Fix redundant decorations in IRParam (#4964)

* Fix redundant decorations in IRParam

Closes #4922

The problem was that same decorations were added to an IRParam multiple
times while running `specializeIRForEntryPoint()`.

`cloneGlobalValueWithCodeCommon()` kept cloning decorations for the
params that were already processed.

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/bugs/gh-4922-nointerpolation.slang b/tests/bugs/gh-4922-nointerpolation.slang
new file mode 100644
index 000000000..3619aae0b
--- /dev/null
+++ b/tests/bugs/gh-4922-nointerpolation.slang
@@ -0,0 +1,15 @@
+//TEST:SIMPLE(filecheck=HLSL): -target hlsl -entry main
+//TEST:SIMPLE(filecheck=GLSL): -target glsl -entry main
+
+// This test checks if `nointerpolation` is emitted more than once
+//HLSL-NOT:nointerpolation nointerpolation 
+//GLSL-NOT:flat flat
+
+[shader("pixel")]
+void main(out float4 SV_Target : SV_Target, const in nointerpolation float4 color : color)
+{
+    for (int i = 0; i < 10; ++i)
+    {}
+
+    SV_Target = color;
+}