[PowerPC] Add integer truncation support to fast-isel.

This is the last substantive patch I'm planning for fast-isel in the
near future, adding fast selection of integer truncates.  There are
certainly more things that can be improved (many of which are called
out in FIXMEs), but for now we are catching most of the important
cases.

I'll document some of the remaining work in a cleanup patch shortly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189706 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/Target/PowerPC/PPCFastISel.cpp b/lib/Target/PowerPC/PPCFastISel.cpp
index 0276668e3e..0e789cc397 100644
--- a/lib/Target/PowerPC/PPCFastISel.cpp
+++ b/lib/Target/PowerPC/PPCFastISel.cpp
@@ -116,6 +116,7 @@ class PPCFastISel : public FastISel {
     bool SelectBinaryIntOp(const Instruction *I, unsigned ISDOpcode);
     bool SelectCall(const Instruction *I);
     bool SelectRet(const Instruction *I);
+    bool SelectTrunc(const Instruction *I);
     bool SelectIntExt(const Instruction *I);
 
   // Utility routines.
@@ -1667,6 +1668,34 @@ bool PPCFastISel::SelectCmp(const Instruction *I) {
   return true;
 }
 
+// Attempt to fast-select an integer truncate instruction.
+bool PPCFastISel::SelectTrunc(const Instruction *I) {
+  Value *Src  = I->getOperand(0);
+  EVT SrcVT  = TLI.getValueType(Src->getType(), true);
+  EVT DestVT = TLI.getValueType(I->getType(), true);
+
+  if (SrcVT != MVT::i64 && SrcVT != MVT::i32 && SrcVT != MVT::i16)
+    return false;
+
+  if (DestVT != MVT::i32 && DestVT != MVT::i16 && DestVT != MVT::i8)
+    return false;
+
+  unsigned SrcReg = getRegForValue(Src);
+  if (!SrcReg)
+    return false;
+
+  // The only interesting case is when we need to switch register classes.
+  if (SrcVT == MVT::i64) {
+    unsigned ResultReg = createResultReg(&PPC::GPRCRegClass);
+    BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, TII.get(TargetOpcode::COPY),
+            ResultReg).addReg(SrcReg, 0, PPC::sub_32);
+    SrcReg = ResultReg;
+  }
+
+  UpdateValueMap(I, SrcReg);
+  return true;
+}
+
 // Attempt to fast-select an integer extend instruction.
 bool PPCFastISel::SelectIntExt(const Instruction *I) {
   Type *DestTy = I->getType();
@@ -1743,6 +1772,8 @@ bool PPCFastISel::TargetSelectInstruction(const Instruction *I) {
       return SelectCall(I);
     case Instruction::Ret:
       return SelectRet(I);
+    case Instruction::Trunc:
+      return SelectTrunc(I);
     case Instruction::ZExt:
     case Instruction::SExt:
       return SelectIntExt(I);