[PowerPC] For larger offsets, when possible, fold offset into addis toc@ha

When we have an offset into a global, etc. that is accessed relative to the TOC
base pointer, and the offset is larger than the minimum alignment of the global
itself and the TOC base pointer (which is 8-byte aligned), we can still fold
the @toc@ha into the memory access, but we must update the addis instruction's
symbol reference with the offset as the symbol addend. When there is only one
use of the addi to be folded and only one use of the addis that would need its
symbol's offset adjusted, then we can make the adjustment and fold the @toc@l
into the memory access.

llvm-svn: 280545

1 files changed, 27 insertions, 2 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 23ee3e7312f..56e39221edf 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -4381,9 +4381,30 @@ void PPCDAGToDAGISel::PeepholePPC64() {
       MaxDisplacement = std::min((int) GV->getAlignment() - 1, MaxDisplacement);
     }
 
+    bool UpdateHBase = false;
+    SDValue HBase = Base.getOperand(0);
+
     int Offset = N->getConstantOperandVal(FirstOp);
-    if (Offset < 0 || Offset > MaxDisplacement)
-      continue;
+    if (Offset < 0 || Offset > MaxDisplacement) {
+      // If we have a addi(toc@l)/addis(toc@ha) pair, and the addis has only
+      // one use, then we can do this for any offset, we just need to also
+      // update the offset (i.e. the symbol addend) on the addis also.
+      if (Base.getMachineOpcode() != PPC::ADDItocL)
+        continue;
+
+      if (!HBase.isMachineOpcode() ||
+          HBase.getMachineOpcode() != PPC::ADDIStocHA)
+        continue;
+
+      if (!Base.hasOneUse() || !HBase.hasOneUse())
+        continue;
+
+      SDValue HImmOpnd = HBase.getOperand(1);
+      if (HImmOpnd != ImmOpnd)
+        continue;
+
+      UpdateHBase = true;
+    }
 
     // We found an opportunity.  Reverse the operands from the add
     // immediate and substitute them into the load or store.  If
@@ -4426,6 +4447,10 @@ void PPCDAGToDAGISel::PeepholePPC64() {
       (void)CurDAG->UpdateNodeOperands(N, ImmOpnd, Base.getOperand(0),
                                        N->getOperand(2));
 
+    if (UpdateHBase)
+      (void)CurDAG->UpdateNodeOperands(HBase.getNode(), HBase.getOperand(0),
+                                       ImmOpnd);
+
     // The add-immediate may now be dead, in which case remove it.
     if (Base.getNode()->use_empty())
       CurDAG->RemoveDeadNode(Base.getNode());