Disable deployment target specific optimizations for inlinable functions

[eeckstein]

The specified deployment target only applies to the currently compiled module, but not to any client modules, which use inlinable functions from the current module.
Therefore, optimizations which depend on the deployment target must not optimize inlinable functions, except they run after the module has been serialized.

• constant folding of availability checks
• simplification of ARC operations on immortal objects (which depends on the 5.1 runtime)

rdar://88117184

The same thing needs to be done in Sema. There is already a PR for this: #33855, but unfortunately currently reverted.

[eeckstein]

@swift-ci test

[eeckstein]

@swift-ci test

[aschwaighofer]

We also need to fix availability guarded prespecialization uses. Something like:

--- a/lib/SILOptimizer/Utils/Generics.cpp
+++ b/lib/SILOptimizer/Utils/Generics.cpp
@@ -2512,7 +2512,21 @@ usePrespecialized(SILOptFunctionBuilder &funcBuilder, ApplySite apply,
     auto specializationAvail = SA->getAvailability();
     auto &ctxt = funcBuilder.getModule().getSwiftModule()->getASTContext();
     auto deploymentAvail = AvailabilityContext::forDeploymentTarget(ctxt);
-    auto currentFnAvailability = apply.getFunction()->getAvailabilityForLinkage();
+    auto currentFn = apply.getFunction();
+    auto isInlinableCtxt = currentFn->getResilienceExpansion()
+      == ResilienceExpansion::Minimal;
+    auto currentFnAvailability = currentFn->getAvailabilityForLinkage();
+
+    // If we are in an inlineable function we can't use the specialization except
+    // it the inlinable function itself has availability we can used.
+    if (currentFnAvailability.isAlwaysAvailable() &&
+        isInlinableCtxt) {
+      continue;
+    }
+    else if (isInlinableCtxt) {
+      deploymentAvail = currentFnAvailability;
+    }
+
     if (!currentFnAvailability.isAlwaysAvailable() &&
         !deploymentAvail.isContainedIn(currentFnAvailability))
       deploymentAvail = currentFnAvailability;

[aschwaighofer]

Knitpick. Should we move this earlier in this function before the other checks.

[aschwaighofer]

lgtm.

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - d38bb040474b6b2929cffd3f9b069c50c1607889

[eeckstein]

@swift-ci smoke test

[eeckstein]

@swift-ci smoke test