[MIPS GlobalISel] NarrowScalar G_TRUNC

Add NarrowScalar for G_TRUNC when NarrowTy is half the size of source.
NarrowScalar G_TRUNC to s32 for MIPS32.

Differential Revision: https://reviews.llvm.org/D66202

llvm-svn: 369509

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 26c25ba26d4..4622248102e 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -633,6 +633,21 @@ LegalizerHelper::LegalizeResult LegalizerHelper::narrowScalar(MachineInstr &MI,
     MI.eraseFromParent();
     return Legalized;
   }
+  case TargetOpcode::G_TRUNC: {
+    if (TypeIdx != 1)
+      return UnableToLegalize;
+
+    uint64_t SizeOp1 = MRI.getType(MI.getOperand(1).getReg()).getSizeInBits();
+    if (NarrowTy.getSizeInBits() * 2 != SizeOp1) {
+      LLVM_DEBUG(dbgs() << "Can't narrow trunc to type " << NarrowTy << "\n");
+      return UnableToLegalize;
+    }
+
+    auto Unmerge = MIRBuilder.buildUnmerge(NarrowTy, MI.getOperand(1).getReg());
+    MIRBuilder.buildCopy(MI.getOperand(0).getReg(), Unmerge.getReg(0));
+    MI.eraseFromParent();
+    return Legalized;
+  }
 
   case TargetOpcode::G_ADD: {
     // FIXME: add support for when SizeOp0 isn't an exact multiple of