[Driver, CodeGen] rename options to disable an FP cast optimization

As suggested in the post-commit thread for rL331056, we should match these 
clang options with the established vocabulary of the corresponding sanitizer
option. Also, the use of 'strict' is well-known for these kinds of knobs, 
and we can improve the descriptive text in the docs.

So this intends to match the logic of D46135 but only change the words.
Matching LLVM commit to match this spelling of the attribute to follow shortly.

Differential Revision: https://reviews.llvm.org/D46236

llvm-svn: 331209

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.
 
 - ...
 

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
+.. option:: -f[no-]strict-float-cast-overflow
 
-   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.
+   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
 

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>;

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.

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.

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,

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);

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;

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"