AMDGPU/GlobalISel: Allow VGPR to index SGPR register

We can still do a waterfall loop over the index if using a VGPR to
index an SGPR. The result will still be a VGPR, but we can avoid the
wide copy of the source register to a VGPR.

llvm-svn: 373637

1 files changed, 6 insertions, 4 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
index 8aa296b1132..f8ea17d7f3f 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
@@ -2309,14 +2309,16 @@ AMDGPURegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
     break;
   }
   case AMDGPU::G_EXTRACT_VECTOR_ELT: {
-    unsigned OutputBankID = isSALUMapping(MI) ?
-                            AMDGPU::SGPRRegBankID : AMDGPU::VGPRRegBankID;
+    // VGPR index can be used for waterfall when indexing a SGPR vector.
+    unsigned SrcBankID = getRegBankID(MI.getOperand(1).getReg(), MRI, *TRI);
+    unsigned DstSize = MRI.getType(MI.getOperand(0).getReg()).getSizeInBits();
     unsigned SrcSize = MRI.getType(MI.getOperand(1).getReg()).getSizeInBits();
     unsigned IdxSize = MRI.getType(MI.getOperand(2).getReg()).getSizeInBits();
     unsigned IdxBank = getRegBankID(MI.getOperand(2).getReg(), MRI, *TRI);
+    unsigned OutputBankID = regBankUnion(SrcBankID, IdxBank);
 
-    OpdsMapping[0] = AMDGPU::getValueMapping(OutputBankID, SrcSize);
-    OpdsMapping[1] = AMDGPU::getValueMapping(OutputBankID, SrcSize);
+    OpdsMapping[0] = AMDGPU::getValueMapping(OutputBankID, DstSize);
+    OpdsMapping[1] = AMDGPU::getValueMapping(SrcBankID, SrcSize);
 
     // The index can be either if the source vector is VGPR.
     OpdsMapping[2] = AMDGPU::getValueMapping(IdxBank, IdxSize);