[flang] Set LBOUND() folding for (x) expression as ones

[FruitClover]

Summary

Set LBOUND() constant folding for parentheses expr. as ones

Array bounds should not propagate throught omitted bounds specifications or
temporary variables - fix constant folding in case of Parentheses<T> expression
by explicitly returning array of ones (or scalar in case of DIM=).

Add set of tests for (x) bounds checks (w/ and w/o 'parameter' arrays)

[FruitClover]

Sync with base

[FruitClover]

Upd commit message

[jeanPerier]

LGTM

[FruitClover]

Rebase

flang/lib/Evaluate/fold-integer.cpp

template <typename T> ConstantSubscripts GetLbound(const Constant<T> &x) {
     if (dim_) {
       return {x.lbounds().at(*dim_)};
     } else {
       return x.lbounds();
     }
   }
 
   template <typename T> ConstantSubscripts GetLbound(const Parentheses<T> &x) {
-    // Strip off the parentheses
-    return GetLbound(x.left());
+    // LBOUND for (x) is [1, ..., 1] cause of temp variable inside
+    // parentheses (lower bound is omitted, the default value is 1).
+    return ConstantSubscripts(x.Rank(), ConstantSubscript{1});
   }
 
   template <typename T> ConstantSubscripts GetLbound(const Expr<T> &x) {
     // recurse through Expr<T>'a until we hit a constant
     return common::visit([&](const auto &inner) { return GetLbound(inner); },
         //      [&](const auto &) { return 0; },
         x.u);
   }

flang/test/Evaluate/folding08.f90

subroutine test3_lbound_parameter
     integer, parameter :: a3(-10:-5,1,4:6) = 0
     integer, parameter :: lba3(*) = lbound(a3)
     logical, parameter :: test_lba3 = all(lba3 == [-10, 1, 4])
     ! Exercise with DIM=
     logical, parameter :: test_lba3_dim = lbound(a3, 1) == -10 .and. &
          lbound(a3, 2) == 1 .and. &
          lbound(a3, 3) == 4
   end subroutine
+  subroutine test4_lbound_parentheses
+    ! Test lbound with (x) expressions
+    integer :: a1(1) = 0
+    logical, parameter :: test_lba1 = all(lbound((a1)) == [1])
+    integer :: a2(0:2) = 0
+    logical, parameter :: test_lba2 = all(lbound((a2)) == [1])
+    integer :: a3(-1:0) = 0
+    logical, parameter :: test_lba3 = all(lbound((a3)) == [1])
+    integer :: a4(-5:-1, 2:5) = 0
+    logical, parameter :: test_lba4 = all(lbound((a4)) == [1, 1])
+
+    ! Exercise with DIM=
+    logical, parameter :: test_lba4_dim = lbound((a4), 1) == 1 .and. &
+         lbound((a4), 2) == 1
+
+    ! Exercise with parameter types
+    integer, parameter :: pa1(1) = 0
+    logical, parameter :: test_lbpa1 = all(lbound((pa1)) == [1])
+    integer, parameter :: pa2(0:2) = 0
+    logical, parameter :: test_lbpa2 = all(lbound((pa2)) == [1])
+    integer, parameter :: pa3(-1:0) = 0
+    logical, parameter :: test_lbpa3 = all(lbound((pa3)) == [1])
+    integer, parameter :: pa4(-5:-1, 2:5) = 0
+    logical, parameter :: test_lbpa4 = all(lbound((pa4)) == [1, 1])
+
+    ! Exercise with DIM=
+    logical, parameter :: test_lbpa4_dim = lbound((pa4), 1) == 1 .and. &
+         lbound((pa4), 2) == 1
+  end
 end

flang/test/Evaluate/folding16.f90

 ! RUN: %python %S/test_folding.py %s %flang_fc1
 ! Ensure that lower bounds are accounted for in intrinsic folding;
 ! this is a regression test for a bug in which they were not
 module m
   real, parameter :: a(-1:-1) = 1.
   real, parameter :: b(-1:-1) = log(a)
   integer, parameter :: c(-1:1) = [33, 22, 11]
   integer, parameter :: d(1:3) = [33, 22, 11]
   integer, parameter :: e(-2:0) = ([33, 22, 11])
-  logical, parameter :: test_1 = lbound((a),1)==-1 .and. lbound(b,1)==-1 .and. &
+  logical, parameter :: test_1 = lbound((a),1)==1 .and. lbound(b,1)==-1 .and. &
                                lbound(log(a),1)==1 .and. all(b==0)
   logical, parameter :: test_2 = all(c .eq. d)
   logical, parameter :: test_3 = all(c .eq. e)
   logical, parameter :: test_4 = all(d .eq. e)
 end