PerformanceInliner: add the @_semantics("optimize.sil.inline.aggressive") attribute to enable inlining into large functions.

This attribute overrides the limit of maximum number of basic blocks in the caller.

docs/HighLevelSILOptimizations.rst

@@ -412,6 +412,11 @@ optimize.sil.specialize.owned2guarantee.never
   Disable function signature optimization which converts an "owned" to a
   "guaranteed" function parameter.
 
+optimize.sil.inline.aggressive
+
+  Inlines into this function more aggressively than it would be done without
+  this attribute.
+
 Availability checks
 ~~~~~~~~~~~~~~~~~~~
 

include/swift/AST/SemanticAttrs.def

@@ -75,6 +75,8 @@ SEMANTICS_ATTR(OPTIMIZE_SIL_SPECIALIZE_GENERIC_SIZE_NEVER,
           "optimize.sil.specialize.generic.size.never")
 SEMANTICS_ATTR(OPTIMIZE_SIL_SPECIALIZE_OWNED2GUARANTEE_NEVER,
           "optimize.sil.specialize.owned2guarantee.never")
+SEMANTICS_ATTR(OPTIMIZE_SIL_INLINE_AGGRESSIVE,
+          "optimize.sil.inline.aggressive")
 
 // To be used on a nominal type declaration.
 // Assumes that a class (or class references inside a nominal type) are immortal.

lib/SILOptimizer/Transforms/PerformanceInliner.cpp

@@ -1153,7 +1153,8 @@ void SILPerformanceInliner::collectAppliesToInline(
         // but we /do/ inline any inline_always functions remaining.
         if (NumCallerBlocks > OverallCallerBlockLimit &&
             // Still allow inlining of small functions.
-            !hasMaxNumberOfBasicBlocks(Callee, 8)) {
+            !hasMaxNumberOfBasicBlocks(Callee, 8) &&
+            !Caller->hasSemanticsAttr(semantics::OPTIMIZE_SIL_INLINE_AGGRESSIVE)) {
           continue;
         }