[flang-commits] [flang] [flang] Add hlfir.char_trim operation (PR #156064)

Leandro Lupori via flang-commits flang-commits at lists.llvm.org
Wed Sep 3 09:59:36 PDT 2025


https://github.com/luporl updated https://github.com/llvm/llvm-project/pull/156064

>From e9756e693d54c006ea7682b7762b541dbe7bf29d Mon Sep 17 00:00:00 2001
From: Leandro Lupori <leandro.lupori at linaro.org>
Date: Thu, 28 Aug 2025 15:03:23 -0300
Subject: [PATCH 1/2] [flang] Add hlfir.char_trim operation

Fortran character trim is currently lowered directly into a runtime
call, which makes it more complex to simplify expressions using it.

With this patch trim is first lowered into an hlfir.char_trim
operation, that is only later transformed into a runtime call.
This makes it easier to remove unnecessary calls to trim, as
proposed in #154593.
---
 .../include/flang/Optimizer/HLFIR/HLFIROps.td |  17 +++
 flang/lib/Lower/HlfirIntrinsics.cpp           |  24 ++++
 flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp     |  26 ++++
 .../HLFIR/Transforms/LowerHLFIRIntrinsics.cpp |  44 +++++--
 flang/test/HLFIR/trim.fir                     |  42 +++++++
 flang/test/Lower/HLFIR/trim.f90               |  22 ++++
 flang/test/Lower/volatile-string.f90          | 111 ++++++++----------
 7 files changed, 217 insertions(+), 69 deletions(-)
 create mode 100644 flang/test/HLFIR/trim.fir
 create mode 100644 flang/test/Lower/HLFIR/trim.f90

diff --git a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
index f58dde589aaf5..4b990a1c94c72 100644
--- a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
+++ b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
@@ -368,6 +368,23 @@ def hlfir_CmpCharOp : hlfir_Op<"cmpchar",
   let hasVerifier = 1;
 }
 
+def hlfir_CharTrimOp
+    : hlfir_Op<
+          "char_trim", [DeclareOpInterfaceMethods<MemoryEffectsOpInterface>]> {
+  let summary = "trim character";
+  let description = [{ Trim a character string. }];
+
+  let arguments = (ins AnyScalarCharacterEntity:$chr);
+
+  let results = (outs AnyScalarCharacterExpr);
+
+  let assemblyFormat = [{
+      $chr attr-dict `:` functional-type(operands, results)
+  }];
+
+  let builders = [OpBuilder<(ins "mlir::Value":$chr)>];
+}
+
 def hlfir_AllOp : hlfir_Op<"all", [DeclareOpInterfaceMethods<MemoryEffectsOpInterface>]> {
   let summary = "ALL transformational intrinsic";
   let description = [{
diff --git a/flang/lib/Lower/HlfirIntrinsics.cpp b/flang/lib/Lower/HlfirIntrinsics.cpp
index 39595d6f519ad..b9731e993db8f 100644
--- a/flang/lib/Lower/HlfirIntrinsics.cpp
+++ b/flang/lib/Lower/HlfirIntrinsics.cpp
@@ -159,6 +159,18 @@ class HlfirCharExtremumLowering : public HlfirTransformationalIntrinsic {
   hlfir::CharExtremumPredicate pred;
 };
 
+class HlfirCharTrimLowering : public HlfirTransformationalIntrinsic {
+public:
+  HlfirCharTrimLowering(fir::FirOpBuilder &builder, mlir::Location loc)
+      : HlfirTransformationalIntrinsic(builder, loc) {}
+
+protected:
+  mlir::Value
+  lowerImpl(const Fortran::lower::PreparedActualArguments &loweredActuals,
+            const fir::IntrinsicArgumentLoweringRules *argLowering,
+            mlir::Type stmtResultType) override;
+};
+
 class HlfirCShiftLowering : public HlfirTransformationalIntrinsic {
 public:
   using HlfirTransformationalIntrinsic::HlfirTransformationalIntrinsic;
@@ -421,6 +433,15 @@ mlir::Value HlfirCharExtremumLowering::lowerImpl(
   return createOp<hlfir::CharExtremumOp>(pred, mlir::ValueRange{operands});
 }
 
+mlir::Value HlfirCharTrimLowering::lowerImpl(
+    const Fortran::lower::PreparedActualArguments &loweredActuals,
+    const fir::IntrinsicArgumentLoweringRules *argLowering,
+    mlir::Type stmtResultType) {
+  auto operands = getOperandVector(loweredActuals, argLowering);
+  assert(operands.size() == 1);
+  return createOp<hlfir::CharTrimOp>(operands[0]);
+}
+
 mlir::Value HlfirCShiftLowering::lowerImpl(
     const Fortran::lower::PreparedActualArguments &loweredActuals,
     const fir::IntrinsicArgumentLoweringRules *argLowering,
@@ -555,6 +576,9 @@ std::optional<hlfir::EntityWithAttributes> Fortran::lower::lowerHlfirIntrinsic(
       return HlfirCharExtremumLowering{builder, loc,
                                        hlfir::CharExtremumPredicate::max}
           .lower(loweredActuals, argLowering, stmtResultType);
+    if (name == "trim")
+      return HlfirCharTrimLowering{builder, loc}.lower(
+          loweredActuals, argLowering, stmtResultType);
   }
   return std::nullopt;
 }
diff --git a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
index 964d183631186..6a2a28e3b6832 100644
--- a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
+++ b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
@@ -854,6 +854,32 @@ void hlfir::CmpCharOp::getEffects(
   getIntrinsicEffects(getOperation(), effects);
 }
 
