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[DirectX] Implement UseNativeLowPrecision shader flag analysis #134288

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Merged
merged 8 commits into from
Apr 10, 2025
Merged

[DirectX] Implement UseNativeLowPrecision shader flag analysis #134288

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c482c96
Add test for UseNativeLowPrecision shader flag
Icohedron Apr 2, 2025
1d90753
Implement UseNativeLowPrecision shader flag analysis
Icohedron Apr 3, 2025
33f5896
Add check for DXIL Version >= 1.2
Icohedron Apr 3, 2025
5656192
Apply clang-format
Icohedron Apr 3, 2025
35a0804
Replace clang_cc1 with clang_dxc in enable-16bit-types test
Icohedron Apr 8, 2025
09864cf
Remove unnecessary attributes and obj2yml test
Icohedron Apr 8, 2025
0e8b7fa
Add a comment describing the purpose of the NativeHalfType conditional
Icohedron Apr 8, 2025
71687e4
Add '-Xclang -emit-llvm' to avoid running the DirectX backend
Icohedron Apr 9, 2025
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4 changes: 4 additions & 0 deletions clang/lib/CodeGen/CGHLSLRuntime.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -282,10 +282,14 @@ void CGHLSLRuntime::addHLSLBufferLayoutType(const RecordType *StructType,

void CGHLSLRuntime::finishCodeGen() {
auto &TargetOpts = CGM.getTarget().getTargetOpts();
auto &LangOpts = CGM.getLangOpts();
llvm::Module &M = CGM.getModule();
Triple T(M.getTargetTriple());
if (T.getArch() == Triple::ArchType::dxil)
addDxilValVersion(TargetOpts.DxilValidatorVersion, M);
if (LangOpts.NativeHalfType)
M.setModuleFlag(llvm::Module::ModFlagBehavior::Error, "dx.nativelowprec",
1);

generateGlobalCtorDtorCalls();
}
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9 changes: 9 additions & 0 deletions clang/test/CodeGenHLSL/enable-16bit-types.hlsl
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@@ -0,0 +1,9 @@
// RUN: %clang_cc1 -fnative-half-type -finclude-default-header -triple dxil-pc-shadermodel6.3-library -emit-llvm -disable-llvm-passes -o - %s | FileCheck %s --check-prefix=FLAG
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NIT: For future cleanup and test organization could we move the Shader Flag tests into their own directory like the Builtins have their own directory? Not asking for this PR.

// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.3-library -emit-llvm -disable-llvm-passes -o - %s | FileCheck %s --check-prefix=NOFLAG

// NOTE: -enable-16bit-types is a DXCFlag that aliases -fnative-half-type

// FLAG-DAG: ![[NLP:.*]] = !{i32 1, !"dx.nativelowprec", i32 1}
// FLAG-DAG: !llvm.module.flags = !{{{.*}}![[NLP]]{{.*}}}

// NOFLAG-NOT: dx.nativelowprec
7 changes: 7 additions & 0 deletions llvm/lib/Target/DirectX/DXILShaderFlags.cpp
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Expand Up @@ -188,6 +188,13 @@ void ModuleShaderFlags::initialize(Module &M, DXILResourceTypeMap &DRTM,
continue;
}

// Set UseNativeLowPrecision using dx.nativelowprec module metadata
if (auto *NativeLowPrec = mdconst::extract_or_null<ConstantInt>(
M.getModuleFlag("dx.nativelowprec")))
if (MMDI.DXILVersion >= VersionTuple(1, 2) &&
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So I know the frontend likely has checks to confirm SM 6.2 or greater for this flag. If the backend is dxil-pc-shadermodel6.1 what would happen in a test case like use-native-low-precision.ll? Would we just expect to not see !0 = !{i32 1, !"dx.nativelowprec", i32 1}?

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The frontend is what is adding !0 = !{i32 1, !"dx.nativelowprec", i32 1}, so we wouldn't see it in the module.

If it is manually added to a module that is SM 6.1 or older, then it should have no effect on the shader flags.
Should I add a test for this?

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My concern was if the validator would allow the dxil if it was less than sm 6.2 and we saw nativelowprec set. The backend would be our last place to catch that and avoid the validator complaining.

If that isn't a concern then I don't think we need a test.

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@Icohedron Icohedron Apr 8, 2025 •
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I don't think the validator interprets any module metadata flag named "dx.nativelowpres", so it would just be ignored if it is present in the DXIL even when the SM is lower than 6.2.

NativeLowPrec->getValue() != 0)
SCCSF.UseNativeLowPrecision = true;

ComputedShaderFlags CSF;
for (const auto &BB : *F)
for (const auto &I : BB)
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45 changes: 45 additions & 0 deletions llvm/test/CodeGen/DirectX/ShaderFlags/use-native-low-precision.ll
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@@ -0,0 +1,45 @@
; RUN: opt -S --passes="print-dx-shader-flags" 2>&1 %s | FileCheck %s
; RUN: llc %s --filetype=obj -o - | obj2yaml | FileCheck %s --check-prefix=DXC

target triple = "dxil-pc-shadermodel6.7-library"

;CHECK: ; Combined Shader Flags for Module
;CHECK-NEXT: ; Shader Flags Value: 0x00800020
;CHECK-NEXT: ;
;CHECK-NEXT: ; Note: shader requires additional functionality:
;CHECK-NEXT: ; Note: extra DXIL module flags:
;CHECK-NEXT: ; D3D11_1_SB_GLOBAL_FLAG_ENABLE_MINIMUM_PRECISION
;CHECK-NEXT: ; Native 16bit types enabled
;CHECK-NEXT: ;
;CHECK-NEXT: ; Shader Flags for Module Functions

;CHECK-LABEL: ; Function add_i16 : 0x00800020
define i16 @add_i16(i16 %a, i16 %b) #0 {
%sum = add i16 %a, %b
ret i16 %sum
}

; NOTE: The flag for native low precision is set for every function in the
; module regardless of whether or not the function uses low precision data
; types. This matches the behavior in DXC
;CHECK-LABEL: ; Function add_i32 : 0x00800000
define i32 @add_i32(i32 %a, i32 %b) #0 {
%sum = add i32 %a, %b
ret i32 %sum
}

;CHECK-LABEL: ; Function add_half : 0x00800020
define half @add_half(half %a, half %b) #0 {
%sum = fadd half %a, %b
ret half %sum
}

attributes #0 = { convergent norecurse nounwind "hlsl.export" }

!llvm.module.flags = !{!0}
!0 = !{i32 1, !"dx.nativelowprec", i32 1}

; DXC: - Name: SFI0
; DXC-NEXT: Size: 8
; DXC-NOT: Flags:
; DXC: ...