[DirectX] Initializing An HLSL Vector With A Function Call Results In An Assert
Introduction
In this article, we will explore a specific issue related to DirectX HLSL (High-Level Shading Language) vector initialization using function calls. The problem arises when attempting to initialize a vector with a function call, resulting in an assert in the CodeGenFunction::getOrCreateOpaqueRValueMapping function.
Background
HLSL is a programming language used for writing shaders, which are small programs that run on the GPU (Graphics Processing Unit). Shaders are used to perform various tasks such as lighting, texturing, and other visual effects in graphics rendering.
The Issue
The issue at hand is related to the following code snippet:
uint GetInputState(uint x) {
return x;
}
export uint4 fn() {
uint4 counter = { GetInputState(0), GetInputState(1), GetInputState(2), GetInputState(3) };
return counter;
}
When we attempt to compile this code, we encounter an assert in the CodeGenFunction::getOrCreateOpaqueRValueMapping function.
Crash Dump
The crash dump is as follows:
* frame #0: 0x0000000103eeb77c clang-dxc`clang::CodeGen::CodeGenFunction::getOrCreateOpaqueRValueMapping(this=0x000000016fdf1298, e=0x000000012c91a6f8) at CGExpr.cpp:5664:3
frame #1: 0x0000000103f87a80 clang-dxc`(anonymous namespace)::ScalarExprEmitter::VisitOpaqueValueExpr(this=0x000000016fdee048, E=0x000000012c91a6f8) at CGExprScalar.cpp:545:16
frame #2: 0x0000000103f814cc clang-dxc`clang::StmtVisitorBase<std::__1::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(this=0x000000016fdee048, S=0x000000012c91a6f8) at StmtNodes.inc:196:1
frame #3: 0x0000000103f77b3c clang-dxc`(anonymous namespace)::ScalarExprEmitter::Visit(this=0x000000016fdee048, E=0x000000012c91a6f8) at CGExprScalar.cpp:449:52
frame #4: 0x0000000103f88fb8 clang-dxc`(anonymous namespace)::ScalarExprEmitter::VisitInitListExpr(this=0x000000016fdee048, E=0x000000012c91a7b8) at CGExprScalar.cpp:2143:19
frame #5: 0x0000000103f816e8 clang-dxc`clang::StmtVisitorBase<std::__1::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(this=0x000000016fdee048, S=0x000000012c91a7b8) at StmtNodes.inc:358:1
frame #6: 0x0000000103f77b3c clang-dxc`(anonymous namespace)::ScalarExprEmitter::Visit(this=0x000000016fdee048, E=0x000012c91a7b8) at CGExprScalar.cpp:449:52
frame #7: 0x0000000103f77920 clang-dxc`clang::CodeGen::CodeGenFunction::EmitScalarExpr(this=0x000000016fdf1298, E=0x000000012c91a7b8, IgnoreResultAssign=false) at CGExprScalar.cpp:5748:8
frame #8: 0x0000000103e89e18 clang-dxc`clang::CodeGen::CodeGenFunction::EmitScalarInit(this=0x000000016fdf1298, init=0x000000012c91a7b8, D=0x000000012c91a2b0, lvalue=LValue @ 0x000000016fdeeb28, capturedByInit=false) at CGDecl.cpp:784:15
frame #9: 0x0000000103e91518 clang-dxc`clang::CodeGen::CodeGenFunction::EmitExprAsInit(this=0x000000016fdf1298, init=0x000000012c91a7b8, D=0x000000012c91a2b0, lvalue=LValue @ 0x000000016fdef020, capturedByInit=false) at CGDecl.cpp:2093:5
frame #10: 0x0000000103e8dd30 clang-dxc`clang::CodeGen::CodeGenFunction::EmitAutoVarInit(this=0x000000016fdf1298, emission=0x000000016fdef410) at CGDecl.cpp:2045:12
frame #11: 0x0000000103e885a4 clang-dxc`clang::CodeGen::CodeGenFunction::EmitAutoVarDecl(this=0x000000016fdf1298, D=0x000000012c91a2b0) at CGDecl.cpp:1333:3
frame #12: 0x0000000103e8794c clang-dxc`clang::CodeGen::CodeGenFunction::EmitVarDecl(this=0x000000016fdf1298, D=0x000000012c91a2b0) at CGDecl.cpp:225:10
frame #13: 0x0000000103e870bc clang-dxc`clang::CodeGen::CodeGenFunction::EmitDecl(this=0x000000016fdf1298, D=0x000000012c91a2b0, EvaluateConditionDecl=true) at CGDecl.cpp:166:5
frame #14: 0x00000001041f0304 clang-dxc`clang::CodeGen::CodeGenFunction::EmitDeclStmt(this=0x000000016fdf1298, S=0x000000012c91a830) at CGStmt.cpp:1674:5
frame #15: 0x00000001041e6bbc clang-dxc`clang::CodeGen::CodeGenFunction::EmitSimpleStmt(this=0x000000016fdf1298, S=0x000000012c91a830, Attrs=ArrayRef<const clang::Attr *> @ 0x000000016fdef6f0) at CGStmt.cpp:515:5
frame #16: 0x00000001041e5874 clang-dxc`clang::CodeGen::CodeGenFunction::EmitStmt(this=0x000000016fdf1298, S=0x000000012c91a830, Attrs=ArrayRef<const::Attr *> @ 0x000000016fdef860) at CGStmt.cpp:65:7
frame #17: 0x00000001041f1958 clang-dxc`clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(this=0x000000016fdf1298, S=0x000000012c91c2e0, GetLast=false, AggSlot=AggValueSlot @ 0x000000016fdefb38) at CGStmt.cpp:622:7
