Handle undefs in a few utilities used in RLE (#59448)

Author: meg-gupta

include/swift/SILOptimizer/Utils/LoadStoreOptUtils.h

@@ -257,6 +257,8 @@ class LSValue : public LSBase {
   SILValue materialize(SILInstruction *Inst) {
     if (CoveringValue)
       return SILValue();
+    if (isa<SILUndef>(Base))
+      return Base;
     auto Val = Base;
     auto InsertPt = getInsertAfterPoint(Base).getValue();
     SILBuilderWithScope Builder(InsertPt);

lib/SILOptimizer/Utils/InstOptUtils.cpp

@@ -1683,6 +1683,9 @@ SILBasicBlock::iterator swift::replaceSingleUse(Operand *use, SILValue newValue,
 }
 
 SILValue swift::makeCopiedValueAvailable(SILValue value, SILBasicBlock *inBlock) {
+  if (isa<SILUndef>(value))
+    return value;
+
   if (!value->getFunction()->hasOwnership())
     return value;
 
@@ -1698,6 +1701,9 @@ SILValue swift::makeCopiedValueAvailable(SILValue value, SILBasicBlock *inBlock)
 }
 
 SILValue swift::makeValueAvailable(SILValue value, SILBasicBlock *inBlock) {
+  if (isa<SILUndef>(value))
+    return value;
+
   if (!value->getFunction()->hasOwnership())
     return value;
 

test/SILOptimizer/redundant_load_elim.sil

@@ -1270,3 +1270,22 @@ bb0:
   dealloc_stack_ref %1 : $AX
   return %5 : $Int32
 }
+
+sil @read_emptytuple : $@convention(thin) (@in_guaranteed ()) -> ()
+
+// CHECK-LABEL: sil @emptytuple_promotion :
+// CHECK: store
+// CHECK-LABEL: } // end sil function 'emptytuple_promotion'
+sil @emptytuple_promotion : $@convention(thin) () -> () {
+bb0:
+  %stk2 = alloc_stack $()
+  store undef to %stk2 : $*()
+  br bb1
+
+bb1:
+  %ld = load %stk2 : $*()
+  dealloc_stack %stk2 : $*()
+  %r = tuple ()
+  return %r : $()
+}
+