Lower length expr to max(expr, 0) - cover dummy case

#1276 missed
the case where the character with explicit length is a dummy argument.

Cover this here and update more tests.

Author: jeanPerier

flang/include/flang/Lower/ConvertExpr.h

@@ -210,6 +210,10 @@ inline mlir::NamedAttribute getAdaptToByRefAttr(fir::FirOpBuilder &builder) {
           builder.getUnitAttr()};
 }
 
+/// Generate max(\p value, 0) where \p value is a scalar integer.
+mlir::Value genMaxWithZero(fir::FirOpBuilder &builder, mlir::Location loc,
+                           mlir::Value value);
+
 } // namespace Fortran::lower
 
 #endif // FORTRAN_LOWER_CONVERTEXPR_H

flang/lib/Lower/ConvertExpr.cpp

@@ -1755,6 +1755,8 @@ class ScalarExprLowering {
           if (const Fortran::semantics::MaybeIntExpr &lenExpr =
                   type->characterTypeSpec().length().GetExplicit()) {
             mlir::Value len = fir::getBase(genval(*lenExpr));
+            // F2018 7.4.4.2 point 5.
+            len = Fortran::lower::genMaxWithZero(builder, getLoc(), len);
             symMap.addSymbol(*arg,
                              replaceScalarCharacterLength(gen(*expr), len));
             continue;
@@ -6298,3 +6300,15 @@ void Fortran::lower::createArrayMergeStores(
   esp.resetBindings();
   esp.incrementCounter();
 }
+
+mlir::Value Fortran::lower::genMaxWithZero(fir::FirOpBuilder &builder,
+                                           mlir::Location loc,
+                                           mlir::Value value) {
+  mlir::Value zero = builder.createIntegerConstant(loc, value.getType(), 0);
+  if (auto definingOp = value.getDefiningOp())
+    if (auto cst = mlir::dyn_cast<mlir::arith::ConstantOp>(definingOp))
+      if (auto intAttr = cst.value().dyn_cast<mlir::IntegerAttr>())
+        return intAttr.getInt() < 0 ? zero : value;
+  return Fortran::lower::genMax(builder, loc,
+                                llvm::SmallVector<mlir::Value>{value, zero});
+}

flang/lib/Lower/ConvertVariable.cpp

@@ -1248,9 +1248,7 @@ void Fortran::lower::mapSymbolAttributes(
     auto rawLen = genValue(*charLen);
     // If the length expression is negative, the length is zero. See
     // F2018 7.4.4.2 point 5.
-    auto zero = builder.createIntegerConstant(loc, rawLen.getType(), 0);
-    return Fortran::lower::genMax(builder, loc,
-                                  llvm::SmallVector<mlir::Value>{rawLen, zero});
+    return genMaxWithZero(builder, loc, rawLen);
   };
 
   ba.match(
@@ -1329,7 +1327,7 @@ void Fortran::lower::mapSymbolAttributes(
           }
           // Override LEN with an expression
           if (charLen)
-            len = genValue(*charLen);
+            len = genExplicitCharLen(charLen);
           symMap.addCharSymbol(sym, boxAddr, len, true);
           return;
         }
@@ -1491,15 +1489,15 @@ void Fortran::lower::mapSymbolAttributes(
           addr = unboxchar.first;
           if (charLen) {
             // Set/override LEN with an expression
-            len = genValue(*charLen);
+            len = genExplicitCharLen(charLen);
           } else {
             // LEN is from the boxchar
             len = unboxchar.second;
             mustBeDummy = true;
           }
         } else {
           // local CHARACTER variable
-          len = genExplicitCharLen(*charLen);
+          len = genExplicitCharLen(charLen);
         }
         llvm::SmallVector<mlir::Value> lengths = {len};
 
@@ -1617,7 +1615,7 @@ void Fortran::lower::mapSymbolAttributes(
             addr = builder.create<fir::BoxAddrOp>(loc, refTy, argBox);
             if (charLen)
               // Set/override LEN with an expression.
-              len = genValue(*charLen);
+              len = genExplicitCharLen(charLen);
             else
               // Get the length from the actual arguments.
               len = charHelp.readLengthFromBox(argBox);
@@ -1626,15 +1624,15 @@ void Fortran::lower::mapSymbolAttributes(
             addr = unboxchar.first;
             if (charLen) {
               // Set/override LEN with an expression
-              len = genValue(*charLen);
+              len = genExplicitCharLen(charLen);
             } else {
               // Get the length from the actual arguments.
               len = unboxchar.second;
             }
           }
         } else {
           // local CHARACTER variable
-          len = genExplicitCharLen(*charLen);
+          len = genExplicitCharLen(charLen);
         }
         llvm::SmallVector<mlir::Value> lengths = {len};