HLSL 编译器省略了关键语句

Question

我有这个遍历二叉树的计算着色器。它曾经与单独安装的 DirectX SDK(六月(一起使用编译器 #43 正常工作。

然而，编译器 #46 和 #47(分别来自 Windows SDK 8.0 和 8.1(似乎省略了两行非常关键的代码，即着色器在圆圈中运行，一遍又一遍地检查相同的树节点，直到 Windows 重新启动图形驱动程序(通过查看反汇编进行验证(。

下面是演示此行为的最小代码示例：

#define LEFT_PROCESSED  1
#define RIGHT_PROCESSED 2
struct Node
{
float4 min;
float4 max;
int left;
int right;
int parent;
int flags;
};
RWStructuredBuffer<Node> tree: register(u0);
bool TreeSearch()
{
Node node = tree[0];
int nodeId = 0;
int statusStack[40];
int stackSize = 0;
statusStack[0] = 0;
while (true)
{
if (!(statusStack[stackSize] & LEFT_PROCESSED))
{
statusStack[stackSize] |= LEFT_PROCESSED;
++stackSize;
statusStack[stackSize] = 0;
nodeId = node.left;
node = tree[nodeId];
continue;
}
if (!(statusStack[stackSize] & RIGHT_PROCESSED))
{
statusStack[stackSize] |= RIGHT_PROCESSED; // this line
++stackSize;
statusStack[stackSize] = 0;                // and this line
nodeId = node.right;
node = tree[nodeId];
continue;
}
if (node.parent != -1)
{
--stackSize;
nodeId = node.parent;
node = tree[nodeId];
}
else
return false;
}
return false;
}
[numthreads(32, 1, 1)]
void CSSearch(uint2 dispatchThreadId: SV_DispatchThreadID)
{
TreeSearch();
}

以及相应的组件：

cs_5_0
dcl_globalFlags refactoringAllowed
dcl_uav_structured u0, 48
dcl_temps 3
dcl_indexableTemp x0[40], 4
dcl_thread_group 32, 1, 1
ld_structured_indexable(structured_buffer, stride=48)(mixed,mixed,mixed,mixed) r0.xyz, l(0), l(32), u0.xyzx
mov x0[0].x, l(0)
mov r1.xyz, r0.yzxy
mov r0.w, l(0)
loop 
mov r1.w, x0[r0.w + 0].x
and r2.x, r1.w, l(1)
if_z r2.x
or r1.w, r1.w, l(1)       // here's the first one in the LEFT branch
mov x0[r0.w + 0].x, r1.w  //
iadd r1.w, r0.w, l(1)
mov x0[r1.w + 0].x, l(0)  // and the second one
ld_structured_indexable(structured_buffer, stride=48)(mixed,mixed,mixed,mixed) r2.xyz, r1.z, l(32), u0.yzxx
mov r1.xyz, r2.xyzx
mov r0.w, r1.w
continue 
endif 
mov r1.w, x0[r0.w + 0].x   // why is there nothing in the RIGHT branch?
and r1.w, r1.w, l(2)
if_z r1.w
iadd r1.w, r0.w, l(1)
ld_structured_indexable(structured_buffer, stride=48)(mixed,mixed,mixed,mixed) r2.xyz, r1.x, l(32), u0.yzxx
mov r1.xyz, r2.xyzx
mov r0.w, r1.w
continue 
endif 
ine r1.w, r1.y, l(-1)
if_nz r1.w
iadd r0.w, r0.w, l(-1)
ld_structured_indexable(structured_buffer, stride=48)(mixed,mixed,mixed,mixed) r1.xyz, r1.y, l(32), u0.yzxx
else 
break 
endif 
endloop 
ret 

当我省略第一个continue时，它会生成这两行的代码，但随后它也被破坏了。

知道如何让较新的编译器生成该代码吗？

Answer 1

请注意：我不熟悉 GPU 编程，不确定这是编译器的错误还是代码的错误。以下只是一个解决方法。

您可以使用显式变量来模拟continue行为，希望编译器不会妨碍：

bool TreeSearch()
{
Node node = tree[0];
int nodeId = 0;
int statusStack[40];
int stackSize = 0;
statusStack[0] = 0; 
while (stackSize < 10) // Changed to make it compile.
{
int shouldContinue = 1;
if (!(statusStack[stackSize] & LEFT_PROCESSED))
{
statusStack[stackSize] |= LEFT_PROCESSED;
++stackSize;
statusStack[stackSize] = 0;
nodeId = node.left;
node = tree[nodeId];
shouldContinue = 0;
}
if (shouldContinue && 
!(statusStack[stackSize] & RIGHT_PROCESSED))
{
statusStack[stackSize] |= RIGHT_PROCESSED; // this line
++stackSize;
statusStack[stackSize] = 0;                // and this line
nodeId = node.right;
node = tree[nodeId];
shouldContinue = 0;
}
if (shouldContinue)
{ 
if (node.parent != -1)
{
--stackSize;
nodeId = node.parent;
node = tree[nodeId];
}
else
return false;
}
}
return false;
}

反汇编输出似乎并不缺少原始代码段中缺少的任何操作。不过，这可能会产生开销。

链接： http://shader-playground.timjones.io/6abdc64cdf98e1840a3b38c629b4e217