Fix PPC unaligned 64-bit loads and stores

PPC64 supports unaligned loads and stores of 64-bit values, but
in order to use the r+i forms, the offset must be a multiple of 4.
Unfortunately, this cannot always be determined by examining the
immediate itself because it might be available only via a TOC entry.

In order to get around this issue, we additionally predicate the
selection of the r+i form on the alignment of the load or store
(forcing it to be at least 4 in order to select the r+i form).

llvm-svn: 177338

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index a7e9d56fa9d..741e25e2001 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -1183,13 +1183,15 @@ bool PPCTargetLowering::getPreIndexedAddressParts(SDNode *N, SDValue &Base,
 
   SDValue Ptr;
   EVT VT;
+  unsigned Alignment;
   if (LoadSDNode *LD = dyn_cast<LoadSDNode>(N)) {
     Ptr = LD->getBasePtr();
     VT = LD->getMemoryVT();
-
+    Alignment = LD->getAlignment();
   } else if (StoreSDNode *ST = dyn_cast<StoreSDNode>(N)) {
     Ptr = ST->getBasePtr();
     VT  = ST->getMemoryVT();
+    Alignment = ST->getAlignment();
   } else
     return false;
 
@@ -1208,6 +1210,10 @@ bool PPCTargetLowering::getPreIndexedAddressParts(SDNode *N, SDValue &Base,
     if (!SelectAddressRegImm(Ptr, Offset, Base, DAG))
       return false;
   } else {
+    // LDU/STU need an address with at least 4-byte alignment.
+    if (Alignment < 4)
+      return false;
+
     // reg + imm * 4.
     if (!SelectAddressRegImmShift(Ptr, Offset, Base, DAG))
       return false;