9 files changed, 49 insertions, 43 deletions
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index b6672bdbfdd..ba7898ba33b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -89,14 +89,13 @@ Non-comprehensive list of changes in this release
 New Compiler Flags
 ------------------
 
-- :option:`-ffp-cast-overflow-workaround` and
-  :option:`-fno-fp-cast-overflow-workaround`
-  enable (disable) a workaround for code that casts floating-point values to
-  integers and back to floating-point. If the floating-point value is not
-  representable in the intermediate integer type, the code is incorrect
-  according to the language standard. This flag will attempt to generate code
-  as if the result of an overflowing conversion matches the overflowing behavior
-  of a target's native float-to-int conversion instructions.
+- :option:`-fstrict-float-cast-overflow` and
+  :option:`-fno-strict-float-cast-overflow` -
+   When a floating-point value is not representable in a destination integer
+   type, the code has undefined behavior according to the language standard.
+   By default, Clang will not guarantee any particular result in that case.
+   With the 'no-strict' option, Clang attempts to match the overflowing behavior
+   of the target's native float-to-int conversion instructions.
 
 - ...
 
diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index 7425d2ad974..729adfdd397 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -1255,15 +1255,13 @@ are listed below.
    flushed-to-zero number is preserved in the sign of 0, denormals are
    flushed to positive zero, respectively.
 
-.. option:: -f[no-]fp-cast-overflow-workaround
-
-   Enable a workaround for code that casts floating-point values to 
-   integers and back to floating-point. If the floating-point value 
-   is not representable in the intermediate integer type, the code is
-   incorrect according to the language standard. This flag will attempt 
-   to generate code as if the result of an overflowing conversion matches
-   the overflowing behavior of a target's native float-to-int conversion
-   instructions.
+.. option:: -f[no-]strict-float-cast-overflow
+
+   When a floating-point value is not representable in a destination integer 
+   type, the code has undefined behavior according to the language standard.
+   By default, Clang will not guarantee any particular result in that case.
+   With the 'no-strict' option, Clang attempts to match the overflowing behavior
+   of the target's native float-to-int conversion instructions.
 
 .. option:: -fwhole-program-vtables
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index f18a3b17463..3a5d58a8ee7 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1029,10 +1029,12 @@ def ffp_contract : Joined<["-"], "ffp-contract=">, Group<f_Group>,
   Flags<[CC1Option]>, HelpText<"Form fused FP ops (e.g. FMAs): fast (everywhere)"
   " | on (according to FP_CONTRACT pragma, default) | off (never fuse)">, Values<"fast,on,off">;
 
-def ffp_cast_overflow_workaround : Flag<["-"],
-  "ffp-cast-overflow-workaround">, Group<f_Group>, Flags<[CC1Option]>;
-def fno_fp_cast_overflow_workaround : Flag<["-"],
-  "fno-fp-cast-overflow-workaround">, Group<f_Group>, Flags<[CC1Option]>;
+def fstrict_float_cast_overflow : Flag<["-"],
+  "fstrict-float-cast-overflow">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Assume that overflowing float-to-int casts are undefined (default)">;
+def fno_strict_float_cast_overflow : Flag<["-"],
+  "fno-strict-float-cast-overflow">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Relax language rules and try to match the behavior of the target's native float-to-int conversion instructions">;
 
 def ffor_scope : Flag<["-"], "ffor-scope">, Group<f_Group>;
 def fno_for_scope : Flag<["-"], "fno-for-scope">, Group<f_Group>;
diff --git a/clang/include/clang/Frontend/CodeGenOptions.def b/clang/include/clang/Frontend/CodeGenOptions.def
index 1747aa7287f..52e10b3f761 100644
--- a/clang/include/clang/Frontend/CodeGenOptions.def
+++ b/clang/include/clang/Frontend/CodeGenOptions.def
@@ -137,10 +137,10 @@ CODEGENOPT(NoNaNsFPMath      , 1, 0) ///< Assume FP arguments, results not NaN.
 CODEGENOPT(FlushDenorm       , 1, 0) ///< Allow FP denorm numbers to be flushed to zero
 CODEGENOPT(CorrectlyRoundedDivSqrt, 1, 0) ///< -cl-fp32-correctly-rounded-divide-sqrt
 
