OSSA: simplify-cfg support for trivial block arguments.

Enable most simplify-cfg optimizations as long as the block arguments
have trivial types. Enable most simplify CFG unit tests cases.

This massively reduces the size of the CFG during OSSA passes.

Test cases that aren't supported in OSSA yet have been moved to a
separate test file for disabled OSSA tests,

Full simplify-cfg support is currently blocked on OSSA utilities which
I haven't checked in yet.

Author: atrick

include/swift/SILOptimizer/Utils/InstOptUtils.h

@@ -273,9 +273,15 @@ SILValue getConcreteValueOfExistentialBoxAddr(SILValue addr,
 /// - a type of the return value is a subclass of the expected return type.
 /// - actual return type and expected return type differ in optionality.
 /// - both types are tuple-types and some of the elements need to be casted.
+///
+/// \p usePoints is required when \p value has guaranteed ownership. It must be
+/// the last users of the returned, casted value. A usePoint cannot be a
+/// BranchInst (a phi is never the last guaranteed user). \p builder's current
+/// insertion point must dominate all \p usePoints.
 std::pair<SILValue, bool /* changedCFG */>
 castValueToABICompatibleType(SILBuilder *builder, SILLocation Loc,
-                             SILValue value, SILType srcTy, SILType destTy);
+                             SILValue value, SILType srcTy, SILType destTy,
+                             ArrayRef<SILInstruction *> usePoints);
 /// Peek through trivial Enum initialization, typically for pointless
 /// Optionals.
 ///

lib/SIL/IR/SILFunctionType.cpp

@@ -4319,6 +4319,9 @@ TypeConverter::getLoweredFormalTypes(SILDeclRef constant,
 // match exactly.
 // TODO: More sophisticated param and return ABI compatibility rules could
 // diverge.
+//
+// Note: all cases recognized here must be handled in the SILOptimizer's
+// castValueToABICompatibleType().
 static bool areABICompatibleParamsOrReturns(SILType a, SILType b,
                                             SILFunction *inFunction) {
   // Address parameters are all ABI-compatible, though the referenced

lib/SILGen/SILGenThunk.cpp

@@ -260,7 +260,6 @@ SILGenModule::getOrCreateForeignAsyncCompletionHandlerImplFunction(
       auto flagIndex = convention.completionHandlerFlagParamIndex();
 
       FuncDecl *resumeIntrinsic;
-      Type replacementTypes[] = {resumeType};
 
       SILBasicBlock *returnBB = nullptr;
       if (errorIndex) {