[capture-promotion] Add support for GEPs from captures that are load_borrowed.

We supported this code pattern previously just for loads and never implemented
the support for load_borrow. I just added analogous code for
load_borrow. Without this, we hit a crash since:

1. We would not process the struct_element_addr for a valid value.
2. The load_borrow would not look through the struct_element_addr, so we would
ask the cloner for the mapped value to the struct_element_addr... it was never
visited, thus never mapped, thus KABOOM.

rdar://93879907
(cherry picked from commit 3b39af3)

Author: gottesmm

lib/SILOptimizer/Mandatory/CapturePromotion.cpp

@@ -697,6 +697,25 @@ void ClosureCloner::visitLoadBorrowInst(LoadBorrowInst *lbi) {
     return;
   }
 
+  auto *seai = dyn_cast<StructElementAddrInst>(lbi->getOperand());
+  if (!seai) {
+    SILCloner<ClosureCloner>::visitLoadBorrowInst(lbi);
+    return;
+  }
+
+  if (SILValue value = getProjectBoxMappedVal(seai->getOperand())) {
+    // Loads of a struct_element_addr of an argument get replaced with a
+    // struct_extract of the new passed in value. The value should be borrowed
+    // already, so we can just extract the value.
+    assert(
+        !getBuilder().getFunction().hasOwnership() ||
+        value.getOwnershipKind().isCompatibleWith(OwnershipKind::Guaranteed));
+    value = getBuilder().emitStructExtract(lbi->getLoc(), value,
+                                           seai->getField(), lbi->getType());
+    recordFoldedValue(lbi, value);
+    return;
+  }
+
   SILCloner<ClosureCloner>::visitLoadBorrowInst(lbi);
   return;
 }

test/SILOptimizer/capture_promotion_ownership.sil

@@ -431,11 +431,15 @@ bb0:
 // CHECK:   [[BORROWED_BAZ:%.*]] = begin_borrow [[BAZ]] : $Baz
 // CHECK:   [[X:%.*]] = struct_extract [[BORROWED_BAZ]] : $Baz, #Baz.x
 // CHECK:   [[BAR:%.*]] = struct_extract [[BORROWED_BAZ]] : $Baz, #Baz.bar
+
 // CHECK:   [[BAR_COPY:%.*]] = copy_value [[BAR]]
+// CHECK:   [[BAR_COPY_2:%.*]] = copy_value [[BAR_COPY]]
 // CHECK:   [[BAR2:%.*]] = struct_extract [[BORROWED_BAZ]] : $Baz, #Baz.bar
 // CHECK:   [[BAR2_COPY:%.*]] = copy_value [[BAR2]]
 // CHECK:   [[BAR2_COPY_BORROW:%.*]] = begin_borrow [[BAR2_COPY]]
+// CHECK:   [[LOAD_BORROW_EXT:%.*]] = struct_extract [[BORROWED_BAZ]]
 // CHECK:   apply {{%.*}}([[BAR_COPY]], [[BAR2_COPY_BORROW]], [[X]])
+// CHECK:   apply {{%.*}}([[BAR_COPY_2]], [[LOAD_BORROW_EXT]], [[X]])
 // CHECK:   end_borrow [[BAR2_COPY_BORROW]]
 // CHECK:   destroy_value [[BAR2_COPY]]
 // CHECK:   end_borrow [[BORROWED_BAZ]]
@@ -458,12 +462,17 @@ bb0(%0 : @owned $<τ_0_0> { var τ_0_0 } <Baz>, %1 : @owned $<τ_0_0> { var τ_0
   %1a = project_box %1 : $<τ_0_0> { var τ_0_0 } <Baz>, 0
   %9 = struct_element_addr %1a : $*Baz, #Baz.x
   %10 = struct_element_addr %1a : $*Baz, #Baz.bar
+  %10a = struct_element_addr %1a : $*Baz, #Baz.bar
   %11 = load [trivial] %9 : $*Int
   %12 = load [copy] %10 : $*Bar
+  %12a = copy_value %12 : $Bar
   %13 = load [copy] %10 : $*Bar
   %14 = begin_borrow %13 : $Bar
   %15 = function_ref @destructured_baz_user : $@convention(thin) (@owned Bar, @guaranteed Bar, Int) -> ()
+  %16 = load_borrow %10a : $*Bar
   apply %15(%12, %14, %11) : $@convention(thin) (@owned Bar, @guaranteed Bar, Int) -> ()
+  apply %15(%12a, %16, %11) : $@convention(thin) (@owned Bar, @guaranteed Bar, Int) -> ()
+  end_borrow %16 : $Bar
   end_borrow %14 : $Bar
   destroy_value %13 : $Bar