[HLSL] Add descriptor table metadata parsing #142492

joaosaffran · 2025-06-02T22:03:04Z

Implements descriptor table parsing from root signature metadata. This is required to support root signatures in hlsl.
Closes: #126640

llvm/test/CodeGen/DirectX/root-signature-error-accumulation.ll

llvm/lib/Target/DirectX/DXILRootSignature.cpp

inbelic · 2025-06-17T22:33:08Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+    return Flags == FlagT::DESCRIPTORS_VOLATILE;
+  }
+
+  // The data-specific flags are mutually exclusive.


the descriptor flags are also mutually exclusive. Do we want an explicit check for this? It seems like it is covered below. Maybe it is good for clarity?

bogner · 2025-06-18T20:04:22Z

llvm/include/llvm/BinaryFormat/DXContainerConstants.def

+DESCRIPTOR_RANGE(1, UAV)
+DESCRIPTOR_RANGE(2, CBV)
+DESCRIPTOR_RANGE(3, Sampler)
+DESCRIPTOR_RANGE(4, NONE)


Why do we have a value for NONE here? A value of 4 in the metadata would certainly be invalid, and this appears to be unused.

This came as a request from another PR, where Finn mentioned those values are useful in the frontend, since we are planning on sharing this, I've added those back.

Do you have a link to that conversation handy? I'd like to see how NONE would be used here...

Here is an example use case of NONE in the frontend:

llvm-project/clang/lib/Parse/ParseHLSLRootSignature.cpp

Line 87 in 5f69d68

std::optional<RootFlags> Flags = RootFlags::None;

.

But that discussion was in the context of flags, I will remove this one from here, since it doesn't seem to match the pattern of other NONE values

bogner · 2025-06-18T20:09:03Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+          .Default(-1u);
+
+  if (Range.RangeType == -1u)


Clearer to use ~0U rather than -1U, and this way avoids some warnings from MSVC in any case.

bogner · 2025-06-18T20:12:47Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

@@ -174,6 +174,94 @@ static bool parseRootDescriptors(LLVMContext *Ctx,
  return false;
 }

+static bool parseDescriptorRange(LLVMContext *Ctx,
+                                 mcdxbc::RootSignatureDesc &RSD,


Why is RSD passed in here?

bogner · 2025-06-18T20:18:13Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+  if (Version == 1) {
+    if (IsSampler)
+      return Flags == FlagT::NONE;
+    return Flags == FlagT::DESCRIPTORS_VOLATILE;
+  }


These values are still incorrect. As I mentioned in #142492 (comment) samplers can only have DESCRIPTORS_VOLATILE, and otherwise this needs to be DATA_VOLATILE.

Also, please add a test for this - we should be catching that this is obviously wrong.

There is some confusion in the spec, there are 2 sections saying different values are valid for this field. Reached in private to discuss this.

I'll add the test.

bogner · 2025-06-18T20:22:48Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+  // When no descriptor flag is set, any data flag is allowed.
+  return (Flags & ~DataFlags) == FlagT::NONE;


This is not correct. Samplers can never have the DATA_* flags set.

bogner · 2025-06-18T20:28:57Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+          OS << indent(2) << "- Range Type: " << Range.RangeType << "\n";
+          OS << indent(4) << "Register Space: " << Range.RegisterSpace << "\n";
+          OS << indent(4)
+             << "Base Shader Register: " << Range.BaseShaderRegister << "\n";
+          OS << indent(4) << "Num Descriptors: " << Range.NumDescriptors
+             << "\n";
+          OS << indent(4) << "Offset In Descriptors From Table Start: "
+             << Range.OffsetInDescriptorsFromTableStart << "\n";
+          if (RS.Version > 1)
+            OS << indent(4) << "Flags: " << Range.Flags << "\n";


Maybe it's just me, but I find using the indent() function with a small constant to be quite a bit less clear than just putting the spaces in the strings. Consider:

OS << " - Range Type: " << Range.RangeType << "\n" << " Register Space: " << Range.RegisterSpace << "\n" << " Base Shader Register: " << Range.BaseShaderRegister << "\n" << " Num Descriptors: " << Range.NumDescriptors << "\n" << " Offset In Descriptors From Table Start: " << Range.OffsetInDescriptorsFromTableStart << "\n"; if (RS.Version > 1) OS << " Flags: " << Range.Flags << "\n";

Here, you can see how the strings line up just by looking at them. Though admittedly it can get a bit messier with longer lines. IMO indent() is mostly useful when the indentation varies depending on context, or is large enough that just writing it out makes things less readable.

…or-table

bogner

LGTM other than a couple of fairly minor comments inline.

bogner · 2025-06-18T23:15:19Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+  const bool IsSampler =
+      (Type == llvm::to_underlying(dxbc::DescriptorRangeType::Sampler));
+
+  if (Version == 1) {


Probably worth a comment.

Suggested change

if (Version == 1) {

if (Version == 1) {

// Since the metadata is unversioned, we expect to explicitly see the values

// that map to the version 1 behaviour here.

bogner · 2025-06-20T03:51:19Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+  // When no descriptor flag is set, any data flag is allowed.
+  if (!IsSampler)
+    return (Flags & ~DataFlags) == FlagT::NONE;
+  return (Flags & ~FlagT::NONE) == FlagT::NONE;


It feels weird to do this case differently than above, since they're doing the same thing. Technically we could simplify this just by removing the DESCRIPTORS_STATIC_KEEPING_BUFFER_BOUNDS_CHECKS if condition, since that logic should be correct whether or not that flag is set, but I can see why you might avoid that so that the comments and the code flow are clear. In that case, I guess we should repeat the explicit approach as we did in the two other cases above:

Suggested change

// When no descriptor flag is set, any data flag is allowed.

if (!IsSampler)

return (Flags & ~DataFlags) == FlagT::NONE;

return (Flags & ~FlagT::NONE) == FlagT::NONE;

// When no descriptor flag is set, any data flag is allowed.

FlagT Mask = FlagT::None;

if (!IsSampler) {

Mask |= FlagT::DATA_VOLATILE;

Mask |= FlagT::DATA_STATIC;

Mask |= FlagT::DATA_STATIC_WHILE_SET_AT_EXECUTE;

}

return (Flags & ~Mask) == FlagT::NONE;

bogner · 2025-06-20T03:51:56Z

llvm/lib/Target/DirectX/DXILRootSignature.cpp

+
+        if (!verifyDescriptorRangeFlag(RSD.Version, Range.RangeType,
+                                       Range.Flags))
+          return reportValueError(Ctx, "DescriptorFlag", Range.Flags);


Should this differentiate from non-range DescriptorFlag?

Suggested change

return reportValueError(Ctx, "DescriptorFlag", Range.Flags);

return reportValueError(Ctx, "DescriptorRangeFlag", Range.Flags);

bogner · 2025-06-21T00:12:25Z

llvm/test/CodeGen/DirectX/ContainerData/RootSignature-DescriptorTable.ll

+; DXC-NEXT:                NumDescriptors:  0
+; DXC-NEXT:                BaseShaderRegister: 1
+; DXC-NEXT:                RegisterSpace:   0
+; DXC-NEXT:                OffsetInDescriptorsFromTableStart: 4294967295


Shouldn't this be 0?

