Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -1359,8 +1359,8 @@
   "fenv_access", "off", "on", "off"
   "rounding_mode", "tonearest", "dynamic", "tonearest"
   "contract", "on", "off", "fast"
-  "denormal_fp_math", "IEEE", "IEEE", "PreserveSign"
-  "denormal_fp32_math", "IEEE","IEEE", "PreserveSign"
+  "denormal_fp_math", "IEEE", "IEEE", "IEEE"
+  "denormal_fp32_math", "IEEE","IEEE", "IEEE"
   "support_math_errno", "on", "on", "off"
   "no_honor_nans", "off", "off", "on"
   "no_honor_infinities", "off", "off", "on"
@@ -1408,6 +1408,60 @@
 
    * ``-ffp-contract=fast``
 
+   Note: ``-ffast-math`` causes ``crtfastmath.o`` to be linked with code.
+
+.. option:: -fno-fast-math
+
+   Disable fast-math mode.  This options disables unsafe floating-point
+   optimizations by preventing the compiler from making any tranformations that
+   could affect the results.
+
+   This option implies:
+
+   * ``-fhonor-infinities``
+
+   * ``-fhonor-nans``
+
+   * ``-fmath-errno``
+
+   * ``-fno-finite-math-only``
+
+   * ``-fno-associative-math``
+
+   * ``-fno-reciprocal-math``
+
+   * ``-fsigned-zeros``
+
+   * ``-fno-trapping-math``
+
+   * ``-ffp-contract=on``
+
+   * ``-fdenormal-fp-math=ieee``
+
+   There is ambiguity about how ``-ffp-contract``, ``-ffast-math``,
+   and ``-fno-fast-math`` behave in combination. To keep the value of
+   ``-ffp-contract`` consistent, we define this set of rules:
+
+   * ``-ffast-math`` sets ``ffp-contract`` to ``fast``.
+
+   * ``-fno-fast-math`` sets ``-ffp-contract`` to ``on`` (``fast`` for CUDA and
+     HIP).
+
+   * If ``-ffast-math`` and ``-ffp-contract`` are both seen, but
+     ``-ffast-math`` is not followed by ``-fno-fast-math``, ``ffp-contract``
+     will be given the value of whichever option was last seen.
+
+   * If ``-fno-fast-math`` is seen and ``-ffp-contract`` has been seen at least
+     once, the ``ffp-contract`` will get the value of the last seen value of
+     ``-ffp-contract``.
+
+   * If ``-fno-fast-math`` is seen and ``-ffp-contract`` has not been seen, the
+     ``-ffp-contract`` setting is determined by the default value of
+     ``-ffp-contract`.
+
+   Note: ``-fno-fast-math`` implies ``-fdenormal-fp-math=ieee``.
+   ``-fno-fast-math`` causes ``crtfastmath.o`` to not be linked with code.
+
 .. option:: -fdenormal-fp-math=<value>
 
    Select which denormal numbers the code is permitted to require.
@@ -1632,6 +1686,15 @@
    has no effect because the optimizer is prohibited from making unsafe
    transformations.
 
+.. _crtfastmath.o:
+
+A note about ``crtfastmath.o``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+``-ffast-math`` and ``-funsafe-math-optimizations`` cause ``crtfastmath.o`` to be
+linked,  which adds a static constructor that sets the FTZ/DAZ bits in MXCSR,
+affecting not only the current compilation unit but all static and shared
+libraries included in the program.
+
 .. _FLT_EVAL_METHOD:
 
