Add implicit interfaces for function hooks in Fortran module by joewallwork · Pull Request #2809 · EnzymeAD/Enzyme

joewallwork · 2026-05-07T14:02:28Z

Closes #2808.
~~Merges into #2807.~~

As mentioned in the issue, it turns out that the interfacing to the special Enzyme function hooks can be done using implicit interfaces in Fortran. That is, you can get away without providing an explicit interface block like is done in the examples so long as you declare

external :: __enzyme_autodiff

for example.

Checklist

Add to Fortran enzyme module
Use in square example

Hooking up in the allocatableArraySimple example will require fixing #2820.

joewallwork · 2026-05-07T14:12:36Z

Huh, looks like ifx doesn't like externals with leading underscores. I hadn't tested this with that compiler yet (just flang).

…n module

joewallwork · 2026-05-11T16:17:23Z

Huh, looks like ifx doesn't like externals with leading underscores. I hadn't tested this with that compiler yet (just flang).

Fixed in 237ebc6 by prepending with f for the Fortran versions of the function hooks.

joewallwork · 2026-05-18T12:28:10Z

I don't understand why the square Fortran CI test is failing. I've set things up such that the enzyme.mod module file gets put in ${PROJECT_BINARY_DIR}/Fortran, which is used to define %loadFortran as an include in the Lit config. I can see the include getting picked up correctly in the CI failure but it still gives an error with opening the module file.
https://github.com/EnzymeAD/Enzyme/actions/runs/26032772064/job/76522827921?pr=2809

I don't see this error when building locally and running the test with IFX.

vchuravy · 2026-05-19T08:51:48Z

/home/runner/work/Enzyme/Enzyme/enzyme/test/Fortran/ReverseMode/square.f90(15): error #7013: This module file was not generated by any release of this compiler.   [ENZYME]

sigh gotta love ifx.

In the logs we also see

Building Fortran bindings
-- The Fortran compiler identification is GNU 11.4.0
-- Detecting Fortran compiler ABI info
-- Detecting Fortran compiler ABI info - done
-- Check for working Fortran compiler: /usr/bin/gfortran - skipped
-- Detecting Fortran/C Interface
-- Detecting Fortran/C Interface - Found GLOBAL and MODULE mangling
-- Verifying Fortran/C Compiler Compatibility
-- Verifying Fortran/C Compiler Compatibility - Success
Building Fortran tests

vchuravy · 2026-05-19T08:55:24Z

-! RUN: if [ %llvmver -ge 13 ]; then ifx -flto -O1 -c  %s -o /dev/stdout | %opt %loadEnzyme -enzyme -o %t && ifx -flto -O1 %t -o %t1 && %t1 | FileCheck %s; fi
-! RUN: if [ %llvmver -ge 13 ]; then ifx -flto -O2 -c  %s -o /dev/stdout | %opt %loadEnzyme -enzyme -o %t && ifx -flto -O2 %t -o %t1 && %t1 | FileCheck %s; fi
-! RUN: if [ %llvmver -ge 13 ]; then ifx -flto -O3 -c  %s -o /dev/stdout | %opt %loadEnzyme -enzyme -o %t && ifx -flto -O3 %t -o %t1 && %t1 | FileCheck %s; fi
+! RUN: if [ %llvmver -ge 13 ]; then ifx -flto -O0 -c %loadFortran %s -o /dev/stdout | %opt %loadEnzyme -enzyme -o %t && ifx -flto -O0 %t -o %t1 && %t1 | FileCheck %s; fi


! RUN: if [ %llvmver -ge 13 ]; then ifx -flto -O0 -c %loadFortran %s -o /dev/stdout | %opt %loadEnzyme -enzyme -o %t && ifx -flto -O0 %t -o %t1 && %t1 | FileCheck %s; fi

We should detect which fortran compiler we are using based CMAKE_FC_COMPILER_ID which should be IntelLLVM and then define a substition for %fc

Nice! Done in fa15388.

vchuravy · 2026-05-19T08:56:27Z

      run: |
        rm -rf build && mkdir build && cd build
-        cmake ../enzyme -GNinja -DCMAKE_BUILD_TYPE=${{ matrix.build }} -DLLVM_DIR=/usr/lib/llvm-${{ matrix.llvm }}/lib/cmake/llvm -DLLVM_EXTERNAL_LIT=`which lit` -DENZYME_IFX=ON
+        cmake ../enzyme -GNinja -DCMAKE_BUILD_TYPE=${{ matrix.build }} -DLLVM_DIR=/usr/lib/llvm-${{ matrix.llvm }}/lib/cmake/llvm -DLLVM_EXTERNAL_LIT=`which lit` -DENZYME_FORTRAN=ON -DENZYME_IFX=ON


-DCMAKE_FC_COMPILER=ifx and later we can generalize the workflow to also support flang

Done in b50179c.

