[SPIRV] Allow __spirv_SpecConstant in Vulkan shaders

[s-perron]

There is a builtin __spirv_SpecConstant that the SPIR-V backend expands
into a specialization constant. However, it is currently only enable for
OpenCL shaders, and not the graphic shaders.

We want to use it for specialization constants coming from HLSL, so we
are enabling it for graphic shaders as well.

Implements llvm/wg-hlsl#287

Fixes #142991

[llvmbot]

@llvm/pr-subscribers-backend-spir-v

Author: Steven Perron (s-perron)

Changes

There is a builtin __spirv_SpecConstant that the SPIR-V backend expands
into a specialization constant. However, it is currently only enable for
OpenCL shaders, and not the graphic shaders.

We want to use it for specialization constants coming from HLSL, so we
are enabling it for graphic shaders as well.

---

Full diff: https://github.com/llvm/llvm-project/pull/143543.diff

2 Files Affected:

• (modified) llvm/lib/Target/SPIRV/SPIRVBuiltins.td (+2)
• (added) llvm/test/CodeGen/SPIRV/constant/spec-constant.ll (+90)

diff --git a/llvm/lib/Target/SPIRV/SPIRVBuiltins.td b/llvm/lib/Target/SPIRV/SPIRVBuiltins.td
index 6842e5ff067cf..401a762cd62a3 100644
--- a/llvm/lib/Target/SPIRV/SPIRVBuiltins.td
+++ b/llvm/lib/Target/SPIRV/SPIRVBuiltins.td
@@ -674,6 +674,8 @@ defm : DemangledNativeBuiltin<"ndrange_3D", OpenCL_std, Enqueue, 1, 3, OpBuildND
 
 // Spec constant builtin records:
 defm : DemangledNativeBuiltin<"__spirv_SpecConstant", OpenCL_std, SpecConstant, 2, 2, OpSpecConstant>;
+defm : DemangledNativeBuiltin<"__spirv_SpecConstant", GLSL_std_450,
+                              SpecConstant, 2, 2, OpSpecConstant>;
 defm : DemangledNativeBuiltin<"__spirv_SpecConstantComposite", OpenCL_std, SpecConstant, 1, 0, OpSpecConstantComposite>;
 