 A note about ``__FLT_EVAL_METHOD__``
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -2786,6 +2786,8 @@
   // CUDA and HIP don't rely on the frontend to pass an ffp-contract option.
   // If one wasn't given by the user, don't pass it here.
   StringRef FPContract;
+  StringRef LastSeenFfpContractOption;
+  bool SeenFfastMathOption = false;
   if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
       !JA.isOffloading(Action::OFK_HIP))
     FPContract = "on";
@@ -2936,9 +2938,10 @@
         // -ffp-model=precise sets PreciseFPModel to on and Val to
         // "precise". FPContract is set.
         ;
-      } else if (Val.equals("fast") || Val.equals("on") || Val.equals("off"))
+      } else if (Val.equals("fast") || Val.equals("on") || Val.equals("off")) {
         FPContract = Val;
-      else
+        LastSeenFfpContractOption = Val;
+      } else
         D.Diag(diag::err_drv_unsupported_option_argument)
            << A->getOption().getName() << Val;
       break;
@@ -3031,6 +3034,7 @@
       RoundingFPMath = false;
       // If fast-math is set then set the fp-contract mode to fast.
       FPContract = "fast";
+      SeenFfastMathOption = true;
       break;
     case options::OPT_fno_fast_math:
       HonorINFs = true;
@@ -3047,13 +3051,12 @@
       DenormalFPMath = DefaultDenormalFPMath;
       DenormalFP32Math = llvm::DenormalMode::getIEEE();
       if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
-          !JA.isOffloading(Action::OFK_HIP))
-        if (FPContract == "fast") {
+          !JA.isOffloading(Action::OFK_HIP)) {
+        if (LastSeenFfpContractOption != "") {
+          FPContract = LastSeenFfpContractOption;
+        } else if (SeenFfastMathOption)
           FPContract = "on";
-          D.Diag(clang::diag::warn_drv_overriding_flag_option)
-              << "-ffp-contract=fast"
-              << "-ffp-contract=on";
-        }
+      }
       break;
     }
     if (StrictFPModel) {
Index: clang/test/CodeGen/ffp-contract-option.c
===================================================================
--- clang/test/CodeGen/ffp-contract-option.c
+++ clang/test/CodeGen/ffp-contract-option.c
@@ -35,7 +35,7 @@
 // RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
 
 // RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-contract=fast -fno-fast-math \
-// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
+// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-CONTRACTFAST
 
 // RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-contract=on -fno-fast-math \
 // RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
Index: clang/test/Driver/fp-contract.c
===================================================================
--- /dev/null
+++ clang/test/Driver/fp-contract.c
@@ -0,0 +1,114 @@
+// Test that -ffp-contract is set to the right value when combined with
+// the options -ffast-math and -fno-fast-math.
+
+// RUN: %clang -### -ffast-math -c %s 2>&1  \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+// CHECK-FPC-FAST:     "-ffp-contract=fast"
+
+// RUN: %clang -### -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=on -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+// CHECK-FPC-ON:       "-ffp-contract=on"
+
+// RUN: %clang -### -ffast-math -ffp-contract=off -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-OFF %s
+// CHECK-FPC-OFF:      "-ffp-contract=off"
+
+// RUN: %clang -### -ffast-math -ffp-contract=fast -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffp-contract=fast -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+// RUN: %clang -### -ffp-contract=on -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+// RUN: %clang -### -ffp-contract=off -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffp-contract=fast -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+// RUN: %clang -### -ffp-contract=on -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+// RUN: %clang -### -ffp-contract=off -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-OFF %s
+
+
+// RUN: %clang -### -ffast-math -ffp-contract=fast -ffp-contract=on -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=on -ffp-contract=off -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-OFF %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=on -ffp-contract=fast -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=off -ffp-contract=on -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=off -ffp-contract=fast \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=on -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=off -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-OFF %s
+
+// RUN: %clang -### -ffast-math -ffp-contract=fast -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffast-math -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -fno-fast-math -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -fno-fast-math -ffp-contract=on -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -fno-fast-math -ffp-contract=off -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-OFF %s
+
+// RUN: %clang -### -fno-fast-math -ffp-contract=fast -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffp-contract=fast -fno-fast-math -ffp-contract=on \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -ffp-contract=fast -fno-fast-math -ffp-contract=off \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-OFF %s
+
+// RUN: %clang -### -ffp-contract=off -fno-fast-math -ffp-contract=fast \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffp-contract=off -fno-fast-math -ffp-contract=on \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -ffp-contract=on -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffp-contract=off -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffp-contract=fast -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -ffp-contract=on -ffast-math -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -ffp-contract=off -ffast-math -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-OFF %s
+
+// RUN: %clang -### -ffp-contract=fast -ffast-math -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -fno-fast-math -ffast-math -ffp-contract=fast \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-FAST %s
+
+// RUN: %clang -### -fno-fast-math -ffast-math -ffp-contract=on \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-ON %s
+
+// RUN: %clang -### -fno-fast-math -ffast-math -ffp-contract=off \
+// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-OFF %s
+