From 82b9a28c7e3e802d05c86a844804f4d87cf91fce Mon Sep 17 00:00:00 2001
From: Jessica Paquette <jpaquette@apple.com>
Date: Wed, 13 Mar 2019 23:29:54 +0000
Subject: [PATCH] [AArch64][GlobalISel] Gardening: Simplify subregister copy in
 selectBuildVector

NFC. Some more preliminary factoring for G_INSERT_VECTOR_ELT.

Also better code-reuse, etc., etc.

Differential Revision: https://reviews.llvm.org/D59323

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356107 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../AArch64/AArch64InstructionSelector.cpp    | 36 +++++++++----------
 1 file changed, 16 insertions(+), 20 deletions(-)

diff --git a/lib/Target/AArch64/AArch64InstructionSelector.cpp b/lib/Target/AArch64/AArch64InstructionSelector.cpp
index 8f3c6fd489a..b033824bfdf 100644
--- a/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -2383,28 +2383,24 @@ bool AArch64InstructionSelector::selectBuildVector(
   // If DstTy's size in bits is less than 128, then emit a subregister copy
   // from DstVec to the last register we've defined.
   if (DstSize < 128) {
-    unsigned SubReg = 0;
-
-    // Helper lambda to decide on a register class and subregister for the
-    // subregister copy.
-    auto GetRegInfoForCopy = [&SubReg,
-                              &DstSize]() -> const TargetRegisterClass * {
-      switch (DstSize) {
-      default:
-        LLVM_DEBUG(dbgs() << "Unknown destination size (" << DstSize << ")\n");
-        return nullptr;
-      case 32:
-        SubReg = AArch64::ssub;
-        return &AArch64::FPR32RegClass;
-      case 64:
-        SubReg = AArch64::dsub;
-        return &AArch64::FPR64RegClass;
-      }
-    };
-
-    const TargetRegisterClass *RC = GetRegInfoForCopy();
+    // Force this to be FPR using the destination vector.
+    const TargetRegisterClass *RC =
+        getMinClassForRegBank(*RBI.getRegBank(DstVec, MRI, TRI), DstSize);
     if (!RC)
       return false;
+    if (RC != &AArch64::FPR32RegClass && RC != &AArch64::FPR64RegClass) {
+      LLVM_DEBUG(dbgs() << "Unsupported register class!\n");
+      return false;
+    }
+
+    unsigned SubReg = 0;
+    if (!getSubRegForClass(RC, TRI, SubReg))
+      return false;
+    if (SubReg != AArch64::ssub && SubReg != AArch64::dsub) {
+      LLVM_DEBUG(dbgs() << "Unsupported destination size! (" << DstSize
+                        << "\n");
+      return false;
+    }
 
     unsigned Reg = MRI.createVirtualRegister(RC);
     unsigned DstReg = I.getOperand(0).getReg();
-- 
2.40.0