[PowerPC] Implement readcyclecounter for PPC32

We've long supported readcyclecounter on PPC64, but it is easier there (the
read of the 64-bit time-base register can be accomplished via a single
instruction). This now provides an implementation for PPC32 as well. On PPC32,
the time-base register is still 64 bits, but can only be read 32 bits at a time
via two separate SPRs. The ISA manual explains how to do this properly (it
involves re-reading the upper bits and looping if the counter has wrapped while
being read).

This requires PPC to implement a custom integer splitting legalization for the
READCYCLECOUNTER node, turning it into a target-specific SDAG node, which then
gets turned into a pseudo-instruction, which is then expanded to the necessary
sequence (which has three SPR reads, the comparison and the branch).

Thanks to Paul Hargrove for pointing out to me that this was still unimplemented.

llvm-svn: 223161

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
index bd7dacf2bc6..ebf6b28259e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
@@ -921,6 +921,17 @@ bool DAGTypeLegalizer::CustomLowerNode(SDNode *N, EVT VT, bool LegalizeResult) {
     // The target didn't want to custom lower it after all.
     return false;
 
+  // When called from DAGTypeLegalizer::ExpandIntegerResult, we might need to
+  // provide the same kind of custom splitting behavior.
+  if (Results.size() == N->getNumValues() + 1 && LegalizeResult) {
+    // We've legalized a return type by splitting it. If there is a chain,
+    // replace that too.
+    SetExpandedInteger(SDValue(N, 0), Results[0], Results[1]);
+    if (N->getNumValues() > 1)
+      ReplaceValueWith(SDValue(N, 1), Results[2]);
+    return true;
+  }
+
   // Make everything that once used N's values now use those in Results instead.
   assert(Results.size() == N->getNumValues() &&
          "Custom lowering returned the wrong number of results!");