+//===----------------------------------------------------------------------===//
+// CharTrimOp
+//===----------------------------------------------------------------------===//
+
+void hlfir::CharTrimOp::build(mlir::OpBuilder &builder,
+                              mlir::OperationState &result, mlir::Value chr) {
+  fir::CharacterType::LenType len;
+  if (auto cstLen = getCharacterLengthIfStatic(chr.getType()))
+    len = *cstLen;
+  else
+    len = fir::CharacterType::unknownLen();
+  unsigned kind = getCharacterKind(chr.getType());
+  auto resultType = hlfir::ExprType::get(
+      builder.getContext(), hlfir::ExprType::Shape{},
+      fir::CharacterType::get(builder.getContext(), kind, len),
+      /*polymorphic=*/false);
+  build(builder, result, resultType, chr);
+}
+
+void hlfir::CharTrimOp::getEffects(
+    llvm::SmallVectorImpl<
+        mlir::SideEffects::EffectInstance<mlir::MemoryEffects::Effect>>
+        &effects) {
+  getIntrinsicEffects(getOperation(), effects);
+}
+
 //===----------------------------------------------------------------------===//
 // NumericalReductionOp
 //===----------------------------------------------------------------------===//
diff --git a/flang/lib/Optimizer/HLFIR/Transforms/LowerHLFIRIntrinsics.cpp b/flang/lib/Optimizer/HLFIR/Transforms/LowerHLFIRIntrinsics.cpp
index 8b6c7decb2a0a..a913cfadcefc2 100644
--- a/flang/lib/Optimizer/HLFIR/Transforms/LowerHLFIRIntrinsics.cpp
+++ b/flang/lib/Optimizer/HLFIR/Transforms/LowerHLFIRIntrinsics.cpp
@@ -585,6 +585,34 @@ class CmpCharOpConversion : public HlfirIntrinsicConversion<hlfir::CmpCharOp> {
   }
 };
 
+class CharTrimOpConversion
+    : public HlfirIntrinsicConversion<hlfir::CharTrimOp> {
+  using HlfirIntrinsicConversion<hlfir::CharTrimOp>::HlfirIntrinsicConversion;
+
+  llvm::LogicalResult
+  matchAndRewrite(hlfir::CharTrimOp trim,
+                  mlir::PatternRewriter &rewriter) const override {
+    fir::FirOpBuilder builder{rewriter, trim.getOperation()};
+    const mlir::Location &loc = trim->getLoc();
+
+    llvm::SmallVector<IntrinsicArgument, 1> inArgs;
+    mlir::Value chr = trim.getChr();
+    inArgs.push_back({chr, chr.getType()});
+
+    auto *argLowering = fir::getIntrinsicArgumentLowering("trim");
+    llvm::SmallVector<fir::ExtendedValue, 1> args =
+        lowerArguments(trim, inArgs, rewriter, argLowering);
+
+    mlir::Type resultType = hlfir::getFortranElementType(trim.getType());
+
+    auto [resultExv, mustBeFreed] =
+        fir::genIntrinsicCall(builder, loc, "trim", resultType, args);
+
+    processReturnValue(trim, resultExv, mustBeFreed, builder, rewriter);
+    return mlir::success();
+  }
+};
+
 class LowerHLFIRIntrinsics
     : public hlfir::impl::LowerHLFIRIntrinsicsBase<LowerHLFIRIntrinsics> {
 public:
@@ -592,14 +620,14 @@ class LowerHLFIRIntrinsics
     mlir::ModuleOp module = this->getOperation();
     mlir::MLIRContext *context = &getContext();
     mlir::RewritePatternSet patterns(context);
-    patterns.insert<MatmulOpConversion, MatmulTransposeOpConversion,
-                    AllOpConversion, AnyOpConversion, SumOpConversion,
-                    ProductOpConversion, TransposeOpConversion,
-                    CountOpConversion, DotProductOpConversion,
-                    MaxvalOpConversion, MinvalOpConversion, MinlocOpConversion,
-                    MaxlocOpConversion, ArrayShiftOpConversion<hlfir::CShiftOp>,
-                    ArrayShiftOpConversion<hlfir::EOShiftOp>,
-                    ReshapeOpConversion, CmpCharOpConversion>(context);
+    patterns.insert<
+        MatmulOpConversion, MatmulTransposeOpConversion, AllOpConversion,
+        AnyOpConversion, SumOpConversion, ProductOpConversion,
+        TransposeOpConversion, CountOpConversion, DotProductOpConversion,
+        MaxvalOpConversion, MinvalOpConversion, MinlocOpConversion,
+        MaxlocOpConversion, ArrayShiftOpConversion<hlfir::CShiftOp>,
+        ArrayShiftOpConversion<hlfir::EOShiftOp>, ReshapeOpConversion,
+        CmpCharOpConversion, CharTrimOpConversion>(context);
 