-/// Disable a float-to-int-to-float cast optimization. This attempts to generate
-/// code as if the result of an overflowing conversion matches the overflowing
-/// behavior of a target's native float-to-int conversion instructions.
-CODEGENOPT(FPCastOverflowWorkaround, 1, 0)
+/// When false, this attempts to generate code as if the result of an
+/// overflowing conversion matches the overflowing behavior of a target's native
+/// float-to-int conversion instructions.
+CODEGENOPT(StrictFloatCastOverflow, 1, 1)
 
 CODEGENOPT(UniformWGSize     , 1, 0) ///< -cl-uniform-work-group-size
 CODEGENOPT(NoZeroInitializedInBSS , 1, 0) ///< -fno-zero-initialized-in-bss.
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index da2ff14b598..89f86ca99ee 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1727,8 +1727,10 @@ void CodeGenModule::ConstructDefaultFnAttrList(StringRef Name, bool HasOptnone,
     FuncAttrs.addAttribute("no-trapping-math",
                            llvm::toStringRef(CodeGenOpts.NoTrappingMath));
 
-    if (CodeGenOpts.FPCastOverflowWorkaround)
-      FuncAttrs.addAttribute("fp-cast-overflow-workaround", "true");
+    // Strict (compliant) code is the default, so only add this attribute to
+    // indicate that we are trying to workaround a problem case.
+    if (!CodeGenOpts.StrictFloatCastOverflow)
+      FuncAttrs.addAttribute("strict-float-cast-overflow", "false");
 
     // TODO: Are these all needed?
     // unsafe/inf/nan/nsz are handled by instruction-level FastMathFlags.
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 3dc657e8851..331b4beaa6b 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2243,9 +2243,9 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
   }
 
   // Disable a codegen optimization for floating-point casts.
-  if (Args.hasFlag(options::OPT_ffp_cast_overflow_workaround,
-                   options::OPT_fno_fp_cast_overflow_workaround, false))
-    CmdArgs.push_back("-ffp-cast-overflow-workaround");
+  if (Args.hasFlag(options::OPT_fno_strict_float_cast_overflow,
+                   options::OPT_fstrict_float_cast_overflow, false))
+    CmdArgs.push_back("-fno-strict-float-cast-overflow");
 }
 
 static void RenderAnalyzerOptions(const ArgList &Args, ArgStringList &CmdArgs,
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 9ef4ad77558..44f29ba3b10 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -699,7 +699,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.Reciprocals = Args.getAllArgValues(OPT_mrecip_EQ);
   Opts.ReciprocalMath = Args.hasArg(OPT_freciprocal_math);
   Opts.NoTrappingMath = Args.hasArg(OPT_fno_trapping_math);
-  Opts.FPCastOverflowWorkaround = Args.hasArg(OPT_ffp_cast_overflow_workaround);
+  Opts.StrictFloatCastOverflow =
+      !Args.hasArg(OPT_fno_strict_float_cast_overflow);
 
