Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -5444,9 +5444,6 @@
   HelpText<"Specify which frame pointers to retain.">, Values<"all,non-leaf,none">,
   NormalizedValuesScope<"CodeGenOptions::FramePointerKind">, NormalizedValues<["All", "NonLeaf", "None"]>,
   MarshallingInfoEnum<CodeGenOpts<"FramePointer">, "None">;
-def mreassociate : Flag<["-"], "mreassociate">,
-  HelpText<"Allow reassociation transformations for floating-point instructions">,
-  MarshallingInfoFlag<LangOpts<"AllowFPReassoc">>, ImpliedByAnyOf<[funsafe_math_optimizations.KeyPath]>;
 def mabi_EQ_ieeelongdouble : Flag<["-"], "mabi=ieeelongdouble">,
   HelpText<"Use IEEE 754 quadruple-precision for long double">,
   MarshallingInfoFlag<LangOpts<"PPCIEEELongDouble">>;
@@ -6054,6 +6051,9 @@
 
 let Flags = [CC1Option, FC1Option, NoDriverOption] in {
 
+def mreassociate : Flag<["-"], "mreassociate">,
+  HelpText<"Allow reassociation transformations for floating-point instructions">,
+  MarshallingInfoFlag<LangOpts<"AllowFPReassoc">>, ImpliedByAnyOf<[funsafe_math_optimizations.KeyPath]>;
 def menable_no_nans : Flag<["-"], "menable-no-nans">,
   HelpText<"Allow optimization to assume there are no NaNs.">,
   MarshallingInfoFlag<LangOpts<"NoHonorNaNs">>, ImpliedByAnyOf<[ffinite_math_only.KeyPath]>;
Index: clang/lib/Driver/ToolChains/Flang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Flang.cpp
+++ clang/lib/Driver/ToolChains/Flang.cpp
@@ -87,6 +87,7 @@
   bool HonorNaNs = true;
   bool ApproxFunc = false;
   bool SignedZeros = true;
+  bool AssociativeMath = false;
 
   if (const Arg *A = Args.getLastArg(options::OPT_ffp_contract)) {
     const StringRef Val = A->getValue();
@@ -136,6 +137,12 @@
     case options::OPT_fno_signed_zeros:
       SignedZeros = false;
       break;
+    case options::OPT_fassociative_math:
+      AssociativeMath = true;
+      break;
+    case options::OPT_fno_associative_math:
+      AssociativeMath = false;
+      break;
     }
 
     // If we handled this option claim it
@@ -156,6 +163,9 @@
 
   if (!SignedZeros)
     CmdArgs.push_back("-fno-signed-zeros");
+
+  if (AssociativeMath && !SignedZeros)
+    CmdArgs.push_back("-mreassociate");
 }
 
 void Flang::ConstructJob(Compilation &C, const JobAction &JA,
Index: flang/include/flang/Frontend/LangOptions.def
===================================================================
--- flang/include/flang/Frontend/LangOptions.def
+++ flang/include/flang/Frontend/LangOptions.def
@@ -29,6 +29,8 @@
 LANGOPT(ApproxFunc, 1, false)
 /// Allow optimizations that ignore the sign of floating point zeros
 LANGOPT(NoSignedZeros, 1, false)
+/// Allow reassociation transformations for floating-point instructions
+LANGOPT(AssociativeMath, 1, false)
 
 #undef LANGOPT
 #undef ENUM_LANGOPT
Index: flang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- flang/lib/Frontend/CompilerInvocation.cpp
+++ flang/lib/Frontend/CompilerInvocation.cpp
@@ -715,6 +715,12 @@
     opts.NoSignedZeros = true;
   }
 
+  if (const llvm::opt::Arg *a =
+          args.getLastArg(clang::driver::options::OPT_mreassociate)) {
+    diags.Report(diagUnimplemented) << a->getOption().getName();
+    opts.AssociativeMath = true;
+  }
+
   return true;
 }
 
Index: flang/test/Driver/driver-help.f90
===================================================================
--- flang/test/Driver/driver-help.f90
+++ flang/test/Driver/driver-help.f90
@@ -140,6 +140,7 @@
 ! HELP-FC1-NEXT: -mmlir <value>         Additional arguments to forward to MLIR's option processing
 ! HELP-FC1-NEXT: -module-dir <dir>      Put MODULE files in <dir>
 ! HELP-FC1-NEXT: -module-suffix <suffix> Use <suffix> as the suffix for module files (the default value is `.mod`)
+! HELP-FC1-NEXT: -mreassociate          Allow reassociation transformations for floating-point instructions
 ! HELP-FC1-NEXT: -mrelocation-model <value>
 ! HELP-FC1-NEXT:                        The relocation model to use
 ! HELP-FC1-NEXT: -nocpp                 Disable predefined and command line preprocessor macros
Index: flang/test/Driver/flang_fp_opts.f90
===================================================================
--- flang/test/Driver/flang_fp_opts.f90
+++ flang/test/Driver/flang_fp_opts.f90
@@ -6,9 +6,11 @@
 ! RUN:      -menable-no-nans \
 ! RUN:      -fapprox-func \
 ! RUN:      -fno-signed-zeros \
+! RUN:      -mreassociate \
 ! RUN:      %s 2>&1 | FileCheck %s
 ! CHECK: ffp-contract= is not currently implemented
 ! CHECK: menable-no-infs is not currently implemented
 ! CHECK: menable-no-nans is not currently implemented
 ! CHECK: fapprox-func is not currently implemented
 ! CHECK: fno-signed-zeros is not currently implemented
+! CHECK: mreassociate is not currently implemented
Index: flang/test/Driver/frontend-forwarding.f90
===================================================================
--- flang/test/Driver/frontend-forwarding.f90
+++ flang/test/Driver/frontend-forwarding.f90
@@ -13,6 +13,7 @@
 ! RUN:     -fno-honor-nans \
 ! RUN:     -fapprox-func \
 ! RUN:     -fno-signed-zeros \
+! RUN:     -fassociative-math \
 ! RUN:     -mllvm -print-before-all\
 ! RUN:     -P \
 ! RUN:   | FileCheck %s
@@ -28,5 +29,6 @@
 ! CHECK: "-menable-no-nans"
 ! CHECK: "-fapprox-func"
 ! CHECK: "-fno-signed-zeros"
+! CHECK: "-mreassociate"
 ! CHECK: "-fconvert=little-endian"
 ! CHECK:  "-mllvm" "-print-before-all"