SILVerifier: remove the unused -verify-skip-unreachable-must-be-last option

It had no effect, because such SIL is never generated anyway.

Author: eeckstein

lib/SIL/Verifier/SILVerifier.cpp

@@ -52,14 +52,6 @@ using namespace swift::silverifier;
 
 using Lowering::AbstractionPattern;
 
-// This flag is used only to check that sil-combine can properly
-// remove any code after unreachable, thus bringing SIL into
-// its canonical form which may get temporarily broken during
-// intermediate transformations.
-static llvm::cl::opt<bool> SkipUnreachableMustBeLastErrors(
-                              "verify-skip-unreachable-must-be-last",
-                              llvm::cl::init(false));
-
 // This flag controls the default behaviour when hitting a verification
 // failure (abort/exit).
 static llvm::cl::opt<bool> AbortOnFailure(
@@ -1026,10 +1018,8 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
                 "Non-terminators cannot be the last in a block");
       }
     } else {
-      // Skip the check for UnreachableInst, if explicitly asked to do so.
-      if (!isa<UnreachableInst>(I) || !SkipUnreachableMustBeLastErrors)
-        require(&*BB->rbegin() == I,
-                "Terminator must be the last in block");
+      require(&*BB->rbegin() == I,
+              "Terminator must be the last in block");
     }
 
     // Verify that all of our uses are in this function.

test/SILOptimizer/sil_combine.sil

@@ -1,4 +1,4 @@
-// RUN: %target-sil-opt -enable-objc-interop -enforce-exclusivity=none -enable-sil-verify-all %s -sil-combine -verify-skip-unreachable-must-be-last | %FileCheck %s
+// RUN: %target-sil-opt -enable-objc-interop -enforce-exclusivity=none -enable-sil-verify-all %s -sil-combine | %FileCheck %s
 
 // Declare this SIL to be canonical because some tests break raw SIL
 // conventions. e.g. address-type block args. -enforce-exclusivity=none is also

test/SILOptimizer/sil_combine_apply.sil

@@ -1,4 +1,4 @@
-// RUN: %target-sil-opt -enable-sil-verify-all %s -sil-combine -verify-skip-unreachable-must-be-last -sil-combine-disable-alloc-stack-opts | %FileCheck %s
+// RUN: %target-sil-opt -enable-sil-verify-all %s -sil-combine -sil-combine-disable-alloc-stack-opts | %FileCheck %s
 
 import Swift
 import Builtin

test/SILOptimizer/sil_combine_global_addr.sil

@@ -1,4 +1,4 @@
-// RUN: %target-sil-opt -enforce-exclusivity=none -enable-sil-verify-all %s -sil-combine -verify-skip-unreachable-must-be-last -devirtualizer | %FileCheck %s
+// RUN: %target-sil-opt -enforce-exclusivity=none -enable-sil-verify-all %s -sil-combine -devirtualizer | %FileCheck %s
 
 // Test to see if concrete type can be propagated from
 // global_addr in sil_combiner.

test/SILOptimizer/sil_combine_objc.sil

@@ -1,4 +1,4 @@
-// RUN: %target-sil-opt -enable-sil-verify-all %s -sil-combine -verify-skip-unreachable-must-be-last | %FileCheck %s
+// RUN: %target-sil-opt -enable-sil-verify-all %s -sil-combine | %FileCheck %s
 // REQUIRES: objc_interop
 
 // See https://bugs.swift.org/browse/SR-5065, rdar://32511494

utils/swift-autocomplete.bash

@@ -27,7 +27,6 @@ _swift_complete()
       -view-cfg-remove-use-list-comments \
       -view-cfg-only-for-function \
       -sil-print-no-color \
-      -verify-skip-unreachable-must-be-last \
       -aa \
       -cache-aa-results \
       -sil-dump-call-graph \