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

--
Full diff: https://github.com/llvm/llvm-project/pull/66516.diff

3 Files Affected:

• (modified) flang/lib/Optimizer/CodeGen/CodeGen.cpp (+9)
• (added) flang/test/Fir/comdat.fir (+41)
• (modified) flang/test/Intrinsics/math-codegen.fir (+7-1)

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>