     // While conceptually this pass is performing dialect conversion, we use
     // pattern rewrites here instead of dialect conversion because this pass
diff --git a/flang/test/HLFIR/trim.fir b/flang/test/HLFIR/trim.fir
new file mode 100644
index 0000000000000..8cf4a6d1201bd
--- /dev/null
+++ b/flang/test/HLFIR/trim.fir
@@ -0,0 +1,42 @@
+// RUN: fir-opt --lower-hlfir-intrinsics %s | FileCheck %s
+
+// CHECK-LABEL:   func.func @_QPtrim_test(
+// CHECK-SAME:      %[[ARG0:.*]]: !fir.boxchar<1> {fir.bindc_name = "c"}) {
+// CHECK:           %[[VAL_0:.*]] = arith.constant true
+// CHECK:           %[[VAL_2:.*]] = arith.constant 0 : index
+// CHECK:           %[[VAL_3:.*]] = arith.constant 8 : index
+// CHECK:           %[[VAL_4:.*]] = fir.alloca !fir.box<!fir.heap<!fir.char<1,?>>>
+// CHECK:           %[[VAL_5:.*]] = fir.dummy_scope : !fir.dscope
+// CHECK:           %[[VAL_6:.*]]:2 = fir.unboxchar %[[ARG0]] : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+// CHECK:           %[[VAL_7:.*]]:2 = hlfir.declare %[[VAL_6]]#0 typeparams %[[VAL_6]]#1 dummy_scope %[[VAL_5]] {uniq_name = "_QFtrim_testEc"} : (!fir.ref<!fir.char<1,?>>, index, !fir.dscope) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+// CHECK:           %[[VAL_8:.*]] = fir.alloca !fir.char<1,8> {bindc_name = "tc", uniq_name = "_QFtrim_testEtc"}
+// CHECK:           %[[VAL_9:.*]]:2 = hlfir.declare %[[VAL_8]] typeparams %[[VAL_3]] {uniq_name = "_QFtrim_testEtc"} : (!fir.ref<!fir.char<1,8>>, index) -> (!fir.ref<!fir.char<1,8>>, !fir.ref<!fir.char<1,8>>)
+// CHECK:           %[[VAL_10:.*]] = fir.embox %[[VAL_7]]#1 typeparams %[[VAL_6]]#1 : (!fir.ref<!fir.char<1,?>>, index) -> !fir.box<!fir.char<1,?>>
+// CHECK:           %[[VAL_11:.*]] = fir.zero_bits !fir.heap<!fir.char<1,?>>
+// CHECK:           %[[VAL_12:.*]] = fir.embox %[[VAL_11]] typeparams %[[VAL_2]] : (!fir.heap<!fir.char<1,?>>, index) -> !fir.box<!fir.heap<!fir.char<1,?>>>
+// CHECK:           fir.store %[[VAL_12]] to %[[VAL_4]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,?>>>>
+// CHECK:           %[[VAL_14:.*]] = fir.convert %[[VAL_4]] : (!fir.ref<!fir.box<!fir.heap<!fir.char<1,?>>>>) -> !fir.ref<!fir.box<none>>
+// CHECK:           %[[VAL_15:.*]] = fir.convert %[[VAL_10]] : (!fir.box<!fir.char<1,?>>) -> !fir.box<none>
+// CHECK:           fir.call @_FortranATrim(%[[VAL_14]], %[[VAL_15]], %{{.*}}, %{{.*}}) : (!fir.ref<!fir.box<none>>, !fir.box<none>, !fir.ref<i8>, i32) -> ()
+// CHECK:           %[[VAL_17:.*]] = fir.load %[[VAL_4]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,?>>>>
+// CHECK:           %[[VAL_18:.*]] = fir.box_elesize %[[VAL_17]] : (!fir.box<!fir.heap<!fir.char<1,?>>>) -> index
+// CHECK:           %[[VAL_19:.*]] = fir.box_addr %[[VAL_17]] : (!fir.box<!fir.heap<!fir.char<1,?>>>) -> !fir.heap<!fir.char<1,?>>
+// CHECK:           %[[VAL_20:.*]]:2 = hlfir.declare %[[VAL_19]] typeparams %[[VAL_18]] {uniq_name = ".tmp.intrinsic_result"} : (!fir.heap<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.heap<!fir.char<1,?>>)
+// CHECK:           %[[VAL_21:.*]] = hlfir.as_expr %[[VAL_20]]#0 move %[[VAL_0]] : (!fir.boxchar<1>, i1) -> !hlfir.expr<!fir.char<1,?>>
+// CHECK:           hlfir.assign %[[VAL_21]] to %[[VAL_9]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.ref<!fir.char<1,8>>
+// CHECK:           hlfir.destroy %[[VAL_21]] : !hlfir.expr<!fir.char<1,?>>
+// CHECK:           return
+// CHECK:         }
+
+func.func @_QPtrim_test(%arg0: !fir.boxchar<1> {fir.bindc_name = "c"}) {
+  %0 = fir.dummy_scope : !fir.dscope
+  %1:2 = fir.unboxchar %arg0 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+  %2:2 = hlfir.declare %1#0 typeparams %1#1 dummy_scope %0 {uniq_name = "_QFtrim_testEc"} : (!fir.ref<!fir.char<1,?>>, index, !fir.dscope) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+  %c8 = arith.constant 8 : index
+  %3 = fir.alloca !fir.char<1,8> {bindc_name = "tc", uniq_name = "_QFtrim_testEtc"}
+  %4:2 = hlfir.declare %3 typeparams %c8 {uniq_name = "_QFtrim_testEtc"} : (!fir.ref<!fir.char<1,8>>, index) -> (!fir.ref<!fir.char<1,8>>, !fir.ref<!fir.char<1,8>>)
+  %5 = hlfir.char_trim %2#0 : (!fir.boxchar<1>) -> !hlfir.expr<!fir.char<1,?>>
+  hlfir.assign %5 to %4#0 : !hlfir.expr<!fir.char<1,?>>, !fir.ref<!fir.char<1,8>>
+  hlfir.destroy %5 : !hlfir.expr<!fir.char<1,?>>
+  return
+}
diff --git a/flang/test/Lower/HLFIR/trim.f90 b/flang/test/Lower/HLFIR/trim.f90
new file mode 100644
index 0000000000000..ea1bd4fadead2
--- /dev/null
+++ b/flang/test/Lower/HLFIR/trim.f90
@@ -0,0 +1,22 @@
+! RUN: %flang_fc1 -emit-hlfir %s -o - | FileCheck %s
+
+! CHECK-LABEL:  func.func @_QPtrim_test(
+! CHECK-SAME:     %[[VAL_0:.*]]: !fir.boxchar<1> {fir.bindc_name = "c"}) {
+! CHECK:          %[[VAL_1:.*]] = fir.dummy_scope : !fir.dscope
+! CHECK-NEXT:     %[[VAL_2:.*]]:2 = fir.unboxchar %[[VAL_0]] : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK-NEXT:     %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_2]]#0 typeparams %[[VAL_2]]#1 dummy_scope %[[VAL_1]] {uniq_name = "_QFtrim_testEc"} : (!fir.ref<!fir.char<1,?>>, index, !fir.dscope) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK-NEXT:     %[[VAL_4:.*]] = arith.constant 8 : index
+! CHECK-NEXT:     %[[VAL_5:.*]] = fir.alloca !fir.char<1,8> {bindc_name = "tc", uniq_name = "_QFtrim_testEtc"}
+! CHECK-NEXT:     %[[VAL_6:.*]]:2 = hlfir.declare %[[VAL_5]] typeparams %[[VAL_4]] {uniq_name = "_QFtrim_testEtc"} : (!fir.ref<!fir.char<1,8>>, index) -> (!fir.ref<!fir.char<1,8>>, !fir.ref<!fir.char<1,8>>)
+! CHECK-NEXT:     %[[VAL_7:.*]] = hlfir.char_trim %[[VAL_3]]#0 : (!fir.boxchar<1>) -> !hlfir.expr<!fir.char<1,?>>
+! CHECK-NEXT:     hlfir.assign %[[VAL_7]] to %[[VAL_6]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.ref<!fir.char<1,8>>
+! CHECK-NEXT:     hlfir.destroy %[[VAL_7]] : !hlfir.expr<!fir.char<1,?>>
+! CHECK-NEXT:     return
+! CHECK-NEXT:   }
+subroutine trim_test(c)
+  character(*) :: c
+  character(8) :: tc
+
+  tc = trim(c)
+end subroutine
+
diff --git a/flang/test/Lower/volatile-string.f90 b/flang/test/Lower/volatile-string.f90
index f263db7abb5fc..8f392dfab8287 100644
--- a/flang/test/Lower/volatile-string.f90
+++ b/flang/test/Lower/volatile-string.f90
@@ -22,67 +22,56 @@ subroutine assign_different_length(string)
 end program
 
