Generalize and fix SinkAddressProjections.

Fixes a potential real bug in the case that SinkAddressProjections moves
projections without notifying SimplifyCFG of the change. This could
fail to update Analyses (probably won't break anything in practice).

Introduce SILInstruction::isPure. Among other things, this can tell
you if it's safe to duplicate instructions at their
uses. SinkAddressProjections should check this before sinking uses. I
couldn't find a way to expose this as a real bug, but it is a
theoretical bug.

Add the SinkAddressProjections functionality to the BasicBlockCloner
utility. Enable address projection sinking for all BasicBlockCloner
clients (the four different kinds of jump-threading that use it). This
brings the compiler much closer to banning all address phis.

The "bugs" were originally introduced a week ago here:

commit f22371bf0b (fork/fix-address-phi, fix-address-phi)
Author: Andrew Trick <atrick@apple.com>
Date:   Tue Sep 17 16:45:51 2019

    Add SIL SinkAddressProjections utility to avoid address phis.

    Enable this utility during jump-threading in SimplifyCFG.

    Ultimately, the SIL verifier should prevent all address-phis and we'll
    need to use this utility in a few more places.

    Fixes <rdar://problem/55320867> SIL verification failed: Unknown
    formal access pattern: storage

test/DebugInfo/inlined-generics-basic.swift

@@ -43,8 +43,8 @@ public class C<R> {
   let r : R
   init(_ _r: R) { r = _r }
 
-  // SIL: // C.f<A>(_:)
-  // IR: define {{.*}} @"$s1A1CC1fyyqd__lF"
+  // SIL-LABEL: // C.f<A>(_:)
+  // IR-LABEL: define {{.*}} @"$s1A1CC1fyyqd__lF"
 #sourceLocation(file: "f.swift", line: 1)
   public func f<S>(_ s: S) {
     // SIL: debug_value_addr %0 : $*S, let, name "s", argno 1,{{.*}} scope [[F]]
@@ -57,7 +57,13 @@ public class C<R> {
     // IR: call {{.*}}3use
 #sourceLocation(file: "f.swift", line: 2)
     g(s)
-    // IR: dbg.value({{.*}}, metadata ![[GR_T:[0-9]+]]
+    // Jump-threading removes the basic block containing debug_value
+    // "t" before the second call to `g(r)`. When this happens, the
+    // ref_element_addr in that removed block is left with a single
+    // debug_value use, so they are both deleted. This means we have
+    // no debug value for "t" in the call to `g(r)`.
+    //   dbg.value({{.*}}, metadata ![[GR_T:[0-9]+]]
+
     // IR: dbg.value({{.*}}, metadata ![[GR_U:[0-9]+]]
     // IR: call {{.*}}3use
 #sourceLocation(file: "f.swift", line: 3)
@@ -81,6 +87,8 @@ public class C<R> {
     g(false)
   }
 }
+// SIL-LABEL: } // end sil function '$s1A1CC1fyyqd__lF'
+// IR-LABEL: ret void
 
 // IR: ![[BOOL:[0-9]+]] = !DICompositeType({{.*}}name: "Bool"
 // IR: ![[LET_BOOL:[0-9]+]] = !DIDerivedType(tag: DW_TAG_const_type, baseType: ![[BOOL]])
@@ -96,9 +104,12 @@ public class C<R> {
 // IR: ![[SP_GS_T]] = {{.*}}linkageName: "$s1A1gyyxlFqd___Ti5"
 // IR: ![[GS_U]] = !DILocalVariable(name: "u", {{.*}} scope: ![[SP_GS_U:[0-9]+]], {{.*}} type: ![[LET_TAU_1_0]])
 // IR: ![[SP_GS_U]] = {{.*}}linkageName: "$s1A1hyyxlFqd___Ti5"
-// IR: ![[GR_T]] = !DILocalVariable(name: "t", {{.*}} scope: ![[SP_GR_T:[0-9]+]], {{.*}}type: ![[LET_TAU_0_0]])
+
+// Debug info for this variable is removed. See the note above the call to g(r).
+//   ![[GR_T]] = !DILocalVariable(name: "t", {{.*}} scope: ![[SP_GR_T:[0-9]+]], {{.*}}type: ![[LET_TAU_0_0]])
 // S has the same generic parameter numbering s T and U.
-// IR: ![[SP_GR_T]] = {{.*}}linkageName: "$s1A1gyyxlF"
+//   ![[SP_GR_T]] = {{.*}}linkageName: "$s1A1gyyxlF"
+
 // IR: ![[GR_U]] = !DILocalVariable(name: "u", {{.*}} scope: ![[SP_GR_U:[0-9]+]], {{.*}}type: ![[LET_TAU_0_0]])
 // IR: ![[SP_GR_U]] = {{.*}}linkageName: "$s1A1hyyxlF"
 // IR: ![[GRS_T]] = !DILocalVariable(name: "t", {{.*}} scope: ![[SP_GRS_T:[0-9]+]], {{.*}}type: ![[LET_TUPLE:[0-9]+]]