Add SILBuilder constructors that take a DebugScope.

Allow a new SILBuilder to be created for an insertion point, while
providing all of its necessary context.

Ultimately, the builder's constructor should take an insertion point,
DebugLocation, and context. Then we won't need to pass SILLocation to
all of its methods.

This makes much more sense and is much safer than saving the insertion
point via an RAII object or defining a separate
SILBuilderWithScope. Those broken abstractions should go away.

Author: atrick

include/swift/SIL/SILBuilder.h

@@ -173,11 +173,20 @@ class SILBuilder {
   /// location.
   ///
   /// Clients should prefer this constructor.
-  SILBuilder(SILInstruction *I, SILBuilderContext &C)
+  SILBuilder(SILInstruction *I, const SILDebugScope *DS, SILBuilderContext &C)
       : TempContext(C.getModule()), C(C), F(I->getFunction()) {
+    assert(DS && "instruction has no debug scope");
+    setCurrentDebugScope(DS);
     setInsertionPoint(I);
   }
 
+  SILBuilder(SILBasicBlock *BB, const SILDebugScope *DS, SILBuilderContext &C)
+      : TempContext(C.getModule()), C(C), F(BB->getParent()) {
+    assert(DS && "block has no debug scope");
+    setCurrentDebugScope(DS);
+    setInsertionPoint(BB);
+  }
+
   // Allow a pass to override the current SIL module conventions. This should
   // only be done by a pass responsible for lowering SIL to a new stage
   // (e.g. AddressLowering).
@@ -2123,10 +2132,8 @@ class SILBuilderWithScope : public SILBuilder {
   ///
   /// Clients should prefer this constructor.
   SILBuilderWithScope(SILInstruction *I, SILBuilderContext &C)
-    : SILBuilder(I, C) {
-    assert(I->getDebugScope() && "instruction has no debug scope");
-    setCurrentDebugScope(I->getDebugScope());
-  }
+    : SILBuilder(I, I->getDebugScope(), C)
+  {}
 
   explicit SILBuilderWithScope(
       SILInstruction *I,