SPIRV: Fix performance issue when handling large arrays. (#4064)

* SPIRV: Fix performance issue when handling large arrays.

* Add test for packing.

* Fix clang.

1 files changed, 29 insertions, 0 deletions

diff --git a/tests/spirv/large-struct-pack.slang b/tests/spirv/large-struct-pack.slang
new file mode 100644
index 000000000..df15ac67c
--- /dev/null
+++ b/tests/spirv/large-struct-pack.slang
@@ -0,0 +1,29 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv -emit-spirv-directly -profile glsl_460
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-vk -compute
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-cpu -compute
+
+// Check that when generating spirv directly, we use a loop
+// to copy large arrays in a local variable to a buffer, instead of emitting
+// unrolled code that reads each element of the array individually.
+
+struct WorkData
+{
+    int B[1024];
+};
+
+//TEST_INPUT:set resultBuffer = out ubuffer(data=[0 0 0 0], stride=4, count=1024)
+RWStructuredBuffer<WorkData> resultBuffer;
+
+// CHECK: OpLoopMerge
+// CHECK: OpLoopMerge
+
+// BUF: 0
+// BUF: 1
+[numthreads(1, 1, 1)]
+void computeMain(uint3 tid: SV_DispatchThreadID)
+{
+    WorkData wd;
+    for (int i = 0; i < 1024; i++)
+        wd.B[i] = i;
+    resultBuffer[0] = wd;
+}