Implement bitcast for 64-bit date type (#5895)

Close #5470

* implement bitcast for 64-bit date type
* Move 'ensurePrelude' to base class to remove duplication
* Assert on 'double' type for Metal target, as Metal doesn't have 'double' support

2 files changed, 48 insertions, 0 deletions

diff --git a/tests/compute/bitcast-64bit.slang b/tests/compute/bitcast-64bit.slang
new file mode 100644
index 000000000..410fa768a
--- /dev/null
+++ b/tests/compute/bitcast-64bit.slang
@@ -0,0 +1,43 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -emit-spirv-via-glsl -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -d3d12 -profile cs_6_6 -use-dxil -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-cuda -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-cpu -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0 0 0 0], stride=4):out,name=gOutputBuffer
+RWStructuredBuffer<uint64_t> gOutputBuffer;
+
+int64_t icast(double x)
+{
+    return bit_cast<int64_t>(x);
+}
+
+int64_t icast(uint64_t x)
+{
+    return bit_cast<int64_t>(x);
+}
+
+uint64_t ucast(double x)
+{
+    return bit_cast<uint64_t>(x);
+}
+
+uint64_t ucast(int64_t x)
+{
+    return bit_cast<uint64_t>(x);
+}
+
+[numthreads(1, 1, 1)]
+[shader("compute")]
+void computeMain()
+{
+    double t1 = -1.0;
+    uint64_t t2 = 2;
+    gOutputBuffer[0] = icast(t1);    // 0xBFF0000000000000 => 13830554455654793216
+    gOutputBuffer[1] = icast(t2);    // 0x0000000000000002 => 2
+
+    double t3 = 3.0;
+    int64_t t4 = -4;
+    gOutputBuffer[2] = ucast(t3);   // 0x4008000000000000 => 4613937818241073152
+    gOutputBuffer[3] = ucast(t4);   // 0xFFFFFFFFFFFFFFFC => 18446744073709551612
+}
diff --git a/tests/compute/bitcast-64bit.slang.expected.txt b/tests/compute/bitcast-64bit.slang.expected.txt
new file mode 100644
index 000000000..cb9a9f87d
--- /dev/null
+++ b/tests/compute/bitcast-64bit.slang.expected.txt
@@ -0,0 +1,5 @@
+type: uint64_t
+13830554455654793216
+2
+4613937818241073152
+18446744073709551612