 ! CHECK-LABEL:   func.func @_QQmain() attributes {fir.bindc_name = "P"} {
-! CHECK:           %[[VAL_0:.*]] = arith.constant 11 : i32
-! CHECK:           %[[VAL_1:.*]] = arith.constant 0 : index
-! CHECK:           %[[VAL_2:.*]] = arith.constant true
-! CHECK:           %[[VAL_3:.*]] = arith.constant 10 : i32
-! CHECK:           %[[VAL_4:.*]] = arith.constant 3 : i32
-! CHECK:           %[[VAL_5:.*]] = arith.constant false
-! CHECK:           %[[VAL_6:.*]] = arith.constant 1 : index
-! CHECK:           %[[VAL_7:.*]] = arith.constant 3 : index
-! CHECK:           %[[VAL_8:.*]] = fir.alloca !fir.box<!fir.heap<!fir.char<1,?>>>
-! CHECK:           %[[VAL_9:.*]] = fir.alloca !fir.box<!fir.heap<!fir.char<1,3>>>
-! CHECK:           %[[VAL_10:.*]] = fir.alloca i32 {bindc_name = "i", uniq_name = "_QFEi"}
-! CHECK:           %[[VAL_11:.*]]:2 = hlfir.declare %[[VAL_10]] {uniq_name = "_QFEi"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
-! CHECK:           %[[VAL_12:.*]] = fir.alloca !fir.char<1,3> {bindc_name = "nonvolatile_string", uniq_name = "_QFEnonvolatile_string"}
-! CHECK:           %[[VAL_13:.*]]:2 = hlfir.declare %[[VAL_12]] typeparams %[[VAL_7]] {uniq_name = "_QFEnonvolatile_string"} : (!fir.ref<!fir.char<1,3>>, index) -> (!fir.ref<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>>)
-! CHECK:           %[[VAL_14:.*]] = fir.address_of(@_QFEstring) : !fir.ref<!fir.char<1,3>>
-! CHECK:           %[[VAL_15:.*]] = fir.volatile_cast %[[VAL_14]] : (!fir.ref<!fir.char<1,3>>) -> !fir.ref<!fir.char<1,3>, volatile>
-! CHECK:           %[[VAL_16:.*]]:2 = hlfir.declare %[[VAL_15]] typeparams %[[VAL_7]] {fortran_attrs = #fir.var_attrs<volatile>, uniq_name = "_QFEstring"} : (!fir.ref<!fir.char<1,3>, volatile>, index) -> (!fir.ref<!fir.char<1,3>, volatile>, !fir.ref<!fir.char<1,3>, volatile>)
-! CHECK:           %[[VAL_17:.*]] = fir.volatile_cast %[[VAL_16]]#0 : (!fir.ref<!fir.char<1,3>, volatile>) -> !fir.ref<!fir.char<1,3>>
-! CHECK:           %[[VAL_18:.*]] = fir.emboxchar %[[VAL_17]], %[[VAL_7]] : (!fir.ref<!fir.char<1,3>>, index) -> !fir.boxchar<1>
-! CHECK:           fir.call @_QFPassign_same_length(%[[VAL_18]]) fastmath<contract> : (!fir.boxchar<1>) -> ()
-! CHECK:           fir.call @_QFPassign_different_length(%[[VAL_18]]) fastmath<contract> : (!fir.boxchar<1>) -> ()
-! CHECK:           %[[VAL_19:.*]] = fir.address_of(@_QQclX6F) : !fir.ref<!fir.char<1>>
-! CHECK:           %[[VAL_20:.*]]:2 = hlfir.declare %[[VAL_19]] typeparams %[[VAL_6]] {fortran_attrs = #fir.var_attrs<parameter>, uniq_name = "_QQclX6F"} : (!fir.ref<!fir.char<1>>, index) -> (!fir.ref<!fir.char<1>>, !fir.ref<!fir.char<1>>)
-! CHECK:           %[[VAL_21:.*]] = fir.convert %[[VAL_17]] : (!fir.ref<!fir.char<1,3>>) -> !fir.ref<i8>
-! CHECK:           %[[VAL_22:.*]] = fir.convert %[[VAL_7]] : (index) -> i64
-! CHECK:           %[[VAL_23:.*]] = fir.convert %[[VAL_20]]#0 : (!fir.ref<!fir.char<1>>) -> !fir.ref<i8>
-! CHECK:           %[[VAL_24:.*]] = fir.convert %[[VAL_6]] : (index) -> i64
-! CHECK:           %[[VAL_25:.*]] = fir.call @_FortranAIndex1(%[[VAL_21]], %[[VAL_22]], %[[VAL_23]], %[[VAL_24]], %[[VAL_5]]) fastmath<contract> : (!fir.ref<i8>, i64, !fir.ref<i8>, i64, i1) -> i64
-! CHECK:           %[[VAL_26:.*]] = fir.convert %[[VAL_25]] : (i64) -> i32
-! CHECK:           hlfir.assign %[[VAL_26]] to %[[VAL_11]]#0 : i32, !fir.ref<i32>
-! CHECK:           hlfir.assign %[[VAL_4]] to %[[VAL_11]]#0 : i32, !fir.ref<i32>
-! CHECK:           %[[VAL_27:.*]] = fir.embox %[[VAL_16]]#0 : (!fir.ref<!fir.char<1,3>, volatile>) -> !fir.box<!fir.char<1,3>, volatile>
-! CHECK:           %[[VAL_28:.*]] = fir.zero_bits !fir.heap<!fir.char<1,3>>
-! CHECK:           %[[VAL_29:.*]] = fir.embox %[[VAL_28]] : (!fir.heap<!fir.char<1,3>>) -> !fir.box<!fir.heap<!fir.char<1,3>>>
-! CHECK:           fir.store %[[VAL_29]] to %[[VAL_9]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,3>>>>
-! CHECK:           %[[VAL_30:.*]] = fir.address_of(
-! CHECK:           %[[VAL_31:.*]] = fir.convert %[[VAL_9]] : (!fir.ref<!fir.box<!fir.heap<!fir.char<1,3>>>>) -> !fir.ref<!fir.box<none>>
-! CHECK:           %[[VAL_32:.*]] = fir.volatile_cast %[[VAL_27]] : (!fir.box<!fir.char<1,3>, volatile>) -> !fir.box<!fir.char<1,3>>
-! CHECK:           %[[VAL_33:.*]] = fir.convert %[[VAL_32]] : (!fir.box<!fir.char<1,3>>) -> !fir.box<none>
