简介 本文主要关注 SPIR-V 1.6。
前面分支 / 循环 / 函数等测试主要是在 Fragment 这种 OpEntrypoint 下调用的子函数内部进行测试的。
下面的实验基本使用 Shader Playground 的 glslang trunk (上面写使用的 2022-09-19 的版本)，其中：
Shader stage 选择 frag
Target 选择 Vulkan 1.3
Output format 选择 SPIR-V
See Also
例子
通过例子来学习 SPIR-V 会比较快捷，也比较容易理解。
SPIR-V 本身是 SSA 形式的 IR，且指令 format 较为规整，易于解析 (虽然大家都是调库，也不会用手解析 SPIR-V 的)。
规范文档参考：
同时推荐用 Shader Playground 来方便直接看到 SPIR-V Disassembly。
据博主本人测试，OpenAI 的 GPT-4 有不错 的 SPIR-V 到 GLSL 反汇编能力。
Layout 从反汇编结果可以看到，SPIR-V Module 有比较整齐的形式，事实上这些形式是规定好的：Logical Layout of a Module - SPIR-V Specification 。
概观 1 2 3 4 5 6 #version 310 es precision highp float ; precision highp int ; precision mediump sampler3D; void main () {}
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 ; SPIR-V ; Version: 1.6 ; Generator: Khronos Glslang Reference Front End; 10 ; Bound: 6 ; Bound; where all <id>s in this module are ; guaranteed to satisfy 0 < id < Bound ; Schema: 0 ; Instruction Schema; Reserved, not used for now OpCapability Shader %1 = OpExtInstImport "GLSL.std.450" OpMemoryModel Logical GLSL450 ; Addressing model = Logical ; Logical 模式下面，指针只能从已有的对象中创建，指针的地址也都是假的 ; （也就是说，不能把指针的值拷贝到别的变量中去） ; 也有一些带有物理指针的 Addressing Model 和相应的 Memory Model ; => 留待后文探索 ; Memory Model = GLSL450 OpEntryPoint Fragment %main "main" ; Execution Model = Fragment ; Entrypoint = %main (用 OpFunction 定义的某个 Result ID) ; Name = "main" (Entrypoint 要有一个字符串名字) OpExecutionMode %main OriginUpperLeft ; The coordinates decorated by FragCoord ; appear to originate in the upper left, ; and increase toward the right and downward. ; Only valid with the Fragment Execution Model. OpSource ESSL 310 ; 标记源语言; ESSL = OpenGL ES Shader Language OpName %main "main" %void = OpTypeVoid %3 = OpTypeFunction %void %main = OpFunction %void None %3 %5 = OpLabel OpReturn OpFunctionEnd
这里会发现 %main 这个 result id 是在后面定义的，但是前面却引用到了。
对于 SPV_OPERAND_TYPE_ID, SPV_OPERAND_TYPE_MEMORY_SEMANTICS_ID, SPV_OPERAND_TYPE_SCOPE_ID 来说，正常都需要先定义（是某个指令的 result id）再引用，但是可以前向定义的指令除外。
可前向定义的指令可以参考 source/val/validate_id.cpp:L122 @ SPIRV-Tools ，其中包括：
全部的 OpTypeXXX 类指令
其它一大堆，主要是执行模式等 metadata、Decorate、分支、device side invoke 等
可以参考 spvOperandCanBeForwardDeclaredFunction (source/operand.cpp @ SPIRV-Tools) 这个函数
简单的函数 函数定义：
1 2 3 4 5 6 7 8 9 10 11 12 #version 310 es float Circle ( vec2 uv, vec2 p, float r, float blur ) { float d = length(uv - p); float c = smoothstep(r, r-blur, d); return c; }
SPIR-V 反汇编：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 ; == 相关定义 == %1 = OpExtInstImport "GLSL.std.450" ; 引入外部指令集 %float = OpTypeFloat 32 %v2float = OpTypeVector %float 2 %_ptr_Function_v2float = OpTypePointer Function %v2float %_ptr_Function_float = OpTypePointer Function %float ; 定义指针类型，指向的变量的 Storage Class 为 Function %10 = OpTypeFunction %float %_ptr_Function_v2float %_ptr_Function_v2float %_ptr_Function_float %_ptr_Function_float ; == 函数 == %Circle_vf2_vf2_f1_f1_ = OpFunction %float None %10 ; 返回值类型 %float，Function Control 类型无 ; 函数类型 %10 - float (vec2, vec2, float, float) %uv = OpFunctionParameter %_ptr_Function_v2float ; 拿到各个 parameter 的 result id %p = OpFunctionParameter %_ptr_Function_v2float %r = OpFunctionParameter %_ptr_Function_float %blur = OpFunctionParameter %_ptr_Function_float %16 = OpLabel ; 一个基本块的开始 (2.2.5. Control Flow) %d = OpVariable %_ptr_Function_float Function ; 定义 float 变量, Storage Class 为 Function %c = OpVariable %_ptr_Function_float Function ; => 变量可以被 OpLoad / OpStore %39 = OpLoad %v2float %uv ; 结果类型 %v2float, 装载 %uv 变量的值 %40 = OpLoad %v2float %p %41 = OpFSub %v2float %39 %40 ; Operand2 - Operand1，结果类型 %v2float %42 = OpExtInst %float %1 Length %41 ; Execute an instruction in an imported set of extended instructions ; Set (也就是这里的 %1) is the result of an OpExtInstImport instruction. ; 后面的 Set 中的 Instruction 是 “Length”，操作数是 %41 OpStore %d %42 ; 存到 %d 变量的存储中 %44 = OpLoad %float %r %45 = OpLoad %float %r %46 = OpLoad %float %blur %47 = OpFSub %float %45 %46 ; %blur - %r %48 = OpLoad %float %d %49 = OpExtInst %float %1 SmoothStep %44 %47 %48 ; SmoothStep(%r, %blur - %r, %d) OpStore %c %49 %50 = OpLoad %float %c OpReturnValue %50 ; 不返回值的话使用 OpReturn OpFunctionEnd
函数的 in / out 参数 函数定义：
1 2 3 4 void inoutTest (in vec2 uv, out float o1, in float i2, out vec2 o2) { o2 = uv; o1 = i2; }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 %main = OpFunction %void None %3 %5 = OpLabel %v1 = OpVariable %_ptr_Function_v2float Function %t1 = OpVariable %_ptr_Function_float Function %t2 = OpVariable %_ptr_Function_float Function %v2 = OpVariable %_ptr_Function_v2float Function %param = OpVariable %_ptr_Function_v2float Function %param_0 = OpVariable %_ptr_Function_float Function %param_1 = OpVariable %_ptr_Function_float Function %param_2 = OpVariable %_ptr_Function_v2float Function %24 = OpLoad %v2float %v1 OpStore %param %24 %27 = OpLoad %float %t2 OpStore %param_1 %27 %29 = OpFunctionCall %void %inoutTest_vf2_f1_f1_vf2_ %param %param_0 %param_1 %param_2 %30 = OpLoad %float %param_0 ; 可以看到，就是实现了 %param_0 变量内值的变化 OpStore %t1 %30 %31 = OpLoad %v2float %param_2 OpStore %v2 %31 OpStore %fragColor %38 OpReturn OpFunctionEnd %inoutTest_vf2_f1_f1_vf2_ = OpFunction %void None %10 %uv = OpFunctionParameter %_ptr_Function_v2float %o1 = OpFunctionParameter %_ptr_Function_float %i2 = OpFunctionParameter %_ptr_Function_float %o2 = OpFunctionParameter %_ptr_Function_v2float %16 = OpLabel %17 = OpLoad %v2float %uv OpStore %o2 %17 %18 = OpLoad %float %i2 OpStore %o1 %18 OpReturn OpFunctionEnd
分支 1 2 3 4 5 6 7 8 9 10 11 12 #version 310 es int testIf (float range) { int c = 0 ; if (range < 1.0 ) c = 1 ; else c = 2 ; return c; }
SPIR-V 反汇编：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 ; == 相关定义 == %int_0 = OpConstant %int 0 %float_1 = OpConstant %float 1 ; == 函数 == %testIf_f1_ = OpFunction %int None %22 %range = OpFunctionParameter %_ptr_Function_float %25 = OpLabel ; 基本块开始 %c_0 = OpVariable %_ptr_Function_int Function OpStore %c_0 %int_0 %68 = OpLoad %float %range %71 = OpFOrdLessThan %bool %68 %float_1 ; check if %68 (loaded from %range) < %float_1 OpSelectionMerge %73 None ; Declare a structured selection ; This instruction must immediately precede either an OpBranchConditional or OpSwitch instruction. That is, it must be the second-to-last instruction in its block. ; Selection Control = None; 这里可以给 Hint 提示此分支是否应该 remove ; 并且指定 Merge Block 为 %73，也就是分支结束的地方 OpBranchConditional %71 %72 %75 ; 如果 %71 为 true, 则跳到 %72 标号，否则跳到 %75 标号 - 标志基本块结束 %72 = OpLabel ; OpStore %c_0 %int_1 OpBranch %73 ; Unconditional branch to %73 %75 = OpLabel OpStore %c_0 %int_2 OpBranch %73 %73 = OpLabel %77 = OpLoad %int %c_0 OpReturnValue %77 OpFunctionEnd
总结：
OpSelectionMergeOpBranchConditional两个基本块最后 OpBranch 到出口
循环 术语
Merge Instruction: OpSelectionMerge 或者 OpLoopMerge 两者之一，用在
Header Block: 包含 Merge Instruction 的 Block
Loop Header: Merge Instruction 是 OpLoopMerge 的 Header Block
