Implement spec const for generic parameter (#7121)

Close #6840.

This PR add supports to use specialize constant in generic parameter, and that parameter can also be used as array size, e.g. following code should work:

```
struct MyStruct<let N: int> { float buffer[N]; }
MyStruct<SpecConstVar> s;
```

- Loose the restriction from Link-Time to SpecializationConstant when extract generic argument
- Tweak the logic of how we decide whether a inst is hoistable. Besides checking existing hoistable flag of each 
  IRInst, when we detect a IRInst's type is SpecConstRateType, we will treat that inst hoistable. Because IRInst in 
  global scope can be deduplicated, and every SpecConstRateType inst should be in the global scope or IRGeneric 
  scope (which will be at global scope after specialization).
- Remove the SpecConstIntVal to IRInst map in IR lowering logic, because we already have way to deduplicate the 
  global scope IR.

1 files changed, 53 insertions, 0 deletions

diff --git a/tests/spirv/spec-constant-generic.slang b/tests/spirv/spec-constant-generic.slang
new file mode 100644
index 000000000..65eed2810
--- /dev/null
+++ b/tests/spirv/spec-constant-generic.slang
@@ -0,0 +1,53 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+//TEST(compute, vulkan):COMPARE_COMPUTE(filecheck-buffer=BUF):-vk -output-using-type
+
+// CHECK: %[[C0:[0-9A-Za-z_]+]] = OpSpecConstant %int 32
+// CHECK: %[[C1:[0-9A-Za-z_]+]] = OpSpecConstant %int 2
+// CHECK: %[[COP0:[0-9A-Za-z_]+]] = OpSpecConstantOp %int SDiv %[[C0]] %[[C1]]
+// CHECK: %[[ARR_TYPE:[0-9A-Za-z_]+]] = OpTypeArray %float %[[COP0]]
+// CHECK: %[[PT_TYPE:[0-9A-Za-z_]+]] = OpTypePointer Function %[[ARR_TYPE]]
+
+[SpecializationConstant]
+const int constValue0 = 32;
+
+[SpecializationConstant]
+const int constValue1 = 2;
+
+//TEST_INPUT:ubuffer(data=[0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+void func(out float buffer[constValue0 / constValue1])
+{
+    for (uint i = 0; i < constValue0 / constValue1; i++)
+    {
+        buffer[i] = i;
+    }
+}
+
+struct MyStruct<let N: int>
+{
+    float buffer[N / constValue1];
+}
+
+[shader("compute")]
+[numthreads(1, 1, 1)]
+void computeMain()
+{
+    // This test checks we can use spec constants for generic arguments, and also
+    // we can show that the array size is computed correctly.
+    // The function call shows that the two arrays are the same type.
+    MyStruct<constValue0> s;
+    // CHECK: OpVariable %[[PT_TYPE]] Function
+
+    func(s.buffer);
+
+    float temp = 0.0f;
+    for (uint i = 0; i < constValue0 / constValue1; i++)
+    {
+        temp += s.buffer[i] * 2;
+    }
+
+    // Result will be (0 + localConst-1) * localConst = 15 * 16 = 240
+    outputBuffer[0] = temp;
+    // BUF: 240
+}