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[AMDGPU] update LDS block size for gfx1250 #167614

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[AMDGPU] update LDS block size for gfx1250 #167614

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97f6ccd
[AMDGPU] update LDS block size for gfx1250
changpeng Nov 12, 2025
b9844d9
Update AMDGPU::getLdsDwGranularity
changpeng Nov 12, 2025
c17c39c
Update maximum lds size for hsa-gfx125*-v4.s
changpeng Nov 13, 2025
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2 changes: 1 addition & 1 deletion llvm/docs/AMDGPUUsage.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -5855,7 +5855,7 @@ The fields used by CP for code objects before V3 also match those specified in
GFX950
roundup(lds-size / (320 * 4))
GFX125*
roundup(lds-size / (256 * 4))
roundup(lds-size / (512 * 4))

24 1 bit ENABLE_EXCEPTION_IEEE_754_FP Wavefront starts execution
_INVALID_OPERATION with specified exceptions
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9 changes: 3 additions & 6 deletions llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
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Expand Up @@ -1161,12 +1161,9 @@ void AMDGPUAsmPrinter::getSIProgramInfo(SIProgramInfo &ProgInfo,
ProgInfo.DX10Clamp = Mode.DX10Clamp;

unsigned LDSAlignShift;
if (STM.getFeatureBits().test(FeatureAddressableLocalMemorySize327680)) {
// LDS is allocated in 256 dword blocks.
LDSAlignShift = 10;
} else if (STM.getFeatureBits().test(
FeatureAddressableLocalMemorySize163840)) {
// LDS is allocated in 320 dword blocks.
if (STM.getFeatureBits().test(FeatureAddressableLocalMemorySize327680) ||
STM.getFeatureBits().test(FeatureAddressableLocalMemorySize163840)) {
Comment on lines +1164 to +1165
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@arsenm arsenm Nov 12, 2025

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Seems like this should be modeled more directly rather than inferring the allocation size by the target that supports this allocation size

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@changpeng changpeng Nov 12, 2025

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Seems like this should be modeled more directly rather than inferring the allocation size by the target that supports this allocation size

Do you mean something directly like?:
if (gfx1250)
LDSAlignShift = 11;

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@changpeng changpeng Nov 12, 2025 •
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@arsenm : should we get the lds block size from the target directly?

// LDS is allocated in 512 or 320 dword blocks.
LDSAlignShift = 11;
} else if (STM.getFeatureBits().test(
FeatureAddressableLocalMemorySize65536)) {
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2 changes: 1 addition & 1 deletion llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp
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Expand Up @@ -3546,7 +3546,7 @@ bool isDPALU_DPP(const MCInstrDesc &OpDesc, const MCInstrInfo &MII,
}

unsigned getLdsDwGranularity(const MCSubtargetInfo &ST) {
return ST.hasFeature(AMDGPU::FeatureAddressableLocalMemorySize327680) ? 256
return ST.hasFeature(AMDGPU::FeatureAddressableLocalMemorySize327680) ? 512
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@rampitec rampitec Nov 13, 2025

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That becomes more and more strange, doc lists other sizes, but here we have only 2.

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@changpeng changpeng Nov 13, 2025

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That becomes more and more strange, doc lists other sizes, but here we have only 2.
Maybe it is missing for gfx950 (320 byte block),
And R600 was possibly missed intentionally.
We should add them, also call AMDGPU::getLdsDwGranularity in AMDGPUAsmPrinter::getSIProgramInfo too.

But this needs additional investigation and LIT tests, and should fall into separate PRs, I think.

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@rampitec rampitec Nov 13, 2025

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Perhaps. But I'd still expect hsa-gfx1250-v4.s to show some changes.

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@changpeng changpeng Nov 13, 2025

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Perhaps. But I'd still expect hsa-gfx1250-v4.s to show some changes.