Selection Header: OpSelectionMerge 为 Merge Instruction, OpBranchConditional 是终止指令的 Header Block
Switch Header: OpSelectionMerge 为 Merge Instruction, OpSwitch 是终止指令的 Header Block
Merge Block: 在 Merge Instruction 作为 Merge Block 操作数的 Block
Break Block: 含有跳转到被 Loop Header 的 Merge Instruction 定义为 Merge Block 的 Block
Continue Block: 含有跳转到 OpLoopMerge 指令的 Continue Target 的 Block
Return Block: 包含 OpReturn 或者 OpReturnValue 的 Block
GPT-4: 在 SPIR-V 中，Merge Block 是一个特定类型的基本块（Basic Block），用于控制流程结构中收敛控制流的位置。当你在 SPIR-V 中使用分支结构（如 if-else 语句、循环等）时，Merge Block 表示在这些分支结构末端的汇合点。
SPIR-V 中的控制流结构使用特殊的操作码（如 OpSelectionMerge、OpLoopMerge）来定义。这些操作码告诉编译器如何解释控制流图（Control Flow Graph，CFG）。Merge Block 用于表示这些控制流结构的结束位置，它是控制流从不同路径重新合并到一条路径的地方。例如，一个 if-else 语句会有两个分支，这两个分支在 Merge Block 之后合并为单个执行路径。
while 循环 - 无 break 1 2 3 4 5 6 7 8 int testWhile (int count) { int sum = 0 ; while (count >= 0 ) { sum++; count--; } return sum; }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 %testWhile_i1_ = OpFunction %int None %27 %count = OpFunctionParameter %_ptr_Function_int %30 = OpLabel %sum = OpVariable %_ptr_Function_int Function OpStore %sum %int_0 OpBranch %85 %85 = OpLabel OpLoopMerge %87 %88 None ; Declare a structured loop. ; This instruction must immediately precede ; either an OpBranch or OpBranchConditional ; instruction. ; That is, it must be the second-to-last ; instruction in its block. ; Merge Block = %87 ; Continue target = %88 OpBranch %89 %89 = OpLabel %90 = OpLoad %int %count %91 = OpSGreaterThanEqual %bool %90 %int_0 ; 有符号比较; if %90 (=count) >= %int_0 (0) OpBranchConditional %91 %86 %87 ; %91 == true ? jump to %86 : jump to %87 (FINISH) %86 = OpLabel %92 = OpLoad %int %sum %93 = OpIAdd %int %92 %int_1 OpStore %sum %93 ; sum = sum + 1 %94 = OpLoad %int %count %95 = OpISub %int %94 %int_1 OpStore %count %95 ; count = count - 1 OpBranch %88 %88 = OpLabel OpBranch %85 ; 无条件回到 Loop 头 %87 = OpLabel %96 = OpLoad %int %sum OpReturnValue %96 OpFunctionEnd
相当于翻译成了如下格式的 SPIR-V：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 %header_block = OpLabel OpLoopMerge %merge_block %continue_block OpBranch %loop_body %loop_test = OpLabel OpLoopMerge %loop_merge %loop_cont %loop_cond = ... ; Some calculations OpBranchConditional %loop_cond %loop_body %loop_merge %loop_body = OpLabel ... ; Some codes inside loop body OpBranch %loop_cont %loop_cont = OpLabel OpBranch %loop_test %loop_merge = OpLabel ... ; The "following" basic block
while 循环 - 带 break 1 2 3 4 5 6 7 8 9 10 11 int testWhile (int count) { int sum = 0 ; while (count >= 0 ) { sum++; count--; if (count == 2 ) { break ; } } return sum; }
SPIR-V 反汇编：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 %testWhile_i1_ = OpFunction %int None %27 %count = OpFunctionParameter %_ptr_Function_int %30 = OpLabel %sum = OpVariable %_ptr_Function_int Function OpStore %sum %int_0 OpBranch %85 %85 = OpLabel OpLoopMerge %87 %88 None OpBranch %89 %89 = OpLabel %90 = OpLoad %int %count %91 = OpSGreaterThanEqual %bool %90 %int_0 OpBranchConditional %91 %86 %87 %86 = OpLabel %92 = OpLoad %int %sum %93 = OpIAdd %int %92 %int_1 OpStore %sum %93 %94 = OpLoad %int %count %95 = OpISub %int %94 %int_1 OpStore %count %95 %96 = OpLoad %int %count %97 = OpIEqual %bool %96 %int_2 OpSelectionMerge %99 None ; If 的 Merge Block = %99 OpBranchConditional %97 %98 %99 %98 = OpLabel OpBranch %87 ; => break out of the loop => emit instruction ; to branch to while's merge block %99 = OpLabel ; 正常走 => 到达 while 末尾 => emit 到 while OpBranch %88 ; 的 Continue Block %88 = OpLabel ; Continue Block OpBranch %85 %87 = OpLabel ; Merge Block %101 = OpLoad %int %sum OpReturnValue %101 OpFunctionEnd