Co-authored-by: Valentin Churavy <v.churavy@gmail.com>

joewallwork · 2026-05-19T15:38:29Z

Hm ifx still doesn't seem happy. I should have some time to debug later in the week.

vchuravy · 2026-05-19T19:30:50Z

Currently we test Fortran integration with LLVM 15, we eventually need to update that.

I just wanted to use an Enzyme build with LLVM 21 and ran into

The `opt -passname` syntax for the new pass manager is not supported, please use `opt -passes=<pipeline>` (or the `-p` alias for a more concise version).
See https://llvm.org/docs/NewPassManager.html#invoking-opt for more details on the pass pipeline syntax.

vchuravy · 2026-05-19T19:34:00Z

To debug the current failure:

/mnt/data/vchuravy/intel/2026.0/bin/ifx -flto -O0 -c -I/home/vchuravy/src/Enzyme/enzyme-core/build/modules /home/vchuravy/src/Enzyme/enzyme-core/enzyme/test/Fortran/ReverseMode/square.f90 -o /dev/stdout | llvm-dis

; Function Attrs: noinline nounwind optnone uwtable
define void @MAIN__() #0 {
alloca_2:
  %"$io_ctx" = alloca [8 x i64], align 8, !llfort.type_idx !5
  %"app_$DX" = alloca float, align 4, !llfort.type_idx !6
  %"app_$X" = alloca float, align 4, !llfort.type_idx !7
  %"var$1" = alloca i32, align 4, !llfort.type_idx !8
  %"(&)val$" = alloca [4 x i8], align 1, !llfort.type_idx !9
  %argblock = alloca <{ i64 }>, align 8, !llfort.type_idx !10
  %"var$2" = alloca i32, align 4, !llfort.type_idx !8
  %"(&)val$5" = alloca [4 x i8], align 1, !llfort.type_idx !11
  %argblock6 = alloca <{ i64 }>, align 8, !llfort.type_idx !10
  %func_result = call i32 @for_set_reentrancy(ptr @anon.f01f2640a9c3f724255ee7144b3336fc.0), !llfort.type_idx !8
  store float 3.000000e+00, ptr %"app_$X", align 4
  %func_result2 = call reassoc ninf nsz arcp contract afn float @math_mp_square_(ptr %"app_$X"), !llfort.type_idx !12
  store i64 0, ptr %"$io_ctx", align 8
  store [4 x i8] c"\1A\01\01\00", ptr %"(&)val$", align 1
  %BLKFIELD_float_ = getelementptr inbounds <{ i64 }>, ptr %argblock, i32 0, i32 0, !llfort.type_idx !13
  store float %func_result2, ptr %BLKFIELD_float_, align 4
  %func_result4 = call i32 (ptr, i32, i64, ptr, ptr, ...) @for_write_seq_lis(ptr %"$io_ctx", i32 -1, i64 2253038970797824, ptr %"(&)val$", ptr %argblock), !llfort.type_idx !8
  store float 0.000000e+00, ptr %"app_$DX", align 4
  call void @f__enzyme_autodiff_.t69p.t70p.t71p(ptr @math_mp_square_, ptr %"app_$X", ptr %"app_$DX"), !llfort.type_idx !14
  %"app_$DX_fetch.3" = load float, ptr %"app_$DX", align 4, !llfort.type_idx !6
  store i64 0, ptr %"$io_ctx", align 8
  store [4 x i8] c"\1A\01\01\00", ptr %"(&)val$5", align 1
  %BLKFIELD_float_7 = getelementptr inbounds <{ i64 }>, ptr %argblock6, i32 0, i32 0, !llfort.type_idx !15
  store float %"app_$DX_fetch.3", ptr %BLKFIELD_float_7, align 4
  %func_result9 = call i32 (ptr, i32, i64, ptr, ptr, ...) @for_write_seq_lis(ptr %"$io_ctx", i32 -1, i64 2253038970797824, ptr %"(&)val$5", ptr %argblock6), !llfort.type_idx !8
  ret void
}

; Function Attrs: noinline nounwind optnone uwtable
define internal void @f__enzyme_autodiff_.t69p.t70p.t71p(ptr %arg0, ptr %arg1, ptr %arg2) #0 {
wrap_start20:
  call void (...) @f__enzyme_autodiff_(ptr %arg0, ptr %arg1, ptr %arg2)
  ret void
}

declare void @f__enzyme_autodiff_(...)