-! CHECK:           %[[VAL_34:.*]] = fir.convert %[[VAL_30]] : (!fir.ref<!fir.char<1,{{.*}}>>) -> !fir.ref<i8>
-! CHECK:           fir.call @_FortranAAdjustl(%[[VAL_31]], %[[VAL_33]], %[[VAL_34]], %[[VAL_3]]) fastmath<contract> : (!fir.ref<!fir.box<none>>, !fir.box<none>, !fir.ref<i8>, i32) -> ()
-! CHECK:           %[[VAL_35:.*]] = fir.load %[[VAL_9]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,3>>>>
-! CHECK:           %[[VAL_36:.*]] = fir.box_elesize %[[VAL_35]] : (!fir.box<!fir.heap<!fir.char<1,3>>>) -> index
-! CHECK:           %[[VAL_37:.*]] = fir.box_addr %[[VAL_35]] : (!fir.box<!fir.heap<!fir.char<1,3>>>) -> !fir.heap<!fir.char<1,3>>
-! CHECK:           %[[VAL_38:.*]]:2 = hlfir.declare %[[VAL_37]] typeparams %[[VAL_36]] {uniq_name = ".tmp.intrinsic_result"} : (!fir.heap<!fir.char<1,3>>, index) -> (!fir.heap<!fir.char<1,3>>, !fir.heap<!fir.char<1,3>>)
-! CHECK:           %[[VAL_39:.*]] = hlfir.as_expr %[[VAL_38]]#0 move %[[VAL_2]] : (!fir.heap<!fir.char<1,3>>, i1) -> !hlfir.expr<!fir.char<1,3>>
-! CHECK:           hlfir.assign %[[VAL_39]] to %[[VAL_16]]#0 : !hlfir.expr<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>, volatile>
-! CHECK:           hlfir.destroy %[[VAL_39]] : !hlfir.expr<!fir.char<1,3>>
-! CHECK:           %[[VAL_40:.*]] = fir.zero_bits !fir.heap<!fir.char<1,?>>
-! CHECK:           %[[VAL_41:.*]] = fir.embox %[[VAL_40]] typeparams %[[VAL_1]] : (!fir.heap<!fir.char<1,?>>, index) -> !fir.box<!fir.heap<!fir.char<1,?>>>
-! CHECK:           fir.store %[[VAL_41]] to %[[VAL_8]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,?>>>>
-! CHECK:           %[[VAL_42:.*]] = fir.convert %[[VAL_8]] : (!fir.ref<!fir.box<!fir.heap<!fir.char<1,?>>>>) -> !fir.ref<!fir.box<none>>
-! CHECK:           fir.call @_FortranATrim(%[[VAL_42]], %[[VAL_33]], %[[VAL_34]], %[[VAL_0]]) fastmath<contract> : (!fir.ref<!fir.box<none>>, !fir.box<none>, !fir.ref<i8>, i32) -> ()
-! CHECK:           %[[VAL_43:.*]] = fir.load %[[VAL_8]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,?>>>>
-! CHECK:           %[[VAL_44:.*]] = fir.box_elesize %[[VAL_43]] : (!fir.box<!fir.heap<!fir.char<1,?>>>) -> index
-! CHECK:           %[[VAL_45:.*]] = fir.box_addr %[[VAL_43]] : (!fir.box<!fir.heap<!fir.char<1,?>>>) -> !fir.heap<!fir.char<1,?>>
-! CHECK:           %[[VAL_46:.*]]:2 = hlfir.declare %[[VAL_45]] typeparams %[[VAL_44]] {uniq_name = ".tmp.intrinsic_result"} : (!fir.heap<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.heap<!fir.char<1,?>>)
-! CHECK:           %[[VAL_47:.*]] = hlfir.as_expr %[[VAL_46]]#0 move %[[VAL_2]] : (!fir.boxchar<1>, i1) -> !hlfir.expr<!fir.char<1,?>>
-! CHECK:           hlfir.assign %[[VAL_47]] to %[[VAL_13]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.ref<!fir.char<1,3>>
-! CHECK:           hlfir.destroy %[[VAL_47]] : !hlfir.expr<!fir.char<1,?>>
-! CHECK:           hlfir.assign %[[VAL_16]]#0 to %[[VAL_13]]#0 : !fir.ref<!fir.char<1,3>, volatile>, !fir.ref<!fir.char<1,3>>
+! CHECK:           %[[VAL_0:.*]] = arith.constant true
+! CHECK:           %[[VAL_1:.*]] = arith.constant 10 : i32
+! CHECK:           %[[VAL_2:.*]] = arith.constant 3 : i32
+! CHECK:           %[[VAL_3:.*]] = arith.constant false
+! CHECK:           %[[VAL_4:.*]] = arith.constant 1 : index
+! CHECK:           %[[VAL_5:.*]] = arith.constant 3 : index
+! CHECK:           %[[VAL_6:.*]] = fir.alloca !fir.box<!fir.heap<!fir.char<1,3>>>
+! CHECK:           %[[VAL_7:.*]] = fir.dummy_scope : !fir.dscope
+! CHECK:           %[[VAL_8:.*]] = fir.alloca i32 {bindc_name = "i", uniq_name = "_QFEi"}
+! CHECK:           %[[VAL_9:.*]]:2 = hlfir.declare %[[VAL_8]] {uniq_name = "_QFEi"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+! CHECK:           %[[VAL_10:.*]] = fir.alloca !fir.char<1,3> {bindc_name = "nonvolatile_string", uniq_name = "_QFEnonvolatile_string"}
+! CHECK:           %[[VAL_11:.*]]:2 = hlfir.declare %[[VAL_10]] typeparams %[[VAL_5]] {uniq_name = "_QFEnonvolatile_string"} : (!fir.ref<!fir.char<1,3>>, index) -> (!fir.ref<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>>)
+! CHECK:           %[[VAL_12:.*]] = fir.address_of(@_QFEstring) : !fir.ref<!fir.char<1,3>>
+! CHECK:           %[[VAL_13:.*]] = fir.volatile_cast %[[VAL_12]] : (!fir.ref<!fir.char<1,3>>) -> !fir.ref<!fir.char<1,3>, volatile>
+! CHECK:           %[[VAL_14:.*]]:2 = hlfir.declare %[[VAL_13]] typeparams %[[VAL_5]] {fortran_attrs = #fir.var_attrs<volatile>, uniq_name = "_QFEstring"} : (!fir.ref<!fir.char<1,3>, volatile>, index) -> (!fir.ref<!fir.char<1,3>, volatile>, !fir.ref<!fir.char<1,3>, volatile>)
