[PATCH] [PPC64LE] Remove unnecessary swaps from lane-insensitive vector computations

[Eric Christopher]

Why is a command line option a subtarget feature? More comments inline...

-eric


REPOSITORY
  rL LLVM

================
Comment at: lib/Target/PowerPC/PPCTargetMachine.cpp:312
@@ +311,3 @@
+  TargetPassConfig::addMachineSSAOptimization();
+  if (Triple(TM->getTargetTriple()).getArch() == Triple::ppc64le)
+    addPass(createPPCVSXSwapRemovalPass());
----------------
Comment on why.

================
Comment at: lib/Target/PowerPC/PPCVSXSwapRemoval.cpp:110
@@ +109,3 @@
+  // their swap entries.  The key is the address of the MI.
+  std::map<MachineInstr*, int> SwapMap;
+
----------------
DenseMap?

================
Comment at: lib/Target/PowerPC/PPCVSXSwapRemoval.cpp:204
@@ +203,3 @@
+
+  const int InitialVectorSize(256);
+  SwapVector.clear();
----------------
256?

================
Comment at: lib/Target/PowerPC/PPCVSXSwapRemoval.cpp:251
@@ +250,3 @@
+      switch(MI->getOpcode()) {
+      default:
+        // Unless noted otherwise, an instruction is considered
----------------
What instructions not listed are you thinking here?

================
Comment at: lib/Target/PowerPC/PPCVSXSwapRemoval.cpp:614
@@ +613,3 @@
+
+        for (MachineInstr &UseMI : MRI->use_nodbg_instructions(DefReg)) {
+          int UseIdx = SwapMap[&UseMI];
----------------
Good point, what _does_ this do for debug info? :)

================
Comment at: lib/Target/PowerPC/PPCVSXSwapRemoval.cpp:646
@@ +645,3 @@
+// here.
+void PPCVSXSwapRemoval::handleSpecialSwappables(int EntryIdx) {
+}
----------------
?

http://reviews.llvm.org/D8565

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/