OffsetInDescriptorsFromTableStart, is the 5th value in the metadata representation, in the first range this value is -1, which denote the special case where it was set to D3D12_DESCRIPTOR_RANGE_OFFSET_APPEND, here is a link to the docs describing this: OffsetInDescriptorsFromTableStart

Implements descriptor table parsing from root signature metadata. This is required to support root signatures in hlsl. Closes: #[126640](llvm#126640) --------- Co-authored-by: joaosaffran <[email protected]>

joaosaffran added 30 commits April 24, 2025 22:06

adding support for Root Descriptors

0abacfc

clean up

8b8c02a

addressing comments

7ac9641

formating

c105458

try fix test

efe76aa

addressing comments

a928e9d

refactoring mcdxbc struct to store root parameters out of order

a38f10b

changing name

9a7c359

changing variant to host pointers

d6c2b55

clean up

93e4cf2

fix

b45b1b6

fix

f804a23

fix naming

15eb6f5

fix naming

b9d7f07

addressing comments

46cc8c1

addressing comments

1b3e10a

addressing comments

1f31957

clean up

e8fbfce

removing v parameter

a31e5a5

Merge branch 'obj2yaml/root-descriptors' into refactoring/remove-union

a394ad0

clean up

ad415a7

Merge branch 'main' into refactoring/remove-union

8ff4845

adding support for root descriptors

f875555

removing none as a flag option

4f7f998

adding tests

3eb5e10

clean up and add more tests

58e1789

addressing comments

81915ad

Merge branch 'main' into metadata/root-descriptors

a515e28

clean

0d54162

cleanup

7f70dc5

joaosaffran requested review from bogner, inbelic and alsepkow and removed request for nikic and a team June 17, 2025 18:19

inbelic reviewed Jun 17, 2025

View reviewed changes

joaosaffran added 3 commits June 18, 2025 18:31

remove empty file

638d961

adding check for mutually exclusive descriptor flags

8b831f8

format

5c677a5

bogner reviewed Jun 18, 2025

View reviewed changes

joaosaffran added 5 commits June 18, 2025 22:15

address comments

bce790c

remove value

fefe820

adding support to version in metadata

e577503

fix tests

746c54a

Merge branch 'metadata/add-versioning-support' into metadata/descript…

c5a1009

…or-table

joaosaffran changed the base branch from main to users/joaosaffran/144957 June 19, 2025 21:28

add test

a66e6a3

joaosaffran mentioned this pull request Jun 20, 2025

[DirectX] Improve error handling and validation in root signature parsing #144577

Closed

joaosaffran changed the base branch from users/joaosaffran/144957 to main June 20, 2025 00:41

joaosaffran added 2 commits June 20, 2025 00:42

Merge branch 'main' into metadata/descriptor-table

351eee2

fix merge and test issues

4a0a955

joaosaffran requested review from bogner and inbelic June 20, 2025 01:46

bogner approved these changes Jun 20, 2025

View reviewed changes

addressing comments

4e655da

joaosaffran merged commit b5d5708 into llvm:main Jun 20, 2025
8 checks passed

bogner reviewed Jun 21, 2025

View reviewed changes

		// When no descriptor flag is set, any data flag is allowed.
		return (Flags & ~DataFlags) == FlagT::NONE;

-  // When no descriptor flag is set, any data flag is allowed.
-  if (!IsSampler)
-    return (Flags & ~DataFlags) == FlagT::NONE;
-  return (Flags & ~FlagT::NONE) == FlagT::NONE;
+  // When no descriptor flag is set, any data flag is allowed.
+  FlagT Mask = FlagT::None;
+  if (!IsSampler) {
+    Mask |= FlagT::DATA_VOLATILE;
+    Mask |= FlagT::DATA_STATIC;
+    Mask |= FlagT::DATA_STATIC_WHILE_SET_AT_EXECUTE;
+  }
+  return (Flags & ~Mask) == FlagT::NONE;

	return reportValueError(Ctx, "DescriptorFlag", Range.Flags);
	return reportValueError(Ctx, "DescriptorRangeFlag", Range.Flags);

[HLSL] Add descriptor table metadata parsing #142492

[HLSL] Add descriptor table metadata parsing #142492

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joaosaffran commented Jun 2, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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joaosaffran Jun 18, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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joaosaffran commented Jun 2, 2025 •

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