Index: cfe/trunk/include/clang/Driver/CC1Options.td
===================================================================
--- cfe/trunk/include/clang/Driver/CC1Options.td
+++ cfe/trunk/include/clang/Driver/CC1Options.td
@@ -263,6 +263,8 @@
 def menable_unsafe_fp_math : Flag<["-"], "menable-unsafe-fp-math">,
   HelpText<"Allow unsafe floating-point math optimizations which may decrease "
            "precision">;
+def mreassociate : Flag<["-"], "mreassociate">,
+  HelpText<"Allow reassociation transformations for floating-point instructions">;
 def mfloat_abi : Separate<["-"], "mfloat-abi">,
   HelpText<"The float ABI to use">;
 def mtp : Separate<["-"], "mtp">,
Index: cfe/trunk/include/clang/Frontend/CodeGenOptions.def
===================================================================
--- cfe/trunk/include/clang/Frontend/CodeGenOptions.def
+++ cfe/trunk/include/clang/Frontend/CodeGenOptions.def
@@ -117,6 +117,7 @@
 CODEGENOPT(NoImplicitFloat   , 1, 0) ///< Set when -mno-implicit-float is enabled.
 CODEGENOPT(NoInfsFPMath      , 1, 0) ///< Assume FP arguments, results not +-Inf.
 CODEGENOPT(NoSignedZeros     , 1, 0) ///< Allow ignoring the signedness of FP zero
+CODEGENOPT(Reassociate       , 1, 0) ///< Allow reassociation of FP math ops
 CODEGENOPT(ReciprocalMath    , 1, 0) ///< Allow FP divisions to be reassociated.
 CODEGENOPT(NoTrappingMath    , 1, 0) ///< Set when -fno-trapping-math is enabled.
 CODEGENOPT(NoNaNsFPMath      , 1, 0) ///< Assume FP arguments, results not NaN.
Index: cfe/trunk/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- cfe/trunk/lib/CodeGen/CodeGenFunction.cpp
+++ cfe/trunk/lib/CodeGen/CodeGenFunction.cpp
@@ -103,6 +103,9 @@
   if (CGM.getCodeGenOpts().ReciprocalMath) {
     FMF.setAllowReciprocal();
   }
+  if (CGM.getCodeGenOpts().Reassociate) {
+    FMF.setAllowReassoc();
+  }
   Builder.setFastMathFlags(FMF);
 }
 
Index: cfe/trunk/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- cfe/trunk/lib/Driver/ToolChains/Clang.cpp
+++ cfe/trunk/lib/Driver/ToolChains/Clang.cpp
@@ -2170,6 +2170,9 @@
   if (!SignedZeros)
     CmdArgs.push_back("-fno-signed-zeros");
 
+  if (AssociativeMath && !SignedZeros && !TrappingMath)
+    CmdArgs.push_back("-mreassociate");
+
   if (ReciprocalMath)
     CmdArgs.push_back("-freciprocal-math");
 
Index: cfe/trunk/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- cfe/trunk/lib/Frontend/CompilerInvocation.cpp
+++ cfe/trunk/lib/Frontend/CompilerInvocation.cpp
@@ -639,6 +639,7 @@
                         Args.hasArg(OPT_cl_no_signed_zeros) ||
                         Args.hasArg(OPT_cl_unsafe_math_optimizations) ||
                         Args.hasArg(OPT_cl_fast_relaxed_math));
+  Opts.Reassociate = Args.hasArg(OPT_mreassociate);
   Opts.FlushDenorm = Args.hasArg(OPT_cl_denorms_are_zero);
   Opts.CorrectlyRoundedDivSqrt =
       Args.hasArg(OPT_cl_fp32_correctly_rounded_divide_sqrt);
Index: cfe/trunk/test/CodeGen/finite-math.c
===================================================================
--- cfe/trunk/test/CodeGen/finite-math.c
+++ cfe/trunk/test/CodeGen/finite-math.c
@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -ffinite-math-only -emit-llvm -o - %s | FileCheck %s -check-prefix=CHECK -check-prefix=FINITE
 // RUN: %clang_cc1 -fno-signed-zeros -emit-llvm -o - %s | FileCheck %s -check-prefix=CHECK  -check-prefix=NSZ
 // RUN: %clang_cc1 -freciprocal-math -emit-llvm -o - %s | FileCheck %s -check-prefix=CHECK  -check-prefix=RECIP
+// RUN: %clang_cc1 -mreassociate -emit-llvm -o - %s | FileCheck %s -check-prefix=CHECK  -check-prefix=REASSOC
 
 float f0, f1, f2;
 
@@ -10,6 +11,7 @@
   // FINITE: fadd nnan ninf
   // NSZ: fadd nsz
   // RECIP: fadd arcp
+  // REASSOC: fadd reassoc
   f0 = f1 + f2;
 
