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

[via llvm-commits]

================
@@ -4041,17 +4041,15 @@ SDValue SITargetLowering::lowerDYNAMIC_STACKALLOCImpl(SDValue Op,
   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
----------------
easyonaadit wrote:

Hi,
There are 2 things to consider here:
1. For AMDGPU, the Stack grows upwards (low addr to high addr)
2. The code here is based on the default implementation, which itself doesn't seem to adjust for a growing up stack.

This patch is actually just a part of fixing the logic flaw you pointed out. There is a fix in progress, you could follow it here: 
https://github.com/llvm/llvm-project/pull/119822

https://github.com/llvm/llvm-project/pull/119888