[llvm-branch-commits] [llvm] AMDGPU: Fix fixme for out of bounds indexing in usesConstantBus check (PR #155603)

[Stanislav Mekhanoshin via llvm-branch-commits]

================
@@ -4758,30 +4758,45 @@ MachineInstr *SIInstrInfo::buildShrunkInst(MachineInstr &MI,
   return Inst32;
 }
 
+bool SIInstrInfo::physRegUsesConstantBus(const MachineOperand &RegOp) const {
+  // Null is free
+  Register Reg = RegOp.getReg();
+  if (Reg == AMDGPU::SGPR_NULL || Reg == AMDGPU::SGPR_NULL64)
+    return false;
+
+  // SGPRs use the constant bus
+
+  // FIXME: implicit registers that are not part of the MCInstrDesc's implicit
+  // physical register operands should also count.
+  if (RegOp.isImplicit())
+    return Reg == AMDGPU::VCC || Reg == AMDGPU::VCC_LO || Reg == AMDGPU::M0;
+
+  // Normal exec read does not count.
+  if ((Reg == AMDGPU::EXEC || Reg == AMDGPU::EXEC_LO) && RegOp.isImplicit())
+    return false;
+
+  // SGPRs use the constant bus
+  return AMDGPU::SReg_32RegClass.contains(Reg) ||
----------------
rampitec wrote:

`isSGPRPhysReg()`? Just in case we will have more classes, or got ttmp or something like that in the future.

https://github.com/llvm/llvm-project/pull/155603