R600/SI: Fix indirect addressing with a negative constant offset

When the base register index of the vector plus the constant offset
was less than zero, we were passing the wrong base register to the indirect
addressing instruction.

In this case, we need to set the base register to v0 and then add
the computed (negative) index to m0.

llvm-svn: 235641

1 files changed, 55 insertions, 16 deletions

diff --git a/llvm/lib/Target/R600/SILowerControlFlow.cpp b/llvm/lib/Target/R600/SILowerControlFlow.cpp
index 2e08c9f5a5d..c319b32111f 100644
--- a/llvm/lib/Target/R600/SILowerControlFlow.cpp
+++ b/llvm/lib/Target/R600/SILowerControlFlow.cpp
@@ -88,7 +88,8 @@ private:
   void Kill(MachineInstr &MI);
   void Branch(MachineInstr &MI);
 
-  void LoadM0(MachineInstr &MI, MachineInstr *MovRel);
+  void LoadM0(MachineInstr &MI, MachineInstr *MovRel, int Offset = 0);
+  void computeIndirectRegAndOffset(unsigned VecReg, unsigned &Reg, int &Offset);
   void IndirectSrc(MachineInstr &MI);
   void IndirectDst(MachineInstr &MI);
 
@@ -323,7 +324,7 @@ void SILowerControlFlowPass::Kill(MachineInstr &MI) {
   MI.eraseFromParent();
 }
 
-void SILowerControlFlowPass::LoadM0(MachineInstr &MI, MachineInstr *MovRel) {
+void SILowerControlFlowPass::LoadM0(MachineInstr &MI, MachineInstr *MovRel, int Offset) {
 
   MachineBasicBlock &MBB = *MI.getParent();
   DebugLoc DL = MI.getDebugLoc();
@@ -333,8 +334,14 @@ void SILowerControlFlowPass::LoadM0(MachineInstr &MI, MachineInstr *MovRel) {
   unsigned Idx = MI.getOperand(3).getReg();
 
   if (AMDGPU::SReg_32RegClass.contains(Idx)) {
-    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0)
-            .addReg(Idx);
+    if (Offset) {
+      BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_ADD_I32), AMDGPU::M0)
+              .addReg(Idx)
+              .addImm(Offset);
+    } else {
+      BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0)
+              .addReg(Idx);
+    }
     MBB.insert(I, MovRel);
   } else {
 
@@ -363,6 +370,11 @@ void SILowerControlFlowPass::LoadM0(MachineInstr &MI, MachineInstr *MovRel) {
     BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_AND_SAVEEXEC_B64), AMDGPU::VCC)
             .addReg(AMDGPU::VCC);
 
+    if (Offset) {
+      BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_ADD_I32), AMDGPU::M0)
+              .addReg(AMDGPU::M0)
+              .addImm(Offset);
+    }
     // Do the actual move
     MBB.insert(I, MovRel);
 
@@ -384,6 +396,33 @@ void SILowerControlFlowPass::LoadM0(MachineInstr &MI, MachineInstr *MovRel) {
   MI.eraseFromParent();
 }
 
+/// \param @VecReg The register which holds element zero of the vector
+///                 being addressed into.
+/// \param[out] @Reg The base register to use in the indirect addressing instruction.
+/// \param[in,out] @Offset As an input, this is the constant offset part of the
+//                         indirect Index. e.g. v0 = v[VecReg + Offset]
+//                         As an output, this is a constant value that needs
+//                         to be added to the value stored in M0.
+void SILowerControlFlowPass::computeIndirectRegAndOffset(unsigned VecReg,
+                                                         unsigned &Reg,
+                                                         int &Offset) {
+  unsigned SubReg = TRI->getSubReg(VecReg, AMDGPU::sub0);
+  if (!SubReg)
+    SubReg = VecReg;
+
+  const TargetRegisterClass *RC = TRI->getPhysRegClass(SubReg);
+  int RegIdx = TRI->getHWRegIndex(SubReg) + Offset;
+
+  if (RegIdx < 0) {
+    Offset = RegIdx;
+    RegIdx = 0;
+  } else {
+    Offset = 0;
+  }
+
+  Reg = RC->getRegister(RegIdx);
+}
+
 void SILowerControlFlowPass::IndirectSrc(MachineInstr &MI) {
 
   MachineBasicBlock &MBB = *MI.getParent();
@@ -391,18 +430,18 @@ void SILowerControlFlowPass::IndirectSrc(MachineInstr &MI) {
 
   unsigned Dst = MI.getOperand(0).getReg();
   unsigned Vec = MI.getOperand(2).getReg();
-  unsigned Off = MI.getOperand(4).getImm();
-  unsigned SubReg = TRI->getSubReg(Vec, AMDGPU::sub0);
-  if (!SubReg)
-    SubReg = Vec;
+  int Off = MI.getOperand(4).getImm();
+  unsigned Reg;
+
+  computeIndirectRegAndOffset(Vec, Reg, Off);
 
   MachineInstr *MovRel =
     BuildMI(*MBB.getParent(), DL, TII->get(AMDGPU::V_MOVRELS_B32_e32), Dst)
-            .addReg(SubReg + Off)
+            .addReg(Reg)
             .addReg(AMDGPU::M0, RegState::Implicit)
             .addReg(Vec, RegState::Implicit);
 
-  LoadM0(MI, MovRel);
+  LoadM0(MI, MovRel, Off);
 }
 
 void SILowerControlFlowPass::IndirectDst(MachineInstr &MI) {
@@ -411,20 +450,20 @@ void SILowerControlFlowPass::IndirectDst(MachineInstr &MI) {
   DebugLoc DL = MI.getDebugLoc();
 
   unsigned Dst = MI.getOperand(0).getReg();
-  unsigned Off = MI.getOperand(4).getImm();
+  int Off = MI.getOperand(4).getImm();
   unsigned Val = MI.getOperand(5).getReg();
-  unsigned SubReg = TRI->getSubReg(Dst, AMDGPU::sub0);
-  if (!SubReg)
-    SubReg = Dst;
+  unsigned Reg;
+
+  computeIndirectRegAndOffset(Dst, Reg, Off);
 
   MachineInstr *MovRel = 
     BuildMI(*MBB.getParent(), DL, TII->get(AMDGPU::V_MOVRELD_B32_e32))
-            .addReg(SubReg + Off, RegState::Define)
+            .addReg(Reg, RegState::Define)
             .addReg(Val)
             .addReg(AMDGPU::M0, RegState::Implicit)
             .addReg(Dst, RegState::Implicit);
 
-  LoadM0(MI, MovRel);
+  LoadM0(MI, MovRel, Off);
 }
 
 bool SILowerControlFlowPass::runOnMachineFunction(MachineFunction &MF) {