GlobalISel: add G_IMPLICIT_DEF instruction.

It looks like there are two target-independent but not GISel instructions that
need legalization, IMPLICIT_DEF and PHI. These are already anomalies since
their operands have important LLTs attached, so to make things more uniform it
seems like a good idea to add generic variants. Starting with G_IMPLICIT_DEF.

llvm-svn: 306875

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 121823247e1..84b0a0ac415 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -166,6 +166,20 @@ LegalizerHelper::LegalizeResult LegalizerHelper::narrowScalar(MachineInstr &MI,
   switch (MI.getOpcode()) {
   default:
     return UnableToLegalize;
+  case TargetOpcode::G_IMPLICIT_DEF: {
+    int NumParts = MRI.getType(MI.getOperand(0).getReg()).getSizeInBits() /
+                   NarrowTy.getSizeInBits();
+
+    SmallVector<unsigned, 2> DstRegs;
+    for (int i = 0; i < NumParts; ++i) {
+      unsigned Dst = MRI.createGenericVirtualRegister(NarrowTy);
+      MIRBuilder.buildUndef(Dst);
+      DstRegs.push_back(Dst);
+    }
+    MIRBuilder.buildMerge(MI.getOperand(0).getReg(), DstRegs);
+    MI.eraseFromParent();
+    return Legalized;
+  }
   case TargetOpcode::G_ADD: {
     // Expand in terms of carry-setting/consuming G_ADDE instructions.
     int NumParts = MRI.getType(MI.getOperand(0).getReg()).getSizeInBits() /