+! CHECK:           %[[VAL_15:.*]] = fir.volatile_cast %[[VAL_14]]#0 : (!fir.ref<!fir.char<1,3>, volatile>) -> !fir.ref<!fir.char<1,3>>
+! CHECK:           %[[VAL_16:.*]] = fir.emboxchar %[[VAL_15]], %[[VAL_5]] : (!fir.ref<!fir.char<1,3>>, index) -> !fir.boxchar<1>
+! CHECK:           fir.call @_QFPassign_same_length(%[[VAL_16]]) fastmath<contract> : (!fir.boxchar<1>) -> ()
+! CHECK:           fir.call @_QFPassign_different_length(%[[VAL_16]]) fastmath<contract> : (!fir.boxchar<1>) -> ()
+! CHECK:           %[[VAL_17:.*]] = fir.address_of(@_QQclX6F) : !fir.ref<!fir.char<1>>
+! CHECK:           %[[VAL_18:.*]]:2 = hlfir.declare %[[VAL_17]] typeparams %[[VAL_4]] {fortran_attrs = #fir.var_attrs<parameter>, uniq_name = "_QQclX6F"} : (!fir.ref<!fir.char<1>>, index) -> (!fir.ref<!fir.char<1>>, !fir.ref<!fir.char<1>>)
+! CHECK:           %[[VAL_19:.*]] = fir.convert %[[VAL_15]] : (!fir.ref<!fir.char<1,3>>) -> !fir.ref<i8>
+! CHECK:           %[[VAL_20:.*]] = fir.convert %[[VAL_5]] : (index) -> i64
+! CHECK:           %[[VAL_21:.*]] = fir.convert %[[VAL_18]]#0 : (!fir.ref<!fir.char<1>>) -> !fir.ref<i8>
+! CHECK:           %[[VAL_22:.*]] = fir.convert %[[VAL_4]] : (index) -> i64
+! CHECK:           %[[VAL_23:.*]] = fir.call @_FortranAIndex1(%[[VAL_19]], %[[VAL_20]], %[[VAL_21]], %[[VAL_22]], %[[VAL_3]]) fastmath<contract> : (!fir.ref<i8>, i64, !fir.ref<i8>, i64, i1) -> i64
+! CHECK:           %[[VAL_24:.*]] = fir.convert %[[VAL_23]] : (i64) -> i32
+! CHECK:           hlfir.assign %[[VAL_24]] to %[[VAL_9]]#0 : i32, !fir.ref<i32>
+! CHECK:           hlfir.assign %[[VAL_2]] to %[[VAL_9]]#0 : i32, !fir.ref<i32>
+! CHECK:           %[[VAL_25:.*]] = fir.embox %[[VAL_14]]#0 : (!fir.ref<!fir.char<1,3>, volatile>) -> !fir.box<!fir.char<1,3>, volatile>
+! CHECK:           %[[VAL_26:.*]] = fir.zero_bits !fir.heap<!fir.char<1,3>>
+! CHECK:           %[[VAL_27:.*]] = fir.embox %[[VAL_26]] : (!fir.heap<!fir.char<1,3>>) -> !fir.box<!fir.heap<!fir.char<1,3>>>
+! CHECK:           fir.store %[[VAL_27]] to %[[VAL_6]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,3>>>>
+! CHECK:           %[[VAL_28:.*]] = fir.address_of(
+! CHECK:           %[[VAL_29:.*]] = fir.convert %[[VAL_6]] : (!fir.ref<!fir.box<!fir.heap<!fir.char<1,3>>>>) -> !fir.ref<!fir.box<none>>
+! CHECK:           %[[VAL_30:.*]] = fir.volatile_cast %[[VAL_25]] : (!fir.box<!fir.char<1,3>, volatile>) -> !fir.box<!fir.char<1,3>>
+! CHECK:           %[[VAL_31:.*]] = fir.convert %[[VAL_30]] : (!fir.box<!fir.char<1,3>>) -> !fir.box<none>
+! CHECK:           %[[VAL_32:.*]] = fir.convert %[[VAL_28]] : (!fir.ref<!fir.char<1,{{.*}}>>) -> !fir.ref<i8>
+! CHECK:           fir.call @_FortranAAdjustl(%[[VAL_29]], %[[VAL_31]], %[[VAL_32]], %[[VAL_1]]) fastmath<contract> : (!fir.ref<!fir.box<none>>, !fir.box<none>, !fir.ref<i8>, i32) -> ()
+! CHECK:           %[[VAL_33:.*]] = fir.load %[[VAL_6]] : !fir.ref<!fir.box<!fir.heap<!fir.char<1,3>>>>
+! CHECK:           %[[VAL_34:.*]] = fir.box_elesize %[[VAL_33]] : (!fir.box<!fir.heap<!fir.char<1,3>>>) -> index
+! CHECK:           %[[VAL_35:.*]] = fir.box_addr %[[VAL_33]] : (!fir.box<!fir.heap<!fir.char<1,3>>>) -> !fir.heap<!fir.char<1,3>>
+! CHECK:           %[[VAL_36:.*]]:2 = hlfir.declare %[[VAL_35]] typeparams %[[VAL_34]] {uniq_name = ".tmp.intrinsic_result"} : (!fir.heap<!fir.char<1,3>>, index) -> (!fir.heap<!fir.char<1,3>>, !fir.heap<!fir.char<1,3>>)
+! CHECK:           %[[VAL_37:.*]] = hlfir.as_expr %[[VAL_36]]#0 move %[[VAL_0]] : (!fir.heap<!fir.char<1,3>>, i1) -> !hlfir.expr<!fir.char<1,3>>
+! CHECK:           hlfir.assign %[[VAL_37]] to %[[VAL_14]]#0 : !hlfir.expr<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>, volatile>
+! CHECK:           hlfir.destroy %[[VAL_37]] : !hlfir.expr<!fir.char<1,3>>
+! CHECK:           %[[VAL_38:.*]] = hlfir.char_trim %[[VAL_14]]#0 : (!fir.ref<!fir.char<1,3>, volatile>) -> !hlfir.expr<!fir.char<1,3>>
+! CHECK:           hlfir.assign %[[VAL_38]] to %[[VAL_11]]#0 : !hlfir.expr<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>>
+! CHECK:           hlfir.destroy %[[VAL_38]] : !hlfir.expr<!fir.char<1,3>>
+! CHECK:           hlfir.assign %[[VAL_14]]#0 to %[[VAL_11]]#0 : !fir.ref<!fir.char<1,3>, volatile>, !fir.ref<!fir.char<1,3>>
 ! CHECK:           return
 ! CHECK:         }
 

