[SIL] Let addArgumentToBranch accept plural args.

Previously, the addArgumentToBranch only allowed one to add a single
additional argument to a branch.  It then verified the argument count.
That is a problem if multiple arguments have to be added to arrive at
the correct argument count.

Specifically, that was a problem when running Mem2Reg on a lexical
alloc_stack, where three new phi arguments are added.

Here, the function name is changed to addArgumentsToBranch (plural
arguments) and the function accepts a SmallVector<SILValue> rather than
a single SILValue, allowing one to add all the arguments that are
necessary in order to verify that the resulting number of arguments is
correct.

Author: nate-chandler

include/swift/SILOptimizer/Utils/InstOptUtils.h

@@ -190,11 +190,11 @@ bool isAddressOfArrayElement(SILValue addr);
 /// Move an ApplyInst's FuncRef so that it dominates the call site.
 void placeFuncRef(ApplyInst *ai, DominanceInfo *dt);
 
-/// Add an argument, \p val, to the branch-edge that is pointing into
+/// Add arguments, \p vals, to the branch-edge that is pointing into
 /// block \p Dest. Return a new instruction and do not erase the old
 /// instruction.
-TermInst *addArgumentToBranch(SILValue val, SILBasicBlock *dest,
-                              TermInst *branch);
+TermInst *addArgumentsToBranch(ArrayRef<SILValue> vals, SILBasicBlock *dest,
+                               TermInst *branch);
 
 /// Get the linkage to be used for specializations of a function with
 /// the given linkage.

lib/SILOptimizer/Utils/InstOptUtils.cpp

@@ -864,8 +864,8 @@ void swift::placeFuncRef(ApplyInst *ai, DominanceInfo *domInfo) {
 /// Add an argument, \p val, to the branch-edge that is pointing into
 /// block \p Dest. Return a new instruction and do not erase the old
 /// instruction.
-TermInst *swift::addArgumentToBranch(SILValue val, SILBasicBlock *dest,
-                                     TermInst *branch) {
+TermInst *swift::addArgumentsToBranch(ArrayRef<SILValue> vals,
+                                      SILBasicBlock *dest, TermInst *branch) {
   SILBuilderWithScope builder(branch);
 
   if (auto *cbi = dyn_cast<CondBranchInst>(branch)) {
@@ -879,10 +879,12 @@ TermInst *swift::addArgumentToBranch(SILValue val, SILBasicBlock *dest,
       falseArgs.push_back(arg);
 
     if (dest == cbi->getTrueBB()) {
-      trueArgs.push_back(val);
+      for (auto val : vals)
+        trueArgs.push_back(val);
       assert(trueArgs.size() == dest->getNumArguments());
     } else {
-      falseArgs.push_back(val);
+      for (auto val : vals)
+        falseArgs.push_back(val);
       assert(falseArgs.size() == dest->getNumArguments());
     }
 
@@ -898,7 +900,8 @@ TermInst *swift::addArgumentToBranch(SILValue val, SILBasicBlock *dest,
     for (auto arg : bi->getArgs())
       args.push_back(arg);
 
-    args.push_back(val);
+    for (auto val : vals)
+      args.push_back(val);
     assert(args.size() == dest->getNumArguments());
     return builder.createBranch(bi->getLoc(), bi->getDestBB(), args);
   }