[AMDGPU] Assert if stack grows downwards. (llvm#119888)

Author: easyonaadit

llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp

@@ -1177,8 +1177,8 @@ bool AMDGPURegisterBankInfo::applyMappingDynStackAlloc(
 
   // Guard in case the stack growth direction ever changes with scratch
   // instructions.
-  if (TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown)
-    return false;
+  assert(TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsUp &&
+         "Stack grows upwards for AMDGPU");
 
   Register Dst = MI.getOperand(0).getReg();
   Register AllocSize = MI.getOperand(1).getReg();

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -4015,16 +4015,15 @@ SDValue SITargetLowering::lowerDYNAMIC_STACKALLOCImpl(
   Chain = SP.getValue(1);
   MaybeAlign Alignment = cast<ConstantSDNode>(Tmp3)->getMaybeAlignValue();
   const TargetFrameLowering *TFL = Subtarget->getFrameLowering();
-  unsigned Opc =
-    TFL->getStackGrowthDirection() == TargetFrameLowering::StackGrowsUp ?
-    ISD::ADD : ISD::SUB;
+  assert(TFL->getStackGrowthDirection() == TargetFrameLowering::StackGrowsUp &&
+         "Stack grows upwards for AMDGPU");
 
   SDValue ScaledSize = DAG.getNode(
       ISD::SHL, dl, VT, Size,
       DAG.getConstant(Subtarget->getWavefrontSizeLog2(), dl, MVT::i32));
 
   Align StackAlign = TFL->getStackAlign();
-  Tmp1 = DAG.getNode(Opc, dl, VT, SP, ScaledSize); // Value
+  Tmp1 = DAG.getNode(ISD::ADD, dl, VT, SP, ScaledSize); // Value
   if (Alignment && *Alignment > StackAlign) {
     Tmp1 = DAG.getNode(ISD::AND, dl, VT, Tmp1,
                        DAG.getConstant(-(uint64_t)Alignment->value()