[flang] Handle missing substring upper bound better when folding

When folding a substring of a named constant or character literal, acquire the value of a missing upper bound from the base object. Differential Revision: https://reviews.llvm.org/D142942
llvm · Jan 31, 2023 · 8fed620 · 8fed620
1 parent bbddbe5
commit 8fed620
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Showing 3 changed files with 21 additions and 4 deletions.
diff --git a/flang/lib/Evaluate/variable.cpp b/flang/lib/Evaluate/variable.cpp
@@ -258,7 +258,20 @@ static std::optional<Expr<SubscriptInteger>> SymbolLEN(const Symbol &symbol) {
     }
   }
   if (auto dyType{DynamicType::From(ultimate)}) {
-    if (auto len{dyType->GetCharLength()}) {
+    auto len{dyType->GetCharLength()};
+    if (!len && ultimate.attrs().test(semantics::Attr::PARAMETER)) {
+      // Its initializer determines the length of an implied-length named
+      // constant.
+      if (const auto *object{
+              ultimate.detailsIf<semantics::ObjectEntityDetails>()}) {
+        if (object->init()) {
+          if (auto dyType2{DynamicType::From(*object->init())}) {
+            len = dyType2->GetCharLength();
+          }
+        }
+      }
+    }
+    if (len) {
       if (auto constLen{ToInt64(*len)}) {
         return Expr<SubscriptInteger>{std::max<std::int64_t>(*constLen, 0)};
       } else if (ultimate.owner().IsDerivedType() ||

diff --git a/flang/test/Evaluate/fold-substr.f90 b/flang/test/Evaluate/fold-substr.f90
@@ -14,4 +14,9 @@ module m
   logical, parameter :: test_05b = len(ca(:)(2:4)) == 3
   logical, parameter :: test_06a = ca(1)(1:2)//ca(2)(2:3)//ca(3)(3:4) == "abfgkl"
   logical, parameter :: test_06b = len(ca(1)(1:2)//ca(2)(2:3)//ca(3)(3:4)) == 6
+  logical, parameter :: test_07a = ca(1)(:2) == "ab"
+  logical, parameter :: test_07b = ca(1)(3:) == "cd"
+  logical, parameter :: test_07c = ca(1)(:-1) == ""
+  logical, parameter :: test_07d = ca(1)(5:) == ""
+  logical, parameter :: test_07e = ca(1)(:) == "abcd"
 end module
diff --git a/flang/test/Lower/character-local-variables.f90 b/flang/test/Lower/character-local-variables.f90
@@ -116,9 +116,8 @@ subroutine dyn_array_dyn_len_lb(l, n)
 subroutine assumed_length_param(n)
   character(*), parameter :: c(1)=(/"abcd"/)
   integer :: n
-  ! CHECK: %[[c4:.*]] = arith.constant 4 : index
-  ! CHECK: %[[len:.*]] = fir.convert %[[c4]] : (index) -> i64
-  ! CHECK: fir.store %[[len]] to %[[tmp:.*]] : !fir.ref<i64>
+  ! CHECK: %[[c4:.*]] = arith.constant 4 : i64
+  ! CHECK: fir.store %[[c4]] to %[[tmp:.*]] : !fir.ref<i64>
   ! CHECK: fir.call @_QPtake_int(%[[tmp]]) {{.*}}: (!fir.ref<i64>) -> ()
   call take_int(len(c(n), kind=8))
 end