[flang][runtime] Fix namelist substring checking

[klausler]

An || operator in namelist substring bounds checking really needs to be an && operator so that the substring is viewed as correct only when both its bounds are valid.

Fixes llvm-test-suite/Fortran/gfortran/regression/namelist_40.f90.

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Author: Peter Klausler (klausler)

Changes

An || operator in namelist substring bounds checking really needs to be an && operator so that the substring is viewed as correct only when both its bounds are valid.

Fixes llvm-test-suite/Fortran/gfortran/regression/namelist_40.f90.

---

Full diff: https://github.com/llvm/llvm-project/pull/78649.diff

1 Files Affected:

• (modified) flang/runtime/namelist.cpp (+1-1)

diff --git a/flang/runtime/namelist.cpp b/flang/runtime/namelist.cpp
index 848ebcf300a3d9..f5d7404fdcb86b 100644
--- a/flang/runtime/namelist.cpp
+++ b/flang/runtime/namelist.cpp
@@ -313,7 +313,7 @@ static bool HandleSubstring(
         desc.raw().elem_len = 0;
         return true;
       }
-      if (*lower >= 1 || *upper <= chars) {
+      if (*lower >= 1 && *upper <= chars) {
         // Offset the base address & adjust the element byte length
         desc.raw().elem_len = (*upper - *lower + 1) * kind;
         desc.set_base_addr(reinterpret_cast<void *>(