frame #18: 0x00000001041f021c clang-dxc`clang::CodeGen::CodeGenFunction::EmitCompoundStmt(this=0x000000016fdf1298, S=0x000000012c91c2e0, GetLast=false, AggSlot=AggValueSlot @ 0x000000016fdefcc8) at CGStmt.cpp:573:10
frame #19: 0x00000001041e6ba4 clang-dxc`clang::CodeGen::CodeGenFunction::EmitSimpleStmt(this=0x000000016fdf1298, S=0x000000012c91c2e0, Attrs=ArrayRef<const clang::Attr *> @ 0x000000016fdefc80) at CGStmt.cpp:512:5
frame #20: 0x00000001041e5874 clang-dxc`clang::CodeGen::CodeGenFunction::EmitStmt(this=0x000000016fdf1298, S=0x000000012c91c2e0, Attrs=ArrayRef<const clang::Attr *> @ 0x000000016fdefdf0) at CGStmt.cpp:65:7
frame #21: 0x00000001041e73f8 clang-dxc`clang::CodeGen::CodeGenFunction::EmitIfStmt(this=0x000000016fdf1298, S=0x000000012c91c340) at CGStmt.cpp:974:5
frame #22: 0x00000001041e5b64 clang-dxc`clang::CodeGen::CodeGenFunction::EmitStmt(this=0x000000016fdf1298, S=0x000000012c91c340, Attrs=ArrayRef<const clang::Attr *> @ 0x000000016fdf02a0) at CGStmt.cpp:157:32
frame #23: 0x00000001041f1958 clang-dxc`clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(this=0x000000016fdf<br/>
**DirectX HLSL Vector Initialization with Function Call Results in Assert: Q&A**
================================================================================
**Q: What is the issue with the code snippet provided?**
---------------------------------------------------
A: The issue with the code snippet is that it attempts to initialize a vector with a function call, which results in an assert in the CodeGenFunction::getOrCreateOpaqueRValueMapping function.
**Q: What is the CodeGenFunction::getOrCreateOpaqueRValueMapping function?**
------------------------------------------------------------------------
A: The CodeGenFunction::getOrCreateOpaqueRValueMapping function is a part of the Clang compiler's code generation functionality. It is responsible for creating a mapping between a source expression and a target expression in the generated code.
**Q: Why does the assert occur in this function?**
------------------------------------------------
A: The assert occurs in this function because the code generation process is unable to create a valid mapping between the source expression (the function call) and the target expression (the vector initialization).
**Q: What is the cause of this issue?**
--------------------------------------
A: The cause of this issue is that the code generation process is unable to handle the function call as a valid expression for initializing a vector.
**Q: How can this issue be resolved?**
--------------------------------------
A: This issue can be resolved by modifying the code to use a different initialization method, such as using a constant value or a different function call that can be handled by the code generation process.
**Q: What are some possible solutions to this issue?**
---------------------------------------------------
A: Some possible solutions to this issue include:
* Using a constant value to initialize the vector, such as `uint4 counter = { 0, 1, 2, 3 };`
* Using a different function call that can be handled by the code generation process
* Modifying the code generation process to handle function calls as valid expressions for initializing vectors
**Q: How can I debug this issue?**
-----------------------------------
A: To debug this issue, you can use a debugger to step through the code generation process and identify the point at which the assert occurs. You can also use print statements or other debugging tools to gather more information about the code generation process.
**Q: What are some best practices for avoiding this issue?**
---------------------------------------------------------
A: Some best practices for avoiding this issue include:
* Using constant values to initialize vectors whenever possible
* Avoiding function calls that may not be handled by the code generation process
* Testing the code generation process thoroughly to identify any potential issues
**Q: Can this issue be fixed in the Clang compiler?**
------------------------------------------------
A: Yes, this issue can be fixed in the Clang compiler by modifying the code generation process to handle function calls as valid expressions for initializing vectors. This may involve updating the CodeGenFunction::getOrCreateOpaqueRValueMapping function or other related code generation functions.