>From cc806966fb25006c40ce89f152bfc5ad13ce5ab0 Mon Sep 17 00:00:00 2001
From: Leandro Lupori <leandro.lupori at linaro.org>
Date: Wed, 3 Sep 2025 13:22:38 -0300
Subject: [PATCH 2/2] Change result char type length to unknown

The runtime Trim function allocates the result, that may have a
different length than its input character string.
---
 flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp |  8 ++------
 flang/test/Lower/HLFIR/trim.f90           | 10 ++++++++++
 flang/test/Lower/volatile-string.f90      |  6 +++---
 3 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
index 6a2a28e3b6832..6f0b59db2383d 100644
--- a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
+++ b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
@@ -860,15 +860,11 @@ void hlfir::CmpCharOp::getEffects(
 
 void hlfir::CharTrimOp::build(mlir::OpBuilder &builder,
                               mlir::OperationState &result, mlir::Value chr) {
-  fir::CharacterType::LenType len;
-  if (auto cstLen = getCharacterLengthIfStatic(chr.getType()))
-    len = *cstLen;
-  else
-    len = fir::CharacterType::unknownLen();
   unsigned kind = getCharacterKind(chr.getType());
   auto resultType = hlfir::ExprType::get(
       builder.getContext(), hlfir::ExprType::Shape{},
-      fir::CharacterType::get(builder.getContext(), kind, len),
+      fir::CharacterType::get(builder.getContext(), kind,
+                              fir::CharacterType::unknownLen()),
       /*polymorphic=*/false);
   build(builder, result, resultType, chr);
 }
diff --git a/flang/test/Lower/HLFIR/trim.f90 b/flang/test/Lower/HLFIR/trim.f90
index ea1bd4fadead2..d09e6c58cb012 100644
--- a/flang/test/Lower/HLFIR/trim.f90
+++ b/flang/test/Lower/HLFIR/trim.f90
@@ -20,3 +20,13 @@ subroutine trim_test(c)
   tc = trim(c)
 end subroutine
 
