Revert "Revert "Change clang option -ffp-model=precise to select ffp-contract=on""

This reverts commit 99c5bcbce8.
Change clang option -ffp-model=precise to select ffp-contract=on
Including some small touch-ups to the original commit

Reviewers: rjmccall, Andy Kaylor

Differential Revision: https://reviews.llvm.org/D74436

clang/docs/UsersManual.rst

@@ -1190,8 +1190,50 @@ installed.
 Controlling Floating Point Behavior
 -----------------------------------
 
-Clang provides a number of ways to control floating point behavior. The options
-are listed below.
+Clang provides a number of ways to control floating point behavior, including
+with command line options and source pragmas. This section
+describes the various floating point semantic modes and the corresponding options.
+
+.. csv-table:: Floating Point Semantic Modes
+  :header: "Mode", "Values"
+  :widths: 15, 30, 30
+
+  "except_behavior", "{ignore, strict, may_trap}", "ffp-exception-behavior"
+  "fenv_access", "{off, on}", "(none)"
+  "rounding_mode", "{dynamic, tonearest, downward, upward, towardzero}", "frounding-math"
+  "contract", "{on, off, fast}", "ffp-contract"
+  "denormal_fp_math", "{IEEE, PreserveSign, PositiveZero}", "fdenormal-fp-math"
+  "denormal_fp32_math", "{IEEE, PreserveSign, PositiveZero}", "fdenormal-fp-math-fp32"
+  "support_math_errno", "{on, off}", "fmath-errno"
+  "no_honor_nans", "{on, off}", "fhonor-nans"
+  "no_honor_infinities", "{on, off}", "fhonor-infinities"
+  "no_signed_zeros", "{on, off}", "fsigned-zeros"
+  "allow_reciprocal", "{on, off}", "freciprocal-math"
+  "allow_approximate_fns", "{on, off}", "(none)"
+  "allow_reassociation", "{on, off}", "fassociative-math"
+
+
+This table describes the option settings that correspond to the three
+floating point semantic models: precise (the default), strict, and fast.
+
+
+.. csv-table:: Floating Point Models
+  :header: "Mode", "Precise", "Strict", "Fast"
+  :widths: 25, 15, 15, 15
+
+  "except_behavior", "ignore", "strict", "ignore"
+  "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"
+  "support_math_errno", "on", "on", "off"
+  "no_honor_nans", "off", "off", "on"
+  "no_honor_infinities", "off", "off", "on"
+  "no_signed_zeros", "off", "off", "on"
+  "allow_reciprocal", "off", "off", "on"
+  "allow_approximate_fns", "off", "off", "on"
+  "allow_reassociation", "off", "off", "on"
 
 .. option:: -ffast-math
 
@@ -1385,7 +1427,7 @@ Note that floating-point operations performed as part of constant initialization
    and ``fast``.
    Details:
 
-   * ``precise`` Disables optimizations that are not value-safe on floating-point data, although FP contraction (FMA) is enabled (``-ffp-contract=fast``).  This is the default behavior.
+   * ``precise`` Disables optimizations that are not value-safe on floating-point data, although FP contraction (FMA) is enabled (``-ffp-contract=on``).  This is the default behavior.
    * ``strict`` Enables ``-frounding-math`` and ``-ffp-exception-behavior=strict``, and disables contractions (FMA).  All of the ``-ffast-math`` enablements are disabled.
    * ``fast`` Behaves identically to specifying both ``-ffast-math`` and ``ffp-contract=fast``
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -2525,10 +2525,9 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
 
   llvm::DenormalMode DenormalFPMath = DefaultDenormalFPMath;
   llvm::DenormalMode DenormalFP32Math = DefaultDenormalFP32Math;
-  StringRef FPContract = "";
+  StringRef FPContract = "on";
   bool StrictFPModel = false;
 