So the additional indirection is hiding things.

vchuravy · 2026-05-19T19:40:00Z

So the issue only exists at -O0

at -O1

; Function Attrs: nounwind uwtable
define void @MAIN__() local_unnamed_addr #2 {
alloca_2:
  %"$io_ctx" = alloca [8 x i64], align 8, !llfort.type_idx !7
  %"app_$DX" = alloca float, align 4, !llfort.type_idx !8
  %"app_$X" = alloca float, align 4, !llfort.type_idx !9
  %"(&)val$" = alloca [4 x i8], align 1, !llfort.type_idx !10
  %argblock = alloca <{ i64 }>, align 8, !llfort.type_idx !11
  %"(&)val$7" = alloca [4 x i8], align 1, !llfort.type_idx !12
  %argblock8 = alloca <{ i64 }>, align 8, !llfort.type_idx !11
  %func_result = tail call i32 @for_set_fpe_(ptr nonnull @anon.f01f2640a9c3f724255ee7144b3336fc.0) #4, !llfort.type_idx !13
  %func_result2 = tail call i32 @for_set_reentrancy(ptr nonnull @anon.f01f2640a9c3f724255ee7144b3336fc.1) #4, !llfort.type_idx !13
  store float 3.000000e+00, ptr %"app_$X", align 4, !tbaa !14
  store i64 0, ptr %"$io_ctx", align 8, !tbaa !19
  %.fca.0.gep12 = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$", i64 0, i64 0
  store i8 26, ptr %.fca.0.gep12, align 1, !tbaa !19
  %.fca.1.gep13 = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$", i64 0, i64 1
  store i8 1, ptr %.fca.1.gep13, align 1, !tbaa !19
  %.fca.2.gep14 = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$", i64 0, i64 2
  store i8 1, ptr %.fca.2.gep14, align 1, !tbaa !19
  %.fca.3.gep15 = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$", i64 0, i64 3
  store i8 0, ptr %.fca.3.gep15, align 1, !tbaa !19
  %BLKFIELD_float_ = getelementptr inbounds nuw <{ i64 }>, ptr %argblock, i64 0, i32 0, !llfort.type_idx !20
  store float 9.000000e+00, ptr %BLKFIELD_float_, align 8, !tbaa !21
  %func_result6 = call i32 (ptr, i32, i64, ptr, ptr, ...) @for_write_seq_lis(ptr nonnull %"$io_ctx", i32 -1, i64 2253038970797824, ptr nonnull %"(&)val$", ptr nonnull %argblock) #4, !llfort.type_idx !13
  store float 0.000000e+00, ptr %"app_$DX", align 4, !tbaa !23
  call void (...) @f__enzyme_autodiff_(ptr nonnull @math_mp_square_, ptr nonnull %"app_$X", ptr nonnull %"app_$DX") #4
  %"app_$DX_fetch.3" = load float, ptr %"app_$DX", align 4, !tbaa !23, !llfort.type_idx !8
  store i64 0, ptr %"$io_ctx", align 8, !tbaa !19
  %.fca.0.gep = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$7", i64 0, i64 0
  store i8 26, ptr %.fca.0.gep, align 1, !tbaa !19
  %.fca.1.gep = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$7", i64 0, i64 1
  store i8 1, ptr %.fca.1.gep, align 1, !tbaa !19
  %.fca.2.gep = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$7", i64 0, i64 2
  store i8 1, ptr %.fca.2.gep, align 1, !tbaa !19
  %.fca.3.gep = getelementptr inbounds nuw [4 x i8], ptr %"(&)val$7", i64 0, i64 3
  store i8 0, ptr %.fca.3.gep, align 1, !tbaa !19
  %BLKFIELD_float_9 = getelementptr inbounds nuw <{ i64 }>, ptr %argblock8, i64 0, i32 0, !llfort.type_idx !25
  store float %"app_$DX_fetch.3", ptr %BLKFIELD_float_9, align 8, !tbaa !26
  %func_result11 = call i32 (ptr, i32, i64, ptr, ptr, ...) @for_write_seq_lis(ptr nonnull %"$io_ctx", i32 -1, i64 2253038970797824, ptr nonnull %"(&)val$7", ptr nonnull %argblock8) #4, !llfort.type_idx !13
  ret void
}

vchuravy · 2026-05-19T20:02:59Z

I was playing around with:

!DIR$ ATTRIBUTES FORCEINLINE :: enzyme_autodiff;
!DIR$ ATTRIBUTES FORCEINLINE :: enzyme_fwddiff;

and variations thereof, but nothing seems to stick.