总结：
break 作为一个基本块末尾，直接 emit 无条件 branch 来跳到 while 循环的 merge block。
for 循环 GLSL 代码：
1 2 3 4 5 6 7 int testFor (int count) { int sum = 0 ; for (int i = 0 ; i < count; i++) { sum += 1 ; } return sum; }
SPIR-V 反汇编：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 %testFor_i1_ = OpFunction %int None %27 %count_0 = OpFunctionParameter %_ptr_Function_int %33 = OpLabel %sum_0 = OpVariable %_ptr_Function_int Function %i = OpVariable %_ptr_Function_int Function OpStore %sum_0 %int_0 OpStore %i %int_0 OpBranch %109 %109 = OpLabel OpLoopMerge %111 %112 None OpBranch %113 %113 = OpLabel %114 = OpLoad %int %i %115 = OpLoad %int %count_0 %116 = OpSLessThan %bool %114 %115 OpBranchConditional %116 %110 %111 %110 = OpLabel %117 = OpLoad %int %sum_0 %118 = OpIAdd %int %117 %int_1 OpStore %sum_0 %118 OpBranch %112 %112 = OpLabel ; Continuation Block %119 = OpLoad %int %i ; for 循环的循环结束操作放到了这里 %120 = OpIAdd %int %119 %int_1 OpStore %i %120 OpBranch %109 %111 = OpLabel ; Merge Block %121 = OpLoad %int %sum_0 OpReturnValue %121 OpFunctionEnd
总结：
Continuation Block 处现在 emit 了循环后维护操作
OpSource, OpName, OpMemberName 属于调试信息。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 #version 310 es precision highp float ; precision highp int ; precision mediump sampler3D; layout(binding = 0 ) uniform uniBlock { uniform vec3 lightPos; uniform float someOtherFloat; }; layout(location = 0 ) out vec4 outColor; layout(location = 0 ) in vec4 vertColor; void mainImage (out vec4 c, in vec2 f, in vec3 lightPos) {}void main () {mainImage(outColor, gl_FragCoord.xy, lightPos);}
所有可选 Decoration 可以参考 https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#Decoration
对于 gl_FragCoord：
1 2 3 4 OpName %gl_FragCoord "gl_FragCoord" OpDecorate %gl_FragCoord BuiltIn FragCoord %_ptr_Input_v4float = OpTypePointer Input %v4float %gl_FragCoord = OpVariable %_ptr_Input_v4float Input
对于 Input Variable：
1 2 3 4 OpName %vertColor "vertColor" OpDecorate %vertColor Location 0 %_ptr_Input_v4float = OpTypePointer Input %v4float %vertColor = OpVariable %_ptr_Input_v4float Input
对于 Output Variable：
1 2 3 4 OpName %outColor "outColor" OpDecorate %outColor Location 0 %_ptr_Output_v4float = OpTypePointer Output %v4float %outColor = OpVariable %_ptr_Output_v4float Output
使用时直接 OpLoad 就可以。
匿名的 Uniform Block，其成员是被引入了 Global Scope 的。
可以作为 OpenGL 的 uniforms outside a block 的平替。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 OpName %uniBlock "uniBlock" OpMemberName %uniBlock 0 "lightPos" OpMemberName %uniBlock 1 "someOtherFloat" OpName %_ "" OpMemberDecorate %uniBlock 0 Offset 0 ; Structure type = %uniBlock ; Member = 0 ; Decoration = Offset ; Byte Offset = 0 OpMemberDecorate %uniBlock 1 Offset 12 OpDecorate %uniBlock Block ; Apply only to a structure type to establish ; it is a memory interface block OpDecorate %_ DescriptorSet 0 ; Apply only to a variable. ; Descriptor Set is an unsigned 32-bit integer ; forming part of the linkage between the client ; API and SPIR-V memory buffers, images, etc. ; See the client API specification for more detail. OpDecorate %_ Binding 0 ; Apply only to a variable. ; Binding Point is an unsigned 32-bit integer ; forming