[AMDGPU] Fix Livereg computation during epilogue insertion

The LivePhysRegs calculated in order to find a scratch register in the
epilogue code wrongly uses 'LiveIns'. Instead, it should use the
'Liveout' sets.  For the liveness, also considering the operands of
the terminator (return) instruction which is the insertion point for
the scratch-exec-copy instruction.

Patch by Christudasan Devadasan

llvm-svn: 364470

2 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp b/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
index 098152b23aa..3ed6d75c045 100644
--- a/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
@@ -678,7 +678,8 @@ void SIFrameLowering::emitEpilogue(MachineFunction &MF,
     if (ScratchExecCopy == AMDGPU::NoRegister) {
       // See emitPrologue
       LivePhysRegs LiveRegs(*ST.getRegisterInfo());
-      LiveRegs.addLiveIns(MBB);
+      LiveRegs.addLiveOuts(MBB);
+      LiveRegs.stepBackward(*MBBI);
 
       ScratchExecCopy
         = findScratchNonCalleeSaveRegister(MF, LiveRegs,
diff --git a/llvm/test/CodeGen/AMDGPU/callee-special-input-sgprs.ll b/llvm/test/CodeGen/AMDGPU/callee-special-input-sgprs.ll
index 5368eb20300..ba099c33fc2 100644
--- a/llvm/test/CodeGen/AMDGPU/callee-special-input-sgprs.ll
+++ b/llvm/test/CodeGen/AMDGPU/callee-special-input-sgprs.ll
@@ -489,6 +489,7 @@ define amdgpu_kernel void @kern_indirect_use_every_sgpr_input() #1 {
 ; GCN-NOT: s[8:9]
 ; GCN-NOT: s[10:11]
 ; GCN-NOT: s[12:13]
+; GCN: s_or_saveexec_b64 s[6:7], -1
 define hidden void @func_indirect_use_every_sgpr_input() #1 {
   call void @use_every_sgpr_input()
   ret void