Do you mean we need to add additional tests to expose the change, or something is missed updating when we change the LDS block size in this PR? Thanks; ( I will change the maximum lds size in the test though)

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@rampitec rampitec Nov 13, 2025

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Probably some other place is not changed. Try changing max size in the test, I'd assume hex dump will change.

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@changpeng changpeng Nov 13, 2025

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Probably some other place is not changed. Try changing max size in the test, I'd assume hex dump will change.

maximum lds size updated, and the hex dump changes accordingly. I am going to double check what we possibly missed. Thanks.

: 128;
}

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4 changes: 2 additions & 2 deletions llvm/test/CodeGen/AMDGPU/extra-lds-size.ll
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Expand Up @@ -31,10 +31,10 @@
; GFX1200-MESA: .long 45100
; GFX1200-MESA-NEXT: .long 1024

; GFX1250-PAL: '0x2c0b (SPI_SHADER_PGM_RSRC2_PS)': 0x200
; GFX1250-PAL: '0x2c0b (SPI_SHADER_PGM_RSRC2_PS)': 0x100
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@arsenm arsenm Nov 12, 2025

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Not sure how this test ends up showing the allocation granularity


; GFX1250-MESA: .long 45100
; GFX1250-MESA-NEXT: .long 512
; GFX1250-MESA-NEXT: .long 256

@lds = internal addrspace(3) global [4096 x i8] poison

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6 changes: 3 additions & 3 deletions llvm/test/CodeGen/AMDGPU/lds-size-hsa-gfx1250.ll
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Expand Up @@ -41,7 +41,7 @@ define amdgpu_kernel void @test_lds_i32(i32 %val) {
; GCN-LABEL: test_lds_array_i8:
; GCN: .amdhsa_group_segment_fixed_size 327680
; GCN: ; LDSByteSize: 327680 bytes/workgroup
; MESA: granulated_lds_size = 320
; MESA: granulated_lds_size = 160
define amdgpu_kernel void @test_lds_array_i8() {
%gep = getelementptr inbounds [327679 x i8], ptr addrspace(3) @lds.array.i8, i32 0, i32 5
%val = load i8, ptr addrspace(3) %gep
Expand All @@ -52,7 +52,7 @@ define amdgpu_kernel void @test_lds_array_i8() {
; GCN-LABEL: test_lds_array_i16:
; GCN: .amdhsa_group_segment_fixed_size 327680
; GCN: ; LDSByteSize: 327680 bytes/workgroup
; MESA: granulated_lds_size = 320
; MESA: granulated_lds_size = 160
define amdgpu_kernel void @test_lds_array_i16() {
%gep = getelementptr inbounds [163839 x i16], ptr addrspace(3) @lds.array.i16, i32 0, i32 10
%val = load i16, ptr addrspace(3) %gep
Expand All @@ -63,7 +63,7 @@ define amdgpu_kernel void @test_lds_array_i16() {
; GCN-LABEL: test_lds_array_i32:
; GCN: .amdhsa_group_segment_fixed_size 327680
; GCN: ; LDSByteSize: 327680 bytes/workgroup
; MESA: granulated_lds_size = 320
; MESA: granulated_lds_size = 160
define amdgpu_kernel void @test_lds_array_i32() {
%gep = getelementptr inbounds [81919 x i32], ptr addrspace(3) @lds.array.i32, i32 0, i32 20
%val = load i32, ptr addrspace(3) %gep
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2 changes: 1 addition & 1 deletion llvm/test/CodeGen/AMDGPU/pal-metadata-3.0.gfx1250.ll
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Expand Up @@ -114,7 +114,7 @@
; CHECK-NEXT: .entry_point: _amdgpu_gs
; CHECK-NEXT: .entry_point_symbol: gs_shader
; CHECK-NEXT: .forward_progress: true
; CHECK-NEXT: .lds_size: 0x400
; CHECK-NEXT: .lds_size: 0x800
; CHECK-NEXT: .mem_ordered: true
; CHECK-NEXT: .scratch_en: false
; CHECK-NEXT: .scratch_memory_size: 0
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