part of the linkage between the client ; API and SPIR-V memory buffers, images, etc. ; See the client API specification for more detail. %uniBlock = OpTypeStruct %v3float %float ; 后面指定所有成员的类型，这里是 {vec3, float} %_ptr_Uniform_uniBlock = OpTypePointer Uniform %uniBlock ; Storage Class = Uniform %_ = OpVariable %_ptr_Uniform_uniBlock Uniform %_ptr_Uniform_v3float = OpTypePointer Uniform %v3float %34 = OpAccessChain %_ptr_Uniform_v3float %_ %int_0 ; Create a pointer into a composite object. ; Base = %_, Indexes = {%int_0} ; Each index in Indexes ; - must have a scalar integer type ; - is treated as signed ; - if indexing into a structure, must be an ; OpConstant whose value is in bounds for selecting a member ; - if indexing into a vector, array, or matrix, ; with the result type being a logical pointer type, ; causes undefined behavior if not in bounds. %35 = OpLoad %v3float %34
把上面的示例程序里面的 uniform uniBlock 类型的不具名 Uniform Block 加一个实例名字：
1 2 3 4 5 6 7 layout(binding=0 ) uniform uniBlock { uniform vec3 lightPos; uniform float someOtherFloat; } uniInst; void main () {mainImage(outColor, gl_FragCoord.xy, uniInst.lightPos);}
下面是相关的 SPIR-V：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 OpName %uniInst "uniInst" OpDecorate %gl_FragCoord BuiltIn FragCoord OpMemberDecorate %uniBlock 0 Offset 0 OpMemberDecorate %uniBlock 1 Offset 12 OpDecorate %uniBlock Block OpDecorate %uniInst DescriptorSet 0 OpDecorate %uniInst Binding 0 %uniBlock = OpTypeStruct %v3float %float %_ptr_Uniform_uniBlock = OpTypePointer Uniform %uniBlock %uniInst = OpVariable %_ptr_Uniform_uniBlock Uniform %_ptr_Uniform_uniBlock = OpTypePointer Uniform %uniBlock %uniInst = OpVariable %_ptr_Uniform_uniBlock Uniform %34 = OpAccessChain %_ptr_Uniform_v3float %uniInst %int_0 %35 = OpLoad %v3float %34
可以看到，主要区别是 %_ 变成了 %uniInst，其实就是 OpName 从 "" 变成了 "uniInst"，这样 SPIR-V 反汇编工具生成的反汇编能更好看一些而已。真正的 Result ID 等的逻辑关系都是没有变化的。
当然，不知道反射库依赖不依赖 OpName，当然去掉了也不是没法反射就是了，只要 layout 一样，怼上去就得了。
Sampler GLSL 源码：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 #version 450 layout (binding = 1 ) uniform sampler2D samplerColor; layout (binding = 2 ) uniform texture2D tex; layout (binding = 3 ) uniform sampler samp; layout (location = 0 ) in vec2 inUV; layout (location = 1 ) in float inLodBias; layout (location = 0 ) out vec4 outFragColor; void main () { vec4 color = texture(samplerColor, inUV, inLodBias); vec4 color2 = texture(sampler2D(tex, samp), inUV, inLodBias); outFragColor = color + color2; }
SPIR-V 反汇编：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 ; SPIR-V ; Version: 1.0 ; Generator: Khronos Glslang Reference Front End; 10 ; Bound: 40 ; Schema: 0 OpCapability Shader %1 = OpExtInstImport "GLSL.std.450" OpMemoryModel Logical GLSL450 OpEntryPoint Fragment %main "main" %inUV %inLodBias %outFragColor OpExecutionMode %main OriginUpperLeft OpSource GLSL 450 OpName %main "main" OpName %color "color" OpName %samplerColor "samplerColor" OpName %inUV "inUV" OpName %inLodBias "inLodBias" OpName %color2 "color2" OpName %tex "tex" OpName %samp "samp" OpName %outFragColor "outFragColor" OpDecorate %samplerColor DescriptorSet 0 OpDecorate %samplerColor Binding 1 OpDecorate %inUV Location 0 OpDecorate %inLodBias Location 1 OpDecorate %tex DescriptorSet 0 OpDecorate %tex Binding 2 OpDecorate %samp DescriptorSet 0 OpDecorate %samp Binding 3 OpDecorate %outFragColor Location 0 %void = OpTypeVoid %3 = OpTypeFunction %void %float = OpTypeFloat 32 %v4float = OpTypeVector %float 4 %_ptr_Function_v4float = OpTypePointer Function %v4float %10 = OpTypeImage %float 2D 0 0 0 1 Unknown %11 = OpTypeSampledImage %10 %_ptr_UniformConstant_11 = OpTypePointer UniformConstant %11 %samplerColor = OpVariable %_ptr_UniformConstant_11 UniformConstant %v2float = OpTypeVector %float 2 %_ptr_Input_v2float = OpTypePointer Input %v2float %inUV = OpVariable %_ptr_Input_v2float Input %_ptr_Input_float = OpTypePointer Input %float %inLodBias = OpVariable %_ptr_Input_float Input %_ptr_UniformConstant_10 = OpTypePointer UniformConstant %10 %tex = OpVariable %_ptr_UniformConstant_10 UniformConstant %27 = OpTypeSampler %_ptr_UniformConstant_27 = OpTypePointer UniformConstant %27 %samp = OpVariable %_ptr_UniformConstant_27 UniformConstant %_ptr_Output_v4float = OpTypePointer Output %v4float %outFragColor = OpVariable %_ptr_Output_v4float Output %main = OpFunction %void None %3 %5 = OpLabel %color = OpVariable %_ptr_Function_v4float Function %color2 = OpVariable %_ptr_Function_v4float Function %14 = OpLoad %11 %samplerColor %18 = OpLoad %v2float %inUV %21 = OpLoad %float %inLodBias %22 = OpImageSampleImplicitLod %v4float %14 %18 Bias %21 OpStore %color %22 %26 = OpLoad %10 %tex %30 = OpLoad %27 %samp %31 = OpSampledImage %11 %26 %30 %32 = OpLoad %v2float %inUV %33 = OpLoad %float %inLodBias %34 = OpImageSampleImplicitLod %v4float %31 %32 Bias %33 OpStore %color2 %34 %37 = OpLoad %v4float %color %38 = OpLoad %v4float %color2 %39 = OpFAdd %v4float %37 %38 OpStore %outFragColor %39 OpReturn OpFunctionEnd
总结如下：
Sampler (VK_DESCRIPTOR_TYPE_SAMPLER)1 2 3 4 5 6 7 OpName %samp "samp" OpDecorate %samp DescriptorSet 0 OpDecorate %samp Binding 3 %27 = OpTypeSampler %_ptr_UniformConstant_27 = OpTypePointer UniformConstant %27 %samp = OpVariable %_ptr_UniformConstant_27 UniformConstant
Sampled Image (VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE)1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 OpName %tex "tex" OpDecorate %tex DescriptorSet 0 OpDecorate %tex Binding 2 %10 = OpTypeImage %float 2D 0 0 0 1 Unknown %_ptr_UniformConstant_10 = OpTypePointer UniformConstant %10 %tex = OpVariable %_ptr_UniformConstant_10 UniformConstant ; 使用 %26 = OpLoad %10 %tex %30 = OpLoad %27 %samp %31 = OpSampledImage %11 %26 %30 %32 = OpLoad %v2float %inUV %33 = OpLoad %float %inLodBias %34 = OpImageSampleImplicitLod %v4float %31 %32 Bias %33
Combined Image Sampler (VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER)1 2 3 4 5 6 7 8 9 10 11 12 13 14 OpName %samplerColor "samplerColor" OpDecorate %samplerColor DescriptorSet 0 OpDecorate %samplerColor Binding 1 %10 = OpTypeImage %float 2D 0 0 0 1 Unknown %11 = OpTypeSampledImage %10 %_ptr_UniformConstant_11 = OpTypePointer UniformConstant %11 %samplerColor = OpVariable %_ptr_UniformConstant_11 UniformConstant ; 使用 %14 = OpLoad %11 %samplerColor %18 = OpLoad %v2float %inUV %21 = OpLoad %float %inLodBias %22 = OpImageSampleImplicitLod %v4float %14 %18 Bias %21
注意关于 OpImage 和 OpSampledImage 的特殊规则：
All OpSampledImage instructions must be in the same block in which their Result <id> are consumed. Result <id> from OpSampledImage instructions must not appear as operands to OpPhi instructions or OpSelect instructions, or any instructions other than the image lookup and query instructions specified to take an operand whose type is OpTypeSampledImage.