+! Test trim with fixed length character.
+! The length of the returned character type must be unknown.
+! CHECK-LABEL:  func.func @_QPtrim_test2(
+! CHECK:          hlfir.char_trim %{{.*}}#0 : (!fir.ref<!fir.char<1,8>>) -> !hlfir.expr<!fir.char<1,?>>
+subroutine trim_test2(c)
+  character(8) :: c
+  character(8) :: tc
+
+  tc = trim(c)
+end subroutine
diff --git a/flang/test/Lower/volatile-string.f90 b/flang/test/Lower/volatile-string.f90
index 8f392dfab8287..38c29b477169c 100644
--- a/flang/test/Lower/volatile-string.f90
+++ b/flang/test/Lower/volatile-string.f90
@@ -68,9 +68,9 @@ subroutine assign_different_length(string)
 ! CHECK:           %[[VAL_37:.*]] = hlfir.as_expr %[[VAL_36]]#0 move %[[VAL_0]] : (!fir.heap<!fir.char<1,3>>, i1) -> !hlfir.expr<!fir.char<1,3>>
 ! CHECK:           hlfir.assign %[[VAL_37]] to %[[VAL_14]]#0 : !hlfir.expr<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>, volatile>
 ! CHECK:           hlfir.destroy %[[VAL_37]] : !hlfir.expr<!fir.char<1,3>>
-! CHECK:           %[[VAL_38:.*]] = hlfir.char_trim %[[VAL_14]]#0 : (!fir.ref<!fir.char<1,3>, volatile>) -> !hlfir.expr<!fir.char<1,3>>
-! CHECK:           hlfir.assign %[[VAL_38]] to %[[VAL_11]]#0 : !hlfir.expr<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>>
-! CHECK:           hlfir.destroy %[[VAL_38]] : !hlfir.expr<!fir.char<1,3>>
+! CHECK:           %[[VAL_38:.*]] = hlfir.char_trim %[[VAL_14]]#0 : (!fir.ref<!fir.char<1,3>, volatile>) -> !hlfir.expr<!fir.char<1,?>>
+! CHECK:           hlfir.assign %[[VAL_38]] to %[[VAL_11]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.ref<!fir.char<1,3>>
+! CHECK:           hlfir.destroy %[[VAL_38]] : !hlfir.expr<!fir.char<1,?>>
 ! CHECK:           hlfir.assign %[[VAL_14]]#0 to %[[VAL_11]]#0 : !fir.ref<!fir.char<1,3>, volatile>, !fir.ref<!fir.char<1,3>>
 ! CHECK:           return
 ! CHECK:         }



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