 // Async Copy and Prefetch builtin records:
diff --git a/llvm/test/CodeGen/SPIRV/constant/spec-constant.ll b/llvm/test/CodeGen/SPIRV/constant/spec-constant.ll
new file mode 100644
index 0000000000000..030eb1264ed66
--- /dev/null
+++ b/llvm/test/CodeGen/SPIRV/constant/spec-constant.ll
@@ -0,0 +1,90 @@
+; RUN: llc -verify-machineinstrs -O0 -mtriple=spirv1.6-unknown-vulkan1.3-compute %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv1.6-unknown-vulkan1.3-compute %s -o - -filetype=obj | spirv-val %}
+
+; CHECK-DAG: OpDecorate [[bool_const:%[0-9]+]] SpecId 1
+; CHECK-DAG: OpDecorate [[short_const:%[0-9]+]] SpecId 2
+; CHECK-DAG: OpDecorate [[int_const:%[0-9]+]] SpecId 3
+; CHECK-DAG: OpDecorate [[long_const:%[0-9]+]] SpecId 4
+; CHECK-DAG: OpDecorate [[float_const:%[0-9]+]] SpecId 8
+; CHECK-DAG: OpDecorate [[double_const:%[0-9]+]] SpecId 9
+; CHECK-DAG: OpDecorate [[enum_const:%[0-9]+]] SpecId 10
+
+; CHECK-DAG: [[bool_const]] = OpSpecConstantTrue {{%[0-9]+}}
+; CHECK-DAG: [[short_const]] = OpSpecConstant {{%[0-9]+}} 4
+; CHECK-DAG: [[int_const]] = OpSpecConstant {{%[0-9]+}} 5
+; CHECK-DAG: [[long_const]] = OpSpecConstant {{%[0-9]+}} 8
+; CHECK-DAG: [[float_const]] = OpSpecConstant {{%[0-9]+}} 1112014848
+; CHECK-DAG: [[double_const]] = OpSpecConstant {{%[0-9]+}} 0 1079574528
+; CHECK-DAG: [[enum_const]] = OpSpecConstant {{%[0-9]+}} 30
+
+@_ZL10bool_const = internal addrspace(10) global i32 0, align 4
+@_ZL11short_const = internal addrspace(10) global i16 0, align 2
+@_ZL9int_const = internal addrspace(10) global i32 0, align 4
+@_ZL10long_const = internal addrspace(10) global i64 0, align 8
+@_ZL11float_const = internal addrspace(10) global float 0.000000e+00, align 4
+@_ZL12double_const = internal addrspace(10) global double 0.000000e+00, align 8
+@_ZL10enum_const = internal addrspace(10) global i32 0, align 4
+
+; Function Attrs: mustprogress nofree noinline norecurse nosync nounwind willreturn memory(readwrite, argmem: none, inaccessiblemem: none)
+define void @main() local_unnamed_addr #0 {
+entry:
+  %0 = tail call spir_func i1 @_Z20__spirv_SpecConstantib(i32 1, i1 true)
+  %storedv.i.i = zext i1 %0 to i32
+  store i32 %storedv.i.i, ptr addrspace(10) @_ZL10bool_const, align 4, !tbaa !3
+  %1 = tail call ptr @llvm.invariant.start.p10(i64 4, ptr addrspace(10) @_ZL10bool_const)
+  %2 = tail call spir_func i16 @_Z20__spirv_SpecConstantis(i32 2, i16 4)
+  store i16 %2, ptr addrspace(10) @_ZL11short_const, align 2, !tbaa !7
+  %3 = tail call ptr @llvm.invariant.start.p10(i64 2, ptr addrspace(10) @_ZL11short_const)
+  %4 = tail call spir_func i32 @_Z20__spirv_SpecConstantii(i32 3, i32 5)
+  store i32 %4, ptr addrspace(10) @_ZL9int_const, align 4, !tbaa !9
+  %5 = tail call ptr @llvm.invariant.start.p10(i64 4, ptr addrspace(10) @_ZL9int_const)
+  %6 = tail call spir_func i64 @_Z20__spirv_SpecConstantix(i32 4, i64 8)
+  store i64 %6, ptr addrspace(10) @_ZL10long_const, align 8, !tbaa !11
+  %7 = tail call ptr @llvm.invariant.start.p10(i64 8, ptr addrspace(10) @_ZL10long_const)
+  %14 = tail call reassoc nnan ninf nsz arcp afn spir_func float @_Z20__spirv_SpecConstantif(i32 8, float 5.000000e+01)
+  store float %14, ptr addrspace(10) @_ZL11float_const, align 4, !tbaa !13
+  %15 = tail call ptr @llvm.invariant.start.p10(i64 4, ptr addrspace(10) @_ZL11float_const)
+  %16 = tail call reassoc nnan ninf nsz arcp afn spir_func double @_Z20__spirv_SpecConstantid(i32 9, double 1.000000e+02)
+  store double %16, ptr addrspace(10) @_ZL12double_const, align 8, !tbaa !15
+  %17 = tail call ptr @llvm.invariant.start.p10(i64 8, ptr addrspace(10) @_ZL12double_const)
+  %18 = tail call spir_func i32 @_Z20__spirv_SpecConstantii(i32 10, i32 30)
+  store i32 %18, ptr addrspace(10) @_ZL10enum_const, align 4, !tbaa !17
+  %19 = tail call ptr @llvm.invariant.start.p10(i64 4, ptr addrspace(10) @_ZL10enum_const)
+  ret void
+}
+
+
+declare i1 @_Z20__spirv_SpecConstantib(i32, i1)
+declare i8 @_Z20__spirv_SpecConstantia(i32, i8)
+declare i16 @_Z20__spirv_SpecConstantis(i32, i16)
+declare i32 @_Z20__spirv_SpecConstantii(i32, i32)
+declare i64 @_Z20__spirv_SpecConstantix(i32, i64)
+declare float @_Z20__spirv_SpecConstantif(i32, float)
+declare double @_Z20__spirv_SpecConstantid(i32, double)
+
+attributes #0 = { mustprogress nofree noinline norecurse nosync nounwind willreturn memory(readwrite, argmem: none, inaccessiblemem: none) "approx-func-fp-math"="true" "frame-pointer"="all" "hlsl.numthreads"="1,1,1" "hlsl.shader"="compute" "no-infs-fp-math"="true" "no-nans-fp-math"="true" "no-signed-zeros-fp-math"="true" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+attributes #1 = { mustprogress nocallback nofree nosync nounwind willreturn memory(none) }
+attributes #2 = { mustprogress nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+
+!llvm.module.flags = !{!0, !1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"frame-pointer", i32 2}
+!2 = !{!"clang version 21.0.0git ([email protected]:s-perron/llvm-project.git 060dd85ac525db3606a5ec7ca12ba346a7f075af)"}
+!3 = !{!4, !4, i64 0}
+!4 = !{!"bool", !5, i64 0}
+!5 = !{!"omnipotent char", !6, i64 0}
+!6 = !{!"Simple C++ TBAA"}
+!7 = !{!8, !8, i64 0}
+!8 = !{!"short", !5, i64 0}
+!9 = !{!10, !10, i64 0}
+!10 = !{!"int", !5, i64 0}
+!11 = !{!12, !12, i64 0}
+!12 = !{!"long long", !5, i64 0}
+!13 = !{!14, !14, i64 0}
+!14 = !{!"float", !5, i64 0}
+!15 = !{!16, !16, i64 0}
+!16 = !{!"double", !5, i64 0}
+!17 = !{!18, !18, i64 0}
+!18 = !{!"_ZTS1E", !5, i64 0}