   // CHECK: ret
Index: cfe/trunk/test/Driver/fast-math.c
===================================================================
--- cfe/trunk/test/Driver/fast-math.c
+++ cfe/trunk/test/Driver/fast-math.c
@@ -121,18 +121,23 @@
 // RUN:   | FileCheck --check-prefix=CHECK-UNSAFE-MATH %s
 // CHECK-UNSAFE-MATH: "-cc1"
 // CHECK-UNSAFE-MATH: "-menable-unsafe-fp-math"
+// CHECK-UNSAFE-MATH: "-mreassociate"
 //
 // RUN: %clang -### -fno-fast-math -fno-math-errno -fassociative-math -freciprocal-math \
 // RUN:     -fno-signed-zeros -fno-trapping-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH-UNSAFE-MATH %s
 // CHECK-NO-FAST-MATH-UNSAFE-MATH: "-cc1"
 // CHECK-NO-FAST-MATH-UNSAFE-MATH: "-menable-unsafe-fp-math"
-//
+// CHECK-NO-FAST-MATH-UNSAFE-MATH: "-mreassociate"
+
+// The 2nd -fno-fast-math overrides -fassociative-math.
+
 // RUN: %clang -### -fno-fast-math -fno-math-errno -fassociative-math -freciprocal-math \
 // RUN:     -fno-fast-math -fno-signed-zeros -fno-trapping-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-UNSAFE-MATH-NO-FAST-MATH %s
 // CHECK-UNSAFE-MATH-NO-FAST-MATH: "-cc1"
 // CHECK-UNSAFE-MATH-NO-FAST-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-UNSAFE-MATH-NO-FAST-MATH-NOT: "-mreassociate"
 //
 // Check that various umbrella flags also enable these frontend options.
 // RUN: %clang -### -ffast-math -c %s 2>&1 \
@@ -151,7 +156,7 @@
 // One umbrella flag is *really* weird and also changes the semantics of the
 // program by adding a special preprocessor macro. Check that the frontend flag
 // modeling this semantic change is provided. Also check that the flag is not
-// present if any of the optimization is disabled.
+// present if any of the optimizations are disabled.
 // RUN: %clang -### -ffast-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FAST-MATH %s
 // RUN: %clang -### -fno-fast-math -ffast-math -c %s 2>&1 \
@@ -175,8 +180,11 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH %s
 // RUN: %clang -### -ffast-math -fmath-errno -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH %s
+// RUN: %clang -### -ffast-math -fno-associative-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH --check-prefix=CHECK-ASSOC-MATH %s
 // CHECK-NO-FAST-MATH: "-cc1"
 // CHECK-NO-FAST-MATH-NOT: "-ffast-math"
+// CHECK-ASSOC-MATH-NOT: "-mreassociate"
 //
 // Check various means of disabling these flags, including disabling them after
 // they've been enabled via an umbrella flag.
@@ -209,21 +217,16 @@
 // CHECK-NO-NO-NANS-NOT: "-menable-no-nans"
 // CHECK-NO-NO-NANS-NOT: "-ffinite-math-only"
 // CHECK-NO-NO-NANS: "-o"
-//
+
+// A later inverted option overrides an earlier option.
+
 // RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
 // RUN:     -fno-trapping-math -fno-associative-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
-// RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
-// RUN:     -fno-trapping-math -fno-reciprocal-math -c %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
-// RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
-// RUN:     -fno-trapping-math -fsigned-zeros -c %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
-// RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
-// RUN:     -fno-trapping-math -ftrapping-math -c %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
+
 // RUN: %clang -### -funsafe-math-optimizations -fno-associative-math -c %s \
 // RUN:   2>&1 | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
+
 // RUN: %clang -### -funsafe-math-optimizations -fno-reciprocal-math -c %s \
 // RUN:   2>&1 | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
 // RUN: %clang -### -funsafe-math-optimizations -fsigned-zeros -c %s 2>&1 \
@@ -235,6 +238,7 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
 // RUN: %clang -### -ffast-math -fno-associative-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
+
 // RUN: %clang -### -ffast-math -fno-reciprocal-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
 // RUN: %clang -### -ffast-math -fsigned-zeros -c %s 2>&1 \
@@ -243,10 +247,43 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
 // RUN: %clang -### -ffast-math -fno-unsafe-math-optimizations -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
+
 // CHECK-NO-UNSAFE-MATH: "-cc1"
 // CHECK-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-NO_UNSAFE-MATH-NOT: "-mreassociate"
 // CHECK-NO-UNSAFE-MATH: "-o"
-//
+
+
+// Reassociate is allowed because it does not require reciprocal-math.
+
+// RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
+// RUN:     -fno-trapping-math -fno-reciprocal-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-REASSOC-NO-UNSAFE-MATH %s
+
+// CHECK-REASSOC-NO-UNSAFE-MATH: "-cc1"
+// CHECK-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-REASSOC-NO_UNSAFE-MATH: "-mreassociate"
+// CHECK-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-REASSOC-NO-UNSAFE-MATH: "-o"
+
+
+// In these runs, reassociate is not allowed because both no-signed-zeros and no-trapping-math are required.
+
+// RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
+// RUN:     -fno-trapping-math -fsigned-zeros -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-REASSOC-NO-UNSAFE-MATH %s
+
+// RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
+// RUN:     -fno-trapping-math -ftrapping-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-REASSOC-NO-UNSAFE-MATH %s
+
+// CHECK-NO-REASSOC-NO-UNSAFE-MATH: "-cc1"
+// CHECK-NO-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-NO-REASSOC-NO_UNSAFE-MATH-NOT: "-mreassociate"
+// CHECK-NO-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-NO-REASSOC-NO-UNSAFE-MATH: "-o"
+
+
 // RUN: %clang -### -ftrapping-math -fno-trapping-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-TRAPPING-MATH %s
 // CHECK-NO-TRAPPING-MATH: "-fno-trapping-math"