[PowerPC] Add support for the CMPB instruction

Newer POWER cores, and the A2, support the cmpb instruction. This instruction
compares its operands, treating each of the 8 bytes in the GPRs separately,
returning a 'mask' result of 0 (for false) or -1 (for true) in each byte.

Code generation support is added, in the form of a PPCISelDAGToDAG
DAG-preprocessing routine, that recognizes patterns close to what the
instruction computes (either exactly, or related by a constant masking
operation), and generates the cmpb instruction (along with any necessary
constant masking operation). This can be expanded if use cases arise.

llvm-svn: 225106

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
index 8f0e3a49ee9..fb47c910c2f 100644
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
@@ -108,6 +108,7 @@ void PPCSubtarget::initializeEnvironment() {
   HasFPCVT = false;
   HasISEL = false;
   HasPOPCNTD = false;
+  HasCMPB = false;
   HasLDBRX = false;
   IsBookE = false;
   HasOnlyMSYNC = false;