[flang-commits] [flang] [flang] Add comdats to functions with linkonce linkage (PR #66516)

[David Truby via flang-commits]

https://github.com/DavidTruby created https://github.com/llvm/llvm-project/pull/66516

This fixes a bug where functions generated by the MLIR Math dialect, for
example ipowi, would fail to link with link.exe on Windows due to having
linkonce linkage but no associated comdat. Adding the comdat on ELF also
allows linkers to perform better garbage collection in the binary.

Simply adding comdats to all functions with this linkage type should
also cover future cases where linkonce or linkonce_odr functions might
be necessary.


>From 492a1607c34b5aafad000beebad60b619f22bd01 Mon Sep 17 00:00:00 2001
From: David Truby <David.Truby at arm.com>
Date: Fri, 15 Sep 2023 14:08:51 +0000
Subject: [PATCH] [flang] Add comdats to functions with linkonce linkage

This fixes a bug where functions generated by the MLIR Math dialect, for
example ipowi, would fail to link with link.exe on Windows due to having
linkonce linkage but no associated comdat. Adding the comdat on ELF also
allows linkers to perform better garbage collection in the binary.

Simply adding comdats to all functions with this linkage type should
also cover future cases where linkonce or linkonce_odr functions might
be necessary.
---
 flang/lib/Optimizer/CodeGen/CodeGen.cpp |  9 ++++++
 flang/test/Fir/comdat.fir               | 41 +++++++++++++++++++++++++
 flang/test/Intrinsics/math-codegen.fir  |  8 ++++-
 3 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 flang/test/Fir/comdat.fir

diff --git a/flang/lib/Optimizer/CodeGen/CodeGen.cpp b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
index 0ec7e570395e89c..6a6a10f632648cd 100644
--- a/flang/lib/Optimizer/CodeGen/CodeGen.cpp
+++ b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
@@ -34,6 +34,7 @@
 #include "mlir/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.h"
 #include "mlir/Conversion/VectorToLLVM/ConvertVectorToLLVM.h"
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
+#include "mlir/Dialect/LLVMIR/Transforms/AddComdats.h"
 #include "mlir/Dialect/OpenACC/OpenACC.h"
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
 #include "mlir/IR/BuiltinTypes.h"
@@ -3861,6 +3862,14 @@ class FIRToLLVMLowering
                                                std::move(pattern)))) {
       signalPassFailure();
     }
+
+    // Run pass to add comdats to functions that have weak linkage on relevant platforms
+    if (fir::getTargetTriple(mod).supportsCOMDAT()) {
+      mlir::OpPassManager comdatPM("builtin.module");
+      comdatPM.addPass(mlir::LLVM::createLLVMAddComdats());
+      if (mlir::failed(runPipeline(comdatPM, mod)))
+        return signalPassFailure();
+    }
   }
 
