[mandatory-inline] Move the creation of the inliner and bailing upon knowing that inlining will fail, before any side-effect having work occurs.

rdar://31521023

Author: gottesmm

include/swift/SIL/SILInstruction.h

@@ -6529,6 +6529,16 @@ class ApplySite {
     FOREACH_IMPL_RETURN(getSubstitutions());
   }
 
+  /// Return a begin iterator for the substitution array.
+  auto subs_begin() const -> decltype(getSubstitutions().begin()) {
+    return getSubstitutions().begin();
+  }
+
+  /// Return an end iterator for the substitution array.
+  auto subs_end() const -> decltype(getSubstitutions().end()) {
+    return getSubstitutions().end();
+  }
+
   /// The arguments passed to this instruction.
   MutableArrayRef<Operand> getArgumentOperands() const {
     FOREACH_IMPL_RETURN(getArgumentOperands());

lib/SILOptimizer/Mandatory/MandatoryInlining.cpp

@@ -418,6 +418,35 @@ runOnFunctionRecursively(SILFunction *F, FullApplySite AI,
         return false;
       }
 
+      // Create our initial list of substitutions.
+      llvm::SmallVector<Substitution, 16> ApplySubs(InnerAI.subs_begin(),
+                                                    InnerAI.subs_end());
+
+      // Then if we have a partial_apply, add any additional subsitutions that
+      // we may require to the end of the list.
+      if (PAI) {
+        copy(PAI->getSubstitutions(), std::back_inserter(ApplySubs));
+      }
+
+      SILOpenedArchetypesTracker OpenedArchetypesTracker(F);
+      F->getModule().registerDeleteNotificationHandler(
+          &OpenedArchetypesTracker);
+      // The callee only needs to know about opened archetypes used in
+      // the substitution list.
+      OpenedArchetypesTracker.registerUsedOpenedArchetypes(
+          InnerAI.getInstruction());
+      if (PAI) {
+        OpenedArchetypesTracker.registerUsedOpenedArchetypes(PAI);
+      }
+
+      SILInliner Inliner(*F, *CalleeFunction,
+                         SILInliner::InlineKind::MandatoryInline, ApplySubs,
+                         OpenedArchetypesTracker);
+      if (!Inliner.canInlineFunction(InnerAI)) {
+        I = InnerAI.getInstruction()->getIterator();
+        continue;
+      }
+
       // Inline function at I, which also changes I to refer to the first
       // instruction inlined in the case that it succeeds. We purposely
       // process the inlined body after inlining, because the inlining may
@@ -456,31 +485,6 @@ runOnFunctionRecursively(SILFunction *F, FullApplySite AI,
       else
         I = ApplyBlock->end();
 
-      std::vector<Substitution> ApplySubs(InnerAI.getSubstitutions());
-
-      if (PAI) {
-        auto PAISubs = PAI->getSubstitutions();
-        ApplySubs.insert(ApplySubs.end(), PAISubs.begin(), PAISubs.end());
-      }
-
-      SILOpenedArchetypesTracker OpenedArchetypesTracker(F);
-      F->getModule().registerDeleteNotificationHandler(
-          &OpenedArchetypesTracker);
-      // The callee only needs to know about opened archetypes used in
-      // the substitution list.
-      OpenedArchetypesTracker.registerUsedOpenedArchetypes(InnerAI.getInstruction());
-      if (PAI) {
-        OpenedArchetypesTracker.registerUsedOpenedArchetypes(PAI);
-      }
-
-      SILInliner Inliner(*F, *CalleeFunction,
-                         SILInliner::InlineKind::MandatoryInline,
-                         ApplySubs, OpenedArchetypesTracker);
-      if (!Inliner.canInlineFunction(InnerAI)) {
-        I = InnerAI.getInstruction()->getIterator();
-        continue;
-      }
-
       Inliner.inlineFunction(InnerAI, FullArgs);
 
       // We were able to inline successfully. Remove the apply.