoad(G->getGlobal(),
                                         getTargetMachine(), true))
-      Callee = DAG.getTargetGlobalAddress(G->getGlobal(), getPointerTy());
+      Callee = DAG.getTargetGlobalAddress(G->getGlobal(), getPointerTy(),
+                                          G->getOffset());
   } else if (ExternalSymbolSDNode *S = dyn_cast<ExternalSymbolSDNode>(Callee)) {
     Callee = DAG.getTargetExternalSymbol(S->getSymbol(), getPointerTy());
   } else if (IsTailCall) {
@@ -4390,12 +4391,24 @@ X86TargetLowering::LowerConstantPool(SDValue Op, SelectionDAG &DAG) {
 
 SDValue
 X86TargetLowering::LowerGlobalAddress(const GlobalValue *GV,
+                                      int64_t Offset,
                                       SelectionDAG &DAG) const {
-  SDValue Result = DAG.getTargetGlobalAddress(GV, getPointerTy());
+  bool IsPic = getTargetMachine().getRelocationModel() == Reloc::PIC_;
+  bool ExtraLoadRequired =
+    Subtarget->GVRequiresExtraLoad(GV, getTargetMachine(), false);
+
+  // Create the TargetGlobalAddress node, folding in the constant
+  // offset if it is legal.
+  SDValue Result;
+  if (!IsPic && !ExtraLoadRequired) {
+    Result = DAG.getTargetGlobalAddress(GV, getPointerTy(), Offset);
+    Offset = 0;
+  } else
+    Result = DAG.getTargetGlobalAddress(GV, getPointerTy(), 0);
   Result = DAG.getNode(X86ISD::Wrapper, getPointerTy(), Result);
+
   // With PIC, the address is actually $g + Offset.
-  if (getTargetMachine().getRelocationModel() == Reloc::PIC_ &&
-      !Subtarget->isPICStyleRIPRel()) {
+  if (IsPic && !Subtarget->isPICStyleRIPRel()) {
     Result = DAG.getNode(ISD::ADD, getPointerTy(),
                          DAG.getNode(X86ISD::GlobalBaseReg, getPointerTy()),
                          Result);
@@ -4406,17 +4419,24 @@ X86TargetLowering::LowerGlobalAddress(const GlobalValue *GV,
   // the GlobalAddress must be in the base or index register of the address, not
   // the GV offset field. Platform check is inside GVRequiresExtraLoad() call
   // The same applies for external symbols during PIC codegen
-  if (Subtarget->GVRequiresExtraLoad(GV, getTargetMachine(), false))
+  if (ExtraLoadRequired)
     Result = DAG.getLoad(getPointerTy(), DAG.getEntryNode(), Result,
                          PseudoSourceValue::getGOT(), 0);
 
+  // If there was a non-zero offset that we didn't fold, create an explicit
+  // addition for it.
+  if (Offset != 0)
+    Result = DAG.getNode(ISD::ADD, getPointerTy(), Result,
+                         DAG.getConstant(Offset, getPointerTy()));
+
   return Result;
 }
 
 SDValue
 X86TargetLowering::LowerGlobalAddress(SDValue Op, SelectionDAG &DAG) {
   const GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
-  return LowerGlobalAddress(GV, DAG);
+  int64_t Offset = cast<GlobalAddressSDNode>(Op)->getOffset();
+  return LowerGlobalAddress(GV, Offset, DAG);
 }
 
 // Lower ISD::GlobalTLSAddress using the "general dynamic" model, 32 bit
@@ -7006,6 +7026,7 @@ bool X86TargetLowering::isGAPlusOffset(SDNode *N,
   if (N->getOpcode() == X86ISD::Wrapper) {
     if (isa<GlobalAddressSDNode>(N->getOperand(0))) {
       GA = cast<GlobalAddressSDNode>(N->getOperand(0))->getGlobal();
+      Offset = cast<GlobalAddressSDNode>(N->getOperand(0))->getOffset();
       return true;
     }
   }
@@ -7448,7 +7469,7 @@ void X86TargetLowering::LowerAsmOperandForConstraint(SDValue Op,
     
     if (GA) {
       if (hasMemory) 
-        Op = LowerGlobalAddress(GA->getGlobal(), DAG);
+        Op = LowerGlobalAddress(GA->getGlobal(), Offset, DAG);
       else
         Op = DAG.getTargetGlobalAddress(GA->getGlobal(), GA->getValueType(0),
                                         Offset);