 private:
diff --git a/flang/test/Fir/comdat.fir b/flang/test/Fir/comdat.fir
new file mode 100644
index 000000000000000..2f5da505e4903f5
--- /dev/null
+++ b/flang/test/Fir/comdat.fir
@@ -0,0 +1,41 @@
+
+// RUN: fir-opt %s --fir-to-llvm-ir="target=x86_64-unknown-linux-gnu" | FileCheck %s --check-prefixes="CHECK-COMDAT"
+// RUN: fir-opt %s --fir-to-llvm-ir="target=x86_64-pc-windows-msvc" | FileCheck %s --check-prefixes="CHECK-COMDAT"
+// RUN: fir-opt %s --fir-to-llvm-ir="target=aarch64-apple-darwin" | FileCheck %s --check-prefixes="CHECK-NOCOMDAT"
+// RUN: fir-opt %s --fir-to-llvm-ir="target=powerpc64-ibm-aix" | FileCheck %s --check-prefixes="CHECK-NOCOMDAT"
+
+// CHECK-COMDAT: llvm.func linkonce @fun_linkonce(%arg0: i32) -> i32 comdat(@__llvm_comdat::@fun_linkonce)
+// CHECK-NOCOMDAT: llvm.func linkonce @fun_linkonce(%arg0: i32) -> i32 {
+func.func @fun_linkonce(%arg0: i32) -> i32 attributes {llvm.linkage = #llvm.linkage<linkonce>} {
+  return %arg0 : i32
+}
+
+// CHECK-COMDAT: llvm.func linkonce_odr @fun_linkonce_odr(%arg0: i32) -> i32 comdat(@__llvm_comdat::@fun_linkonce_odr)
+// CHECK-NOCOMDAT: llvm.func linkonce_odr @fun_linkonce_odr(%arg0: i32) -> i32 {
+func.func @fun_linkonce_odr(%arg0: i32) -> i32 attributes {llvm.linkage = #llvm.linkage<linkonce_odr>} {
+  return %arg0 : i32
+}
+
+// CHECK-COMDAT:  llvm.mlir.global linkonce constant @global_linkonce() comdat(@__llvm_comdat::@global_linkonce) {addr_space = 0 : i32} : i32 
+// CHECK-NOCOMDAT:  llvm.mlir.global linkonce constant @global_linkonce() {addr_space = 0 : i32} : i32  {
+fir.global linkonce @global_linkonce constant : i32 {
+  %0 = arith.constant 0 : i32
+  fir.has_value %0 : i32
+}
+
+// CHECK-COMDAT: llvm.comdat @__llvm_comdat {
+// CHECK-COMDAT: llvm.comdat_selector @fun_linkonce_odr any
+// CHECK-COMDAT: llvm.comdat_selector @fun_linkonce any
+// CHECK-COMDAT: llvm.comdat_selector @global_linkonce any
+// CHECK-COMDAT: llvm.comdat_selector @global_linkonce_odr any
+
+// CHECK-NOCOMDAT-NOT: llvm.comdat
+// CHECK-NOCOMDAT-NOT: llvm.comdat_selector
+
+
+// CHECK-COMDAT:  llvm.mlir.global linkonce_odr constant @global_linkonce_odr() comdat(@__llvm_comdat::@global_linkonce_odr) {addr_space = 0 : i32} : i32 
+// CHECK-NOCOMDAT:  llvm.mlir.global linkonce_odr constant @global_linkonce_odr() {addr_space = 0 : i32} : i32 { 
+fir.global linkonce_odr @global_linkonce_odr constant : i32 {
+  %0 = arith.constant 0 : i32
+  fir.has_value %0 : i32
+}
\ No newline at end of file
diff --git a/flang/test/Intrinsics/math-codegen.fir b/flang/test/Intrinsics/math-codegen.fir
index 0af896adf3226fd..62d841253075e80 100644
--- a/flang/test/Intrinsics/math-codegen.fir
+++ b/flang/test/Intrinsics/math-codegen.fir
@@ -1467,9 +1467,15 @@ func.func private @llvm.powi.f64.i32(f64, i32) -> f64
 func.func private @pow(f64, f64) -> f64
 
 //--- exponentiation_integer.fir
-// RUN: fir-opt %t/exponentiation_integer.fir --fir-to-llvm-ir="target=x86_64-unknown-linux-gnu" | FileCheck %t/exponentiation_integer.fir
+// RUN: fir-opt %t/exponentiation_integer.fir --fir-to-llvm-ir="target=x86_64-unknown-linux-gnu" | FileCheck %t/exponentiation_integer.fir --check-prefixes="CHECK,CHECK-COMDAT"
+// RUN: fir-opt %t/exponentiation_integer.fir --fir-to-llvm-ir="target=x86_64-pc-windows-msvc" | FileCheck %t/exponentiation_integer.fir --check-prefixes="CHECK,CHECK-COMDAT"
+// RUN: fir-opt %t/exponentiation_integer.fir --fir-to-llvm-ir="target=aarch64-apple-darwin" | FileCheck %t/exponentiation_integer.fir --check-prefixes="CHECK,CHECK-NOCOMDAT"
+// CHECK-COMDAT: llvm.comdat_selector @__mlir_math_ipowi_i32 any
+// CHECK-NOCOMDAT-NOT: llvm.comdat_selector @__mlir_math_ipowi_i32 any
 // CHECK: @_QPtest_int4
 // CHECK: llvm.call @__mlir_math_ipowi_i32({{%[A-Za-z0-9._]+}}, {{%[A-Za-z0-9._]+}}) : (i32, i32) -> i32
+// CHECK-COMDAT: llvm.func linkonce_odr @__mlir_math_ipowi_i32(%arg0: i32, %arg1: i32) -> i32 comdat(@__llvm_comdat::@__mlir_math_ipowi_i32)
+// CHECK-NOCOMDAT: llvm.func linkonce_odr @__mlir_math_ipowi_i32(%arg0: i32, %arg1: i32) -> i32
 
 func.func @_QPtest_int4(%arg0: !fir.ref<i32> {fir.bindc_name = "x"}, %arg1: !fir.ref<i32> {fir.bindc_name = "y"}, %arg2: !fir.ref<i32> {fir.bindc_name = "z"}) {
   %0 = fir.load %arg0 : !fir.ref<i32>