AMDGPU/SI: Make sure MIMG descriptors and samplers stay in SGPRs

Summary:
It's possible to have resource descriptors and samplers stored in
VGPRs, either by a VMEM instruction or in the case of samplers,
floating-point calculations.  When this happens, we need to use
v_readfirstlane to copy these values back to sgprs.

Reviewers: mareko, arsenm

Subscribers: arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D17102

llvm-svn: 260599

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.h b/llvm/lib/Target/AMDGPU/SIInstrInfo.h
index c2d51a56d5c..66e80c3f272 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.h
@@ -396,6 +396,13 @@ public:
   /// \brief Fix operands in \p MI to satisfy constant bus requirements.
   void legalizeOperandsVOP3(MachineRegisterInfo &MRI, MachineInstr *MI) const;
 
+  /// Copy a value from a VGPR (\p SrcReg) to SGPR.  This function can only
+  /// be used when it is know that the value in SrcReg is same across all
+  /// threads in the wave.
+  /// \returns The SGPR register that \p SrcReg was copied to.
+  unsigned readlaneVGPRToSGPR(unsigned SrcReg, MachineInstr *UseMI,
+                          MachineRegisterInfo &MRI) const;
+
   /// \brief Legalize all operands in this instruction.  This function may
   /// create new instruction and insert them before \p MI.
   void legalizeOperands(MachineInstr *MI) const;