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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57748 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 47 insertions, 2 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 4b1945efe4..81058152eb 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -967,6 +967,13 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
   // fold (add x, 0) -> x
   if (N1C && N1C->isNullValue())
     return N0;
+  // fold (add Sym, c) -> Sym+c
+  if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(N0))
+    if (!AfterLegalize && TLI.isOffsetFoldingLegal(GA) && N1C &&
+        GA->getOpcode() == ISD::GlobalAddress)
+      return DAG.getGlobalAddress(GA->getGlobal(), VT,
+                                  GA->getOffset() +
+                                    (uint64_t)N1C->getSExtValue());
   // fold ((c1-A)+c2) -> (c1+c2)-A
   if (N1C && N0.getOpcode() == ISD::SUB)
     if (ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0.getOperand(0)))
@@ -1133,6 +1140,21 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
   if (N1.getOpcode() == ISD::UNDEF)
     return N1;
 
+  // If the relocation model supports it, consider symbol offsets.
+  if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(N0))
+    if (!AfterLegalize && TLI.isOffsetFoldingLegal(GA)) {
+      // fold (sub Sym, c) -> Sym-c
+      if (N1C && GA->getOpcode() == ISD::GlobalAddress)
+        return DAG.getGlobalAddress(GA->getGlobal(), VT,
+                                    GA->getOffset() -
+                                      (uint64_t)N1C->getSExtValue());
+      // fold (sub Sym+c1, Sym+c2) -> c1-c2
+      if (GlobalAddressSDNode *GB = dyn_cast<GlobalAddressSDNode>(N1))
+        if (GA->getGlobal() == GB->getGlobal())
+          return DAG.getConstant((uint64_t)GA->getOffset() - GB->getOffset(),
+                                 VT);
+    }
+
   return SDValue();
 }
 
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9cfb1a1a22..07819404e1 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -959,10 +959,15 @@ SDValue SelectionDAG::getConstantFP(double Val, MVT VT, bool isTarget) {
 }
 
 SDValue SelectionDAG::getGlobalAddress(const GlobalValue *GV,
-                                       MVT VT, int Offset,
+                                       MVT VT, int64_t Offset,
                                        bool isTargetGA) {
   unsigned Opc;
 
+  // Truncate (with sign-extension) the offset value to the pointer size.
+  unsigned BitWidth = VT.getSizeInBits();
+  if (BitWidth < 64)
+    Offset = (Offset << (64 - BitWidth) >> (64 - BitWidth));
+
   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
   if (!GVar) {
     // If GV is an alias then use the aliasee for determining thread-localness.
@@ -2017,6 +2022,7 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{
 bool SelectionDAG::isVerifiedDebugInfoDesc(SDValue Op) const {
   GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Op);
   if (!GA) return false;
+  if (GA->getOffset() != 0) return false;
   GlobalVariable *GV = dyn_cast<GlobalVariable>(GA->getGlobal());
   if (!GV) return false;
   MachineModuleInfo *MMI = getMachineModuleInfo();
@@ -4726,7 +4732,7 @@ HandleSDNode::~HandleSDNode() {
 }
 
 GlobalAddressSDNode::GlobalAddressSDNode(bool isTarget, const GlobalValue *GA,
-                                         MVT VT, int o)
+                                         MVT VT, int64_t o)
   : SDNode(isa<GlobalVariable>(GA) &&
            cast<GlobalVariable>(GA)->isThreadLocal() ?
            // Thread Local
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 479e1380c5..1e7e847b8a 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -656,6 +656,23 @@ SDValue TargetLowering::getPICJumpTableRelocBase(SDValue Table,
   return Table;
 }
 
+bool
+TargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
+  // Assume that everything is safe in static mode.
+  if (getTargetMachine().getRelocationModel() == Reloc::Static)
+    return true;
+
+  // In dynamic-no-pic mode, assume that known defined values are safe.
+  if (getTargetMachine().getRelocationModel() == Reloc::DynamicNoPIC &&
+      GA &&
+      !GA->getGlobal()->isDeclaration() &&
+      !GA->getGlobal()->mayBeOverridden())
+    return true;
+
+  // Otherwise assume nothing is safe.
+  return false;
+}
+
 //===----------------------------------------------------------------------===//
 //  Optimization Methods
 //===----------------------------------------------------------------------===//