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[AMDGPU] Handle MachineOperandType global address in SIFoldOperands. #135424

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Merged
merged 4 commits into from
May 5, 2025
Merged

[AMDGPU] Handle MachineOperandType global address in SIFoldOperands. #135424

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ea3c20a
[AMDGPU] Handle MachineOperandType global address in SIFoldOperands.
isakhilesh Apr 23, 2025
d259fb1
Patch with updated test case, based on feedback.
isakhilesh Apr 25, 2025
4f5dcb4
Updated Patch, based on feedback.
isakhilesh Apr 28, 2025
89c7ff9
fix whitespace error
arsenm May 2, 2025
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4 changes: 4 additions & 0 deletions llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
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Expand Up @@ -1161,6 +1161,10 @@ void SIFoldOperandsImpl::foldOperand(

if (OpToFold.isImm())
UseMI->getOperand(1).ChangeToImmediate(OpToFold.getImm());
else if (OpToFold.isGlobal())
UseMI->getOperand(1).ChangeToGA(OpToFold.getGlobal(),
OpToFold.getOffset(),
OpToFold.getTargetFlags());
else
UseMI->getOperand(1).ChangeToFrameIndex(OpToFold.getIndex());
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Maybe swap these? Handle isFI in the else if. We could also include explicit check for isGlobal, and give up on other operand types

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Maybe swap these? Handle isFI in the else if. We could also include explicit check for isGlobal, and give up on other operand types

Swapping isImm() and isGlobal() seems fine, if that's what you meant.

There is a UseMI->setDesc() before this conditional block, so it was not clear whether it was too late to give up because a change may have been made already?

It seemed minimum changes compared to the existing code if the existing "else" was kept untouched and a new ifGlobal() handling was added since that was the asserting case to start with.

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Yes, the setDesc would need to be sunk if the other case were handled

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@isakhilesh isakhilesh Apr 25, 2025 •
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Hi @arsenm, I had initially considered handling isFI() in else if, but as @dhruvachak mentioned, UseMI->setDesc() has potentially made changes already, so I am keeping it in the else block since there might be modifications required with respect to setDesc() as well in case we swap them.

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First, I meant do if (isImm) {} else if (isFI()) {} { else global

But you could also just move the setDesc to avoid the side effect

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I can modify the patch to the first approach you mention here. Since we enter this block only in case FoldingImmLike is true and this variable is a bool for either immediate, frame index or global values. The if-else if-else conditions focus on only these 3 operands so there won't be any edge case for the else condition as we enter the block when it is one of the 3 operands.

But I'm not clear on how/where should I move the setDesc() to, since it is almost at the top of the block and the if-else if-else is immediately after it.

The structure is ->

if(FoldingImmLike){
if(execMaybeModifiedBeforeUse)
return;
UseMI->setDesc() // at the top of the block, in case the exec flag immediately above is false
if-else if-else block
UseMI->removeOperand(2)
return;
}

Where should I place setDesc() to avoid a side effect?

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I can modify the patch to the first approach you mention here. Since we enter this block only in case FoldingImmLike is true and this variable is a bool for either immediate, frame index or global values. The if-else if-else conditions focus on only these 3 operands so there won't be any edge case for the else condition as we enter the block when it is one of the 3 operands.

But I'm not clear on how/where should I move the setDesc() to, since it is almost at the top of the block and the if-else if-else is immediately after it.

The structure is ->

if(FoldingImmLike){ if(execMaybeModifiedBeforeUse) return; UseMI->setDesc() // at the top of the block, in case the exec flag immediately above is false if-else if-else block UseMI->removeOperand(2) return; }

Where should I place setDesc() to avoid a side effect?

I think setDesc() has to be sunk only if you bail out. How about the following?

if (isImm()) {}
else if (isFI()) {}
else {
assert(isGlobal());
...
}
Then you don't need to move setDesc().

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@dhruvachak is spelling out the same as I stated

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Got it, I have updated the patch based on the suggested structure, thanks a lot. Please let me know if I can improve it further.

UseMI->removeOperand(2); // Remove exec read (or src1 for readlane)
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46 changes: 46 additions & 0 deletions llvm/test/CodeGen/AMDGPU/swdev504645-global-fold.ll
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@@ -0,0 +1,46 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
; RUN: llc -mtriple=amdgcn -mcpu=gfx942 < %s | FileCheck %s

define void @test_load_zext() {
; CHECK-LABEL: test_load_zext:
; CHECK: ; %bb.0: ; %.entry
; CHECK-NEXT: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
; CHECK-NEXT: s_mov_b32 s0, s33
; CHECK-NEXT: s_mov_b32 s33, s32
; CHECK-NEXT: s_or_saveexec_b64 s[2:3], -1
; CHECK-NEXT: scratch_store_dword off, v40, s33 ; 4-byte Folded Spill
; CHECK-NEXT: s_mov_b64 exec, s[2:3]
; CHECK-NEXT: s_add_i32 s32, s32, 16
; CHECK-NEXT: v_writelane_b32 v40, s0, 2
; CHECK-NEXT: s_getpc_b64 s[0:1]
; CHECK-NEXT: s_add_u32 s0, s0, has_spgr_args@gotpcrel32@lo+4
; CHECK-NEXT: s_addc_u32 s1, s1, has_spgr_args@gotpcrel32@hi+12
; CHECK-NEXT: s_load_dwordx2 s[2:3], s[0:1], 0x0
; CHECK-NEXT: v_writelane_b32 v40, s30, 0
; CHECK-NEXT: s_mov_b32 s0, DescriptorBuffer@abs32@lo
; CHECK-NEXT: v_writelane_b32 v40, s31, 1
; CHECK-NEXT: s_waitcnt lgkmcnt(0)
; CHECK-NEXT: s_swappc_b64 s[30:31], s[2:3]
; CHECK-NEXT: v_readlane_b32 s31, v40, 1
; CHECK-NEXT: v_readlane_b32 s30, v40, 0
; CHECK-NEXT: s_mov_b32 s32, s33
; CHECK-NEXT: v_readlane_b32 s0, v40, 2
; CHECK-NEXT: s_or_saveexec_b64 s[2:3], -1
; CHECK-NEXT: scratch_load_dword v40, off, s33 ; 4-byte Folded Reload
; CHECK-NEXT: s_mov_b64 exec, s[2:3]
; CHECK-NEXT: s_mov_b32 s33, s0
; CHECK-NEXT: s_waitcnt vmcnt(0)
; CHECK-NEXT: s_setpc_b64 s[30:31]
.entry:
%reloc = call i32 @llvm.amdgcn.reloc.constant(metadata !0)
call void @has_spgr_args(i32 %reloc)
ret void
}

declare void @has_spgr_args(i32 inreg)

declare i32 @llvm.amdgcn.reloc.constant(metadata) #0

attributes #0 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }

!0 = !{!"DescriptorBuffer", i32 4, i32 8, i32 0, i32 0}
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do we really need these attribute?

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I have removed the attribute code in line 44 but have kept the code in line 46 because without it there was an error asking for !0.
This file was reduced in llvm-reduce from an input .ll file generated by a fuzzer based on the ticket mentioned in the description.