bpf: New target attribute "alu32" for 32-bit subregister support

This new attribute aims to control the enablement of 32-bit subregister
support on eBPF backend.

Name the interface as "alu32" is because we in particular want to enable
the generation of BPF_ALU32 instructions by enable subregister support.

This attribute could be used in the following format with llc:

  llc -mtriple=bpf -mattr=[+|-]alu32

It is disabled at default.

Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Yonghong Song <yhs@fb.com>
llvm-svn: 325982

3 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/BPF/BPF.td b/llvm/lib/Target/BPF/BPF.td
index 2d0c22a3a51..b8c2298584c 100644
--- a/llvm/lib/Target/BPF/BPF.td
+++ b/llvm/lib/Target/BPF/BPF.td
@@ -26,6 +26,9 @@ def : Proc<"probe", []>;
 def DummyFeature : SubtargetFeature<"dummy", "isDummyMode",
                                     "true", "unused feature">;
 
+def ALU32 : SubtargetFeature<"alu32", "HasAlu32", "true",
+                             "Enable ALU32 instructions">;
+
 def BPFInstPrinter : AsmWriter {
   string AsmWriterClassName  = "InstPrinter";
   bit isMCAsmWriter = 1;
diff --git a/llvm/lib/Target/BPF/BPFSubtarget.cpp b/llvm/lib/Target/BPF/BPFSubtarget.cpp
index 42ca87f9ef6..2bb07032304 100644
--- a/llvm/lib/Target/BPF/BPFSubtarget.cpp
+++ b/llvm/lib/Target/BPF/BPFSubtarget.cpp
@@ -30,11 +30,13 @@ BPFSubtarget &BPFSubtarget::initializeSubtargetDependencies(StringRef CPU,
                                                             StringRef FS) {
   initializeEnvironment();
   initSubtargetFeatures(CPU, FS);
+  ParseSubtargetFeatures(CPU, FS);
   return *this;
 }
 
 void BPFSubtarget::initializeEnvironment() {
   HasJmpExt = false;
+  HasAlu32 = false;
 }
 
 void BPFSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
diff --git a/llvm/lib/Target/BPF/BPFSubtarget.h b/llvm/lib/Target/BPF/BPFSubtarget.h
index fa1f24443bc..4fbd4b00181 100644
--- a/llvm/lib/Target/BPF/BPFSubtarget.h
+++ b/llvm/lib/Target/BPF/BPFSubtarget.h
@@ -47,6 +47,9 @@ protected:
   // whether the cpu supports jmp ext
   bool HasJmpExt;
 
+  // whether the cpu supports alu32 instructions.
+  bool HasAlu32;
+
 public:
   // This constructor initializes the data members to match that
   // of the specified triple.
@@ -59,6 +62,7 @@ public:
   // subtarget options.  Definition of function is auto generated by tblgen.
   void ParseSubtargetFeatures(StringRef CPU, StringRef FS);
   bool getHasJmpExt() const { return HasJmpExt; }
+  bool getHasAlu32() const { return HasAlu32; }
 
   const BPFInstrInfo *getInstrInfo() const override { return &InstrInfo; }
   const BPFFrameLowering *getFrameLowering() const override {