[AMDGPU] Assert if stack grows downwards. #119888
Conversation
|
Thank you for submitting a Pull Request (PR) to the LLVM Project! This PR will be automatically labeled and the relevant teams will be notified. If you wish to, you can add reviewers by using the "Reviewers" section on this page. If this is not working for you, it is probably because you do not have write permissions for the repository. In which case you can instead tag reviewers by name in a comment by using If you have received no comments on your PR for a week, you can request a review by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate is once a week. Please remember that you are asking for valuable time from other developers. If you have further questions, they may be answered by the LLVM GitHub User Guide. You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums. |
|
@llvm/pr-subscribers-backend-amdgpu Author: Aaditya (easyonaadit) ChangesFull diff: https://github.com/llvm/llvm-project/pull/119888.diff 2 Files Affected:
diff --git a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
index e5baffc0f064b2..72c3e4a64c18bc 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
@@ -1181,8 +1181,8 @@ 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\n");
Register Dst = MI.getOperand(0).getReg();
Register AllocSize = MI.getOperand(1).getReg();
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 8dfebd36a962e1..9366cb31640f9b 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -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\n");
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,
|
cdevadas
changed the title
|
@easyonaadit Congratulations on having your first Pull Request (PR) merged into the LLVM Project! Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR. Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues. How to do this, and the rest of the post-merge process, is covered in detail here. If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again. If you don't get any reports, no action is required from you. Your changes are working as expected, well done! |
|
|
||
| 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 |
There was a problem hiding this comment.
(not related to this PR, but I thought it was worth reporting)
If I'm reading correctly, the logic is broken for the case when the object alignment is greater than the stack alignment.
The ISD::AND below may result in an address that points below the current SP, possibly into a previously allocated object.
Consider: SP = 40, StackAlign = 8, ScaledSize = 16, (Scaled)Alignment = 32
Tmp1 = ADD 40, 16 = 56
Tmp1 = AND 56, -32 = 32
The new address (32) is less than the previous value of the stack pointer (40).
ADD
And the returned address (Tmp1) points past the allocated object. Probably I don't understand something...
There was a problem hiding this comment.
Hi,
There are 2 things to consider here:
- For AMDGPU, the Stack grows upwards (low addr to high addr)
- 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:
#119822
There was a problem hiding this comment.
The default implementation is dead code for StackGrowsUp. I was going to fix it, but I couldn't add tests for the changes.
There was a problem hiding this comment.
Other than scaling for wave size, the code changes in #119822 serve as a generic implementation for a growing up stack. And there are test cases along with it as well. Could this be replicated?
There was a problem hiding this comment.
The only other target that uses positive stack growth is NVPTX
No description provided.