Adding

    !DIR$ FORCEINLINE
    call enzyme_autodiff(square, x, dx);

does work but is kinda silly.

The options I see is:

Don't test -O0 -- meh
Add the callsite directive -- meh, and compiler dependent
Don't do the clever indirection -- sad

joewallwork · 2026-05-21T15:03:11Z

I was playing around with:
!DIR$ ATTRIBUTES FORCEINLINE :: enzyme_autodiff;
!DIR$ ATTRIBUTES FORCEINLINE :: enzyme_fwddiff;
and variations thereof, but nothing seems to stick.

Adding
    !DIR$ FORCEINLINE
    call enzyme_autodiff(square, x, dx);
does work but is kinda silly.

The options I see is:
1. Don't test `-O0` -- meh

2. Add the callsite directive -- meh, and compiler dependent

3. Don't do the clever indirection -- sad

Alas. My debugging today has also not really revealed any ways forward with ifx.

I'll work on setting up a flang CI so that we can test the bindings under that compiler (works fine for me so far) and I guess we can return to ifx later.

joewallwork added 2 commits May 7, 2026 14:11

Add enzyme_mod containing activity descriptor bindings

8052bde

Hook Fortran bindings up in build system

47c59bd

joewallwork self-assigned this May 7, 2026

joewallwork added enhancement New feature or request fortran Related to Enzyme's Fortran bindings labels May 7, 2026

joewallwork mentioned this pull request May 7, 2026

Create Fortran bindings module #2807

Merged

2 tasks

joewallwork added 4 commits May 7, 2026 15:21

Rename enzyme_mod->enzyme

27b7edc

Use implicit interface in square example

eec1139

Add bindings for __enzyme_autodiff and __enzyme_fwddiff to the Fortra…

b34ce86

…n module

Use __enzyme_autodiff binding in square example

3c11497

joewallwork force-pushed the 2808_fortran-implicit-interfaces branch from d249dc7 to 3c11497 Compare May 7, 2026 14:38

joewallwork changed the base branch from main to 2805_fortran-mod May 7, 2026 14:38

joewallwork mentioned this pull request May 11, 2026

Account for Fortran assumed shape #2821

Draft

Prepend function hooks with f

237ebc6

joewallwork marked this pull request as ready for review May 11, 2026 16:17

joewallwork requested review from vchuravy and wsmoses May 11, 2026 16:18

Trigger Fortran CI on changes to enzyme/Fortran

2338caf

joewallwork changed the title ~~Use implicit interfaces in Fortran examples~~ Add implicit interfaces for function hooks in Fortran module May 11, 2026

Base automatically changed from 2805_fortran-mod to main May 15, 2026 16:06

joewallwork and others added 8 commits May 18, 2026 07:54

Merge branch 'main' into 2808_fortran-implicit-interfaces

3219957

Reorder to compile Fortran module before tests

16090da

Drop duplicate option

b7685e0

Build with ENZYME_FORTRAN=ON in CI

96ddb90

Only build Fortran tests if ENZYME_FORTRAN

7a84258

Remove CMake commands not needed

89abe9f

Use enzyme.mod in Fortran square test

981e5c0

Add back in CMake from Fortran subdir

9822b1c

joewallwork added 2 commits May 18, 2026 12:09

Drop unrelated editor changes

48db7db

Fixes for root CMakeLists

9f65061

vchuravy reviewed May 18, 2026

View reviewed changes

Comment thread enzyme/Fortran/enzyme.f90 Outdated

Add messages for building Fortran bindings and tests

ebcfca1

joewallwork added 4 commits May 18, 2026 13:31

Move message into Fortran subdir

db7cbff

Make EnzymeFortran a shared object

be84f81

Try putting module in modules dir

e6e07ca

Introduce another module for function hooks to facilitate aliasing

2be33a7