在 spvtools::opt::InstrumentPass::MovePreludeCode @ source/opt/instrument_pass.cpp (SPIRV-Tools) 中对该要求进行了处理。
Storage Buffer
14.1.7. Storage Buffer
我的一个疑惑：
1 2 3 4 5 6 layout(std430, set = 1 , binding = 0 ) readonly buffer objectBufferType { float someBeginningVar; ObjectData objects[]; float someEndingVar; } objectBuffer;
1 2 3 4 5 6 layout(std430, set = 1 , binding = 0 ) readonly buffer objectBufferType { float someBeginningVar; ObjectData objects[]; } objectBuffer;
1 2 3 4 layout(std430, set = 1 , binding = 0 ) readonly buffer objectBufferType { float someBeginningVar; } objectBuffer;
GLSL 源码：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 #version 450 layout (location = 0 ) out vec4 outFragColor; struct ObjectData { vec4 model; float moreData; vec4 padThis; }; struct WritableData { float testData; }; layout(std430, set = 1 , binding = 0 ) readonly buffer objectBufferType { ObjectData objects[]; } objectBuffer; layout(std430, set = 1 , binding = 1 ) buffer myWritableBufferType { WritableData datas[]; } writableBuffer; void main () { int index = int (gl_FragCoord.x * 1000 ); outFragColor = objectBuffer.objects[index].model; writableBuffer.datas[index].testData = 123 ; }
SPIR-V 反汇编：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 ; SPIR-V ; Version: 1.0 ; Generator: Khronos Glslang Reference Front End; 10 ; Bound: 42 ; Schema: 0 OpCapability Shader %1 = OpExtInstImport "GLSL.std.450" OpMemoryModel Logical GLSL450 OpEntryPoint Fragment %main "main" %gl_FragCoord %outFragColor OpExecutionMode %main OriginUpperLeft OpSource GLSL 450 OpName %main "main" OpName %index "index" OpName %gl_FragCoord "gl_FragCoord" OpName %outFragColor "outFragColor" OpName %ObjectData "ObjectData" OpMemberName %ObjectData 0 "model" OpMemberName %ObjectData 1 "moreData" OpMemberName %ObjectData 2 "padThis" OpName %objectBufferType "objectBufferType" OpMemberName %objectBufferType 0 "objects" OpName %objectBuffer "objectBuffer" OpName %WritableData "WritableData" OpMemberName %WritableData 0 "testData" OpName %myWritableBufferType "myWritableBufferType" OpMemberName %myWritableBufferType 0 "datas" OpName %writableBuffer "writableBuffer" OpDecorate %gl_FragCoord BuiltIn FragCoord OpDecorate %outFragColor Location 0 OpMemberDecorate %ObjectData 0 Offset 0 OpMemberDecorate %ObjectData 1 Offset 16 OpMemberDecorate %ObjectData 2 Offset 32 OpDecorate %_runtimearr_ObjectData ArrayStride 48 OpMemberDecorate %objectBufferType 0 NonWritable OpMemberDecorate %objectBufferType 0 Offset 0 OpDecorate %objectBufferType BufferBlock OpDecorate %objectBuffer DescriptorSet 1 OpDecorate %objectBuffer Binding 0 OpMemberDecorate %WritableData 0 Offset 0 OpDecorate %_runtimearr_WritableData ArrayStride 4 OpMemberDecorate %myWritableBufferType 0 Offset 0 OpDecorate %myWritableBufferType BufferBlock OpDecorate %writableBuffer DescriptorSet 1 OpDecorate %writableBuffer Binding 1 %void = OpTypeVoid %3 = OpTypeFunction %void %int = OpTypeInt 32 1 %_ptr_Function_int = OpTypePointer Function %int %float = OpTypeFloat 32 %v4float = OpTypeVector %float 4 %_ptr_Input_v4float = OpTypePointer Input %v4float %gl_FragCoord = OpVariable %_ptr_Input_v4float Input %uint = OpTypeInt 32 0 %uint_0 = OpConstant %uint 0 %_ptr_Input_float = OpTypePointer Input %float %float_1000 = OpConstant %float 1000 %_ptr_Output_v4float = OpTypePointer Output %v4float %outFragColor = OpVariable %_ptr_Output_v4float Output %ObjectData = OpTypeStruct %v4float %float %v4float %_runtimearr_ObjectData = OpTypeRuntimeArray %ObjectData %objectBufferType = OpTypeStruct %_runtimearr_ObjectData %_ptr_Uniform_objectBufferType = OpTypePointer Uniform %objectBufferType %objectBuffer = OpVariable %_ptr_Uniform_objectBufferType Uniform %int_0 = OpConstant %int 0 %_ptr_Uniform_v4float = OpTypePointer Uniform %v4float %WritableData = OpTypeStruct %float %_runtimearr_WritableData = OpTypeRuntimeArray %WritableData %myWritableBufferType = OpTypeStruct %_runtimearr_WritableData %_ptr_Uniform_myWritableBufferType = OpTypePointer Uniform %myWritableBufferType %writableBuffer = OpVariable %_ptr_Uniform_myWritableBufferType Uniform %float_123 = OpConstant %float 123 %_ptr_Uniform_float = OpTypePointer Uniform %float %main = OpFunction %void None %3 %5 = OpLabel %index = OpVariable %_ptr_Function_int Function %16 = OpAccessChain %_ptr_Input_float %gl_FragCoord %uint_0 %17 = OpLoad %float %16 %19 = OpFMul %float %17 %float_1000 %20 = OpConvertFToS %int %19 OpStore %index %20 %29 = OpLoad %int %index %31 = OpAccessChain %_ptr_Uniform_v4float %objectBuffer %int_0 %29 %int_0 %32 = OpLoad %v4float %31 OpStore %outFragColor %32 %38 = OpLoad %int %index %41 = OpAccessChain %_ptr_Uniform_float %writableBuffer %int_0 %38 %int_0 OpStore %41 %float_123 OpReturn OpFunctionEnd
