Make shader inputs/outputs only statically indexable

Previously we used a Reactor array of SIMD variables to store shader
inputs and outputs. This allows for dynamic indexing but that's not
needed.

LLVM has difficulties performing Scalar-Replacement-of-Aggregates (SROA)
on this array, resulting in unnecessary initialization of all elements
and presumably other loads and stores it could optimize.

Bug: b/219942708
Change-Id: I4844b184db84ba2183e14c1f0b88b04a553a5626
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/63028
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>

src/Pipeline/SpirvShader.cpp

diff --git a/src/Pipeline/SpirvShader.cpp b/src/Pipeline/SpirvShader.cpp
index 726e457..3334677 100644
--- a/src/Pipeline/SpirvShader.cpp
+++ b/src/Pipeline/SpirvShader.cpp
@@ -927,7 +927,7 @@
 		VisitInterface(resultId,
 		               [&userDefinedInterface](Decorations const &d, AttribType type) {
 			               // Populate a single scalar slot in the interface from a collection of decorations and the intended component type.
-			               auto scalarSlot = (d.Location << 2) | d.Component;
+			               int32_t scalarSlot = (d.Location << 2) | d.Component;
 			               ASSERT(scalarSlot >= 0 &&
 			                      scalarSlot < static_cast<int32_t>(userDefinedInterface.size()));