AMDGPU: Remove unnecessary check for constant operands

[arsenm]

Summary

An instruction that has an immediate operand can't reach
this point. This is only called for a freshly shrunk instruction,
which prevously couldn't have had a literal constant operand.
This was also not conservative enough since it woudl also have
had to filter other constant-like inputs like frame indexes.

[rampitec]

LGTM

[arsenm]

r307574

lib/Target/AMDGPU/SIShrinkInstructions.cpp

static void foldImmediates(MachineInstr &MI, const SIInstrInfo *TII,
 
   if (!MRI.isSSA())
     return;
 
   assert(TII->isVOP1(MI) || TII->isVOP2(MI) || TII->isVOPC(MI));
 
   int Src0Idx = AMDGPU::getNamedOperandIdx(MI.getOpcode(), AMDGPU::OpName::src0);
 
-  // Only one literal constant is allowed per instruction, so if src0 is a
-  // literal constant then we can't do any folding.
-  if (TII->isLiteralConstant(MI, Src0Idx))
-    return;
-
   // Try to fold Src0
   MachineOperand &Src0 = MI.getOperand(Src0Idx);
   if (Src0.isReg() && MRI.hasOneUse(Src0.getReg())) {
     unsigned Reg = Src0.getReg();
     MachineInstr *Def = MRI.getUniqueVRegDef(Reg);
     if (Def && Def->isMoveImmediate()) {
       MachineOperand &MovSrc = Def->getOperand(1);
       bool ConstantFolded = false;