R600/SI: Implement isLegalAddressingMode

The default assumes that a 16-bit signed offset is used.
LDS instruction use a 16-bit unsigned offset, so it wasn't
being used in some cases where it was assumed a negative offset
could be used.

More should be done here, but first isLegalAddressingMode needs
to gain an addressing mode argument. For now, copy most of the rest
of the default implementation with the immediate offset change.

llvm-svn: 215732

1 files changed, 43 insertions, 0 deletions

diff --git a/llvm/lib/Target/R600/SIISelLowering.cpp b/llvm/lib/Target/R600/SIISelLowering.cpp
index f9be144461a..911c5e55949 100644
--- a/llvm/lib/Target/R600/SIISelLowering.cpp
+++ b/llvm/lib/Target/R600/SIISelLowering.cpp
@@ -242,6 +242,49 @@ SITargetLowering::SITargetLowering(TargetMachine &TM) :
 // TargetLowering queries
 //===----------------------------------------------------------------------===//
 
+// FIXME: This really needs an address space argument. The immediate offset
+// size is different for different sets of memory instruction sets.
+
+// The single offset DS instructions have a 16-bit unsigned byte offset.
+//
+// MUBUF / MTBUF have a 12-bit unsigned byte offset, and additionally can do r +
+// r + i with addr64. 32-bit has more addressing mode options. Depending on the
+// resource constant, it can also do (i64 r0) + (i32 r1) * (i14 i).
+//
+// SMRD instructions have an 8-bit, dword offset.
+//
+bool SITargetLowering::isLegalAddressingMode(const AddrMode &AM,
+                                             Type *Ty) const {
+  // No global is ever allowed as a base.
+  if (AM.BaseGV)
+    return false;
+
+  // Allow a 16-bit unsigned immediate field, since this is what DS instructions
+  // use.
+  if (!isUInt<16>(AM.BaseOffs))
+    return false;
+
+  // Only support r+r,
+  switch (AM.Scale) {
+  case 0:  // "r+i" or just "i", depending on HasBaseReg.
+    break;
+  case 1:
+    if (AM.HasBaseReg && AM.BaseOffs)  // "r+r+i" is not allowed.
+      return false;
+    // Otherwise we have r+r or r+i.
+    break;
+  case 2:
+    if (AM.HasBaseReg || AM.BaseOffs)  // 2*r+r  or  2*r+i is not allowed.
+      return false;
+    // Allow 2*r as r+r.
+    break;
+  default: // Don't allow n * r
+    return false;
+  }
+
+  return true;
+}
+
 bool SITargetLowering::allowsMisalignedMemoryAccesses(EVT  VT,
                                                       unsigned AddrSpace,
                                                       unsigned Align,