总结：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 OpName %ObjectData "ObjectData" OpMemberName %ObjectData 0 "model" OpMemberName %ObjectData 1 "moreData" OpMemberName %ObjectData 2 "padThis" OpName %objectBufferType "objectBufferType" OpMemberName %objectBufferType 0 "objects" OpName %objectBuffer "objectBuffer" OpMemberDecorate %ObjectData 0 Offset 0 OpMemberDecorate %ObjectData 1 Offset 16 OpMemberDecorate %ObjectData 2 Offset 32 OpDecorate %_runtimearr_ObjectData ArrayStride 48 OpMemberDecorate %objectBufferType 0 NonWritable ; 如果可变则无此 decorate OpMemberDecorate %objectBufferType 0 Offset 0 OpDecorate %objectBufferType BufferBlock OpDecorate %objectBuffer DescriptorSet 1 OpDecorate %objectBuffer Binding 0 %ObjectData = OpTypeStruct %v4float %float %v4float %_runtimearr_ObjectData = OpTypeRuntimeArray %ObjectData ; Declare a new run-time array type. ; Its length is not known at compile time. ; See OpArrayLength for getting the Length ; of an array of this type. %objectBufferType = OpTypeStruct %_runtimearr_ObjectData %_ptr_Uniform_objectBufferType = OpTypePointer Uniform %objectBufferType %objectBuffer = OpVariable %_ptr_Uniform_objectBufferType Uniform ; 访问 ; 使用 OpAccessChain 指令，该指令是 base, indices... 格式 ; 此例子： objectBuffer[0 th][index th][0 th] 来获得 model 的指针，该指针之后可以 load / store %29 = OpLoad %int %index %31 = OpAccessChain %_ptr_Uniform_v4float %objectBuffer %int_0 %29 %int_0
Atomic 操作
https://github.com/KhronosGroup/Vulkan-Guide/blob/main/chapters/atomics.adoc
GLSL 源码：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 #version 450 layout (location = 0 ) out vec4 outFragColor; layout(std430, set = 1 , binding = 0 ) buffer statsBufferType { int totalInvocations; } statsBuffer; void main () { int globalIdx = atomicAdd(statsBuffer.totalInvocations, 1 ); outFragColor = vec4(1.0 ); }
SPIR-V 反汇编：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 ; SPIR-V ; Version: 1.0 ; Generator: Khronos Glslang Reference Front End; 10 ; Bound: 26 ; Schema: 0 OpCapability Shader %1 = OpExtInstImport "GLSL.std.450" OpMemoryModel Logical GLSL450 OpEntryPoint Fragment %main "main" %outFragColor OpExecutionMode %main OriginUpperLeft OpSource GLSL 450 OpName %main "main" OpName %globalIdx "globalIdx" OpName %statsBufferType "statsBufferType" OpMemberName %statsBufferType 0 "totalInvocations" OpName %statsBuffer "statsBuffer" OpName %outFragColor "outFragColor" OpMemberDecorate %statsBufferType 0 Offset 0 OpDecorate %statsBufferType BufferBlock OpDecorate %statsBuffer DescriptorSet 1 OpDecorate %statsBuffer Binding 0 OpDecorate %outFragColor Location 0 %void = OpTypeVoid %3 = OpTypeFunction %void %int = OpTypeInt 32 1 %_ptr_Function_int = OpTypePointer Function %int %statsBufferType = OpTypeStruct %int %_ptr_Uniform_statsBufferType = OpTypePointer Uniform %statsBufferType %statsBuffer = OpVariable %_ptr_Uniform_statsBufferType Uniform %int_0 = OpConstant %int 0 %_ptr_Uniform_int = OpTypePointer Uniform %int %int_1 = OpConstant %int 1 %uint = OpTypeInt 32 0 %uint_1 = OpConstant %uint 1 %uint_0 = OpConstant %uint 0 %float = OpTypeFloat 32 %v4float = OpTypeVector %float 4 %_ptr_Output_v4float = OpTypePointer Output %v4float %outFragColor = OpVariable %_ptr_Output_v4float Output %float_1 = OpConstant %float 1 %25 = OpConstantComposite %v4float %float_1 %float_1 %float_1 %float_1 %main = OpFunction %void None %3 %5 = OpLabel %globalIdx = OpVariable %_ptr_Function_int Function %14 = OpAccessChain %_ptr_Uniform_int %statsBuffer %int_0 %19 = OpAtomicIAdd %int %14 %uint_1 %uint_0 %int_1 ; Pointer = %14 ; Memory Scope = %uint_1 = 1 ; => Scope is the current device ; Semantics = %uint_0 = 0 ; => None (relaxed) ; Value = %uint_1 = 1 OpStore %globalIdx %19 OpStore %outFragColor %25 OpReturn OpFunctionEnd
Memory Scope: https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#Scope_-id-
Coming soon
Matrix 类型
导数 dFdx / dFdy & discard
Group Ops