-
   if (const Arg *A = Args.getLastArg(options::OPT_flimited_precision_EQ)) {
     CmdArgs.push_back("-mlimit-float-precision");
     CmdArgs.push_back(A->getValue());
@@ -2551,7 +2550,6 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       SignedZeros = true;
       // -fno_fast_math restores default denormal and fpcontract handling
       DenormalFPMath = DefaultDenormalFPMath;
-      FPContract = "";
       StringRef Val = A->getValue();
       if (OFastEnabled && !Val.equals("fast")) {
           // Only -ffp-model=fast is compatible with OFast, ignore.
@@ -2565,12 +2563,10 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       // ffp-model= is a Driver option, it is entirely rewritten into more
       // granular options before being passed into cc1.
       // Use the gcc option in the switch below.
-      if (!FPModel.empty() && !FPModel.equals(Val)) {
+      if (!FPModel.empty() && !FPModel.equals(Val))
         D.Diag(clang::diag::warn_drv_overriding_flag_option)
           << Args.MakeArgString("-ffp-model=" + FPModel)
           << Args.MakeArgString("-ffp-model=" + Val);
-        FPContract = "";
-      }
       if (Val.equals("fast")) {
         optID = options::OPT_ffast_math;
         FPModel = Val;
@@ -2578,13 +2574,14 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       } else if (Val.equals("precise")) {
         optID = options::OPT_ffp_contract;
         FPModel = Val;
-        FPContract = "fast";
+        FPContract = "on";
         PreciseFPModel = true;
       } else if (Val.equals("strict")) {
         StrictFPModel = true;
         optID = options::OPT_frounding_math;
         FPExceptionBehavior = "strict";
         FPModel = Val;
+        FPContract = "off";
         TrappingMath = true;
       } else
         D.Diag(diag::err_drv_unsupported_option_argument)
@@ -2663,9 +2660,11 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
     case options::OPT_ffp_contract: {
       StringRef Val = A->getValue();
       if (PreciseFPModel) {
-        // -ffp-model=precise enables ffp-contract=fast as a side effect
-        // the FPContract value has already been set to a string literal
-        // and the Val string isn't a pertinent value.
+        // When -ffp-model=precise is seen on the command line,
+        // the boolean PreciseFPModel is set to true which indicates
+        // "the current option is actually PreciseFPModel". The optID
+        // is changed to OPT_ffp_contract and FPContract is set to "on".
+        // the argument Val string is "precise": it shouldn't be checked.
         ;
       } else if (Val.equals("fast") || Val.equals("on") || Val.equals("off"))
         FPContract = Val;
@@ -2762,7 +2761,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       // -fno_fast_math restores default denormal and fpcontract handling
       DenormalFPMath = DefaultDenormalFPMath;
       DenormalFP32Math = DefaultDenormalFP32Math;
-      FPContract = "";
+      FPContract = "on";
       break;
     }
     if (StrictFPModel) {
@@ -2773,7 +2772,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
         !AssociativeMath && !ReciprocalMath &&
         SignedZeros && TrappingMath && RoundingFPMath &&
         DenormalFPMath != llvm::DenormalMode::getIEEE() &&
-        FPContract.empty())
+        FPContract.equals("off"))
         // OK: Current Arg doesn't conflict with -ffp-model=strict
         ;
       else {

clang/test/CodeGen/ppc-emmintrin.c

@@ -2,9 +2,9 @@
 // REQUIRES: powerpc-registered-target
 
 // RUN: %clang -S -emit-llvm -target powerpc64-unknown-linux-gnu -mcpu=pwr8 -ffreestanding -DNO_WARN_X86_INTRINSICS %s \
-// RUN:  -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN:  -ffp-contract=off -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-BE
 // RUN: %clang -S -emit-llvm -target powerpc64le-unknown-linux-gnu -mcpu=pwr8 -ffreestanding -DNO_WARN_X86_INTRINSICS %s \
-// RUN:   -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-LE
+// RUN:   -ffp-contract=off -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-LE
 
 // CHECK-BE-DAG: @_mm_movemask_pd.perm_mask = internal constant <4 x i32> <i32 -2139062144, i32 -2139062144, i32 -2139062144, i32 -2139078656>, align 16
 // CHECK-BE-DAG: @_mm_shuffle_epi32.permute_selectors = internal constant [4 x i32] [i32 66051, i32 67438087, i32 134810123, i32 202182159], align 4

clang/test/CodeGen/ppc-xmmintrin.c

@@ -2,9 +2,9 @@
 // REQUIRES: powerpc-registered-target
 
 // RUN: %clang -S -emit-llvm -target powerpc64-unknown-linux-gnu -mcpu=pwr8 -ffreestanding -DNO_WARN_X86_INTRINSICS %s \
-// RUN:   -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN:   -ffp-contract=off -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-BE
 // RUN: %clang -S -emit-llvm -target powerpc64le-unknown-linux-gnu -mcpu=pwr8 -ffreestanding -DNO_WARN_X86_INTRINSICS %s \
-// RUN:   -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-LE
+// RUN:   -ffp-contract=off -fno-discard-value-names -mllvm -disable-llvm-optzns -o - | llvm-cxxfilt -n | FileCheck %s --check-prefixes=CHECK,CHECK-LE
 
 #include <xmmintrin.h>
 

clang/test/Driver/fp