[llvm] [SPIRV] Implement translation for llvm.modf.* intrinsics (PR #147556)

[Victor Lomuller via llvm-commits]

================
@@ -995,4 +995,26 @@ unsigned getArrayComponentCount(const MachineRegisterInfo *MRI,
   return foldImm(ResType->getOperand(2), MRI);
 }
 
+MachineBasicBlock::iterator
+getPosForOpVariableWithinBlock(MachineBasicBlock &BB) {
+  // Find the position to insert the OpVariable instruction.
+  // We will insert it after the last OpFunctionParameter, if any, or
+  // after OpFunction otherwise.
+  MachineBasicBlock::iterator VarPos = BB.begin();
+  while (VarPos != BB.end() && VarPos->getOpcode() != SPIRV::OpFunction) {
+    ++VarPos;
+  }
+  // Advance VarPos to the next instruction after OpFunction, it will either
+  // be an OpFunctionParameter, so that we can start the next loop, or the
+  // position to insert the OpVariable instruction.
+  ++VarPos;
+  while (VarPos != BB.end() &&
+         VarPos->getOpcode() == SPIRV::OpFunctionParameter) {
+    ++VarPos;
+  }
+  // VarPos is now pointing at after the last OpFunctionParameter, if any,
+  // or after OpFunction, if no parameters.
+  return VarPos;
----------------
Naghasan wrote:

```suggestion
  return VarPos != BB.end() && VarPos->getOpcode() == SPIRV::OpLabel ? ++VarPos : VarPos;
```

https://github.com/llvm/llvm-project/pull/147556