   Opts.NoZeroInitializedInBSS = Args.hasArg(OPT_mno_zero_initialized_in_bss);
   Opts.NumRegisterParameters = getLastArgIntValue(Args, OPT_mregparm, 0, Diags);
diff --git a/clang/test/CodeGen/no-junk-ftrunc.c b/clang/test/CodeGen/no-junk-ftrunc.c
index ff3f640e837..a645d968866 100644
--- a/clang/test/CodeGen/no-junk-ftrunc.c
+++ b/clang/test/CodeGen/no-junk-ftrunc.c
@@ -1,12 +1,16 @@
-// RUN: %clang_cc1 -S -ffp-cast-overflow-workaround %s -emit-llvm -o - | FileCheck %s
-// CHECK-LABEL: main
-// CHECK: attributes #0 = {{.*}}"fp-cast-overflow-workaround"="true"{{.*}}
+// RUN: %clang_cc1 -S -fno-strict-float-cast-overflow %s -emit-llvm -o - | FileCheck %s --check-prefix=NOSTRICT
+// NOSTRICT-LABEL: main
+// NOSTRICT: attributes #0 = {{.*}}"strict-float-cast-overflow"="false"{{.*}}
 
 // The workaround attribute is not applied by default.
 
+// RUN: %clang_cc1 -S %s -fstrict-float-cast-overflow -emit-llvm -o - | FileCheck %s --check-prefix=STRICT
+// STRICT-LABEL: main
+// STRICT-NOT: strict-float-cast-overflow
+
 // RUN: %clang_cc1 -S %s -emit-llvm -o - | FileCheck %s --check-prefix=DEFAULT
 // DEFAULT-LABEL: main
-// DEFAULT-NOT: fp-cast-overflow-workaround
+// DEFAULT-NOT: strict-float-cast-overflow
 
 int main() {
   return 0;
diff --git a/clang/test/Driver/fast-math.c b/clang/test/Driver/fast-math.c
index e1e07f37742..57e5d2c7157 100644
--- a/clang/test/Driver/fast-math.c
+++ b/clang/test/Driver/fast-math.c
@@ -289,25 +289,25 @@
 // CHECK-NO-TRAPPING-MATH: "-fno-trapping-math"
 
 // This isn't fast-math, but the option is handled in the same place as other FP params.
-// Last option wins, and the flag is *not* passed by default. 
+// Last option wins, and strict behavior is assumed by default. 
 
-// RUN: %clang -### -ffp-cast-overflow-workaround -c %s 2>&1 \
+// RUN: %clang -### -fno-strict-float-cast-overflow -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FPOV-WORKAROUND %s
 // CHECK-FPOV-WORKAROUND: "-cc1"
-// CHECK-FPOV-WORKAROUND: "-ffp-cast-overflow-workaround"
+// CHECK-FPOV-WORKAROUND: "-fno-strict-float-cast-overflow"
 
 // RUN: %clang -### -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FPOV-WORKAROUND-DEFAULT %s
 // CHECK-FPOV-WORKAROUND-DEFAULT: "-cc1"
-// CHECK-FPOV-WORKAROUND-DEFAULT-NOT: "-ffp-cast-overflow-workaround"
+// CHECK-FPOV-WORKAROUND-DEFAULT-NOT: "strict-float-cast-overflow"
 
-// RUN: %clang -### -fno-fp-cast-overflow-workaround -c %s 2>&1 \
+// RUN: %clang -### -fstrict-float-cast-overflow -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FPOV-WORKAROUND %s
 // CHECK-NO-FPOV-WORKAROUND: "-cc1"
-// CHECK-NO-FPOV-WORKAROUND-NOT: "-ffp-cast-overflow-workaround"
+// CHECK-NO-FPOV-WORKAROUND-NOT: "strict-float-cast-overflow"
 
-// RUN: %clang -### -ffp-cast-overflow-workaround -fno-fp-cast-overflow-workaround -c %s 2>&1 \
+// RUN: %clang -### -fno-strict-float-cast-overflow -fstrict-float-cast-overflow -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FPOV-WORKAROUND-OVERRIDE %s
 // CHECK-NO-FPOV-WORKAROUND-OVERRIDE: "-cc1"
-// CHECK-NO-FPOV-WORKAROUND-OVERRIDE-NOT: "-ffp-cast-overflow-workaround"
+// CHECK-NO-FPOV-WORKAROUND-OVERRIDE-NOT: "strict-float-cast-overflow"