commit 936483fb7dd2c8c6b014516ff3b3cd13740e0518
author Matt Arsenault <Matthew.Arsenault@amd.com> Thu Jan 09 21:53:28 2020 -0500
committer Matt Arsenault <arsenm2@gmail.com> Wed Jan 15 08:58:58 2020 -0500
tree ab7dd66c7c654b2dbbb9d119533506402d581f50
parent bd7658a212ebc27a8f7d69666820df33bc8d61f5

GlobalISel: Implement lower for G_BITCAST

Bitcast only really applies between scalars and vectors. Implement as
an unmerge and remerge. The test needs to tolerate failure since one
of the unmerges currently fails to legalize.

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 5588acd..8a26703 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -1941,6 +1941,39 @@
   }
 }
 
+static void getUnmergePieces(SmallVectorImpl<Register> &Pieces,
+                             MachineIRBuilder &B, Register Src, LLT Ty) {
+  auto Unmerge = B.buildUnmerge(Ty, Src);
+  for (int I = 0, E = Unmerge->getNumOperands() - 1; I != E; ++I)
+    Pieces.push_back(Unmerge.getReg(I));
+}
+
+LegalizerHelper::LegalizeResult
+LegalizerHelper::lowerBitcast(MachineInstr &MI) {
+  Register Dst = MI.getOperand(0).getReg();
+  Register Src = MI.getOperand(1).getReg();
+  LLT DstTy = MRI.getType(Dst);
+  LLT SrcTy = MRI.getType(Src);
+
+  if (SrcTy.isVector() && !DstTy.isVector()) {
+    SmallVector<Register, 8> SrcRegs;
+    getUnmergePieces(SrcRegs, MIRBuilder, Src, SrcTy.getElementType());
+    MIRBuilder.buildMerge(Dst, SrcRegs);
+    MI.eraseFromParent();
+    return Legalized;
+  }
+
+  if (DstTy.isVector() && !SrcTy.isVector()) {
+    SmallVector<Register, 8> SrcRegs;
+    getUnmergePieces(SrcRegs, MIRBuilder, Src, DstTy.getElementType());
+    MIRBuilder.buildMerge(Dst, SrcRegs);
+    MI.eraseFromParent();
+    return Legalized;
+  }
+
+  return UnableToLegalize;
+}
+
 LegalizerHelper::LegalizeResult
 LegalizerHelper::lower(MachineInstr &MI, unsigned TypeIdx, LLT Ty) {
   using namespace TargetOpcode;
@@ -1949,6 +1982,8 @@
   switch(MI.getOpcode()) {
   default:
     return UnableToLegalize;
+  case TargetOpcode::G_BITCAST:
+    return lowerBitcast(MI);
   case TargetOpcode::G_SREM:
   case TargetOpcode::G_UREM: {
     Register QuotReg = MRI.createGenericVirtualRegister(Ty);