Fix Varying Variable Location Assignments With Hull Shaders (#4915)

* Fix Varying Variable Location Assignments With Hull Shaders

Fixes: #4913
Fixes: #4540

Changes:
1. Added `kIROp_ControlBarrier` to HLSL/GLSL emitting.
2. Added a method to track 'used' and 'unused' varyings for when legalizing GLSL. This allows us to assign correct offsets to automatically added varyings
    * Added a `ZeroLSB` check to UIntSet for this purpose

* add missing return

* code comment adjustment

* cleanup

* comment and HLSL controlBarrier mistake

* assume space for glsl/spriv varying is irrelevant

1 files changed, 21 insertions, 0 deletions

diff --git a/source/core/slang-uint-set.cpp b/source/core/slang-uint-set.cpp
index ba71254e1..457915449 100644
--- a/source/core/slang-uint-set.cpp
+++ b/source/core/slang-uint-set.cpp
@@ -3,6 +3,27 @@
 namespace Slang
 {
 
+Index UIntSet::getLSBZero()
+{
+    uint64_t offset = 0;
+    for (Element& element : this->m_buffer)
+    {
+        // Flip all bits so bitscanForward can find a 0 bit
+        Element flippedElement = ~element;
+
+        // continue if we don't have 0 bits
+        if (flippedElement == 0)
+        {
+            offset += sizeof(Element) * 8;
+            continue;
+        }
+
+        // Get LSBZero of current Block, add with offset
+        return bitscanForward(flippedElement) + offset;
+    }
+    return offset;
+}
+
 UIntSet& UIntSet::operator=(UIntSet&& other)
 {
     m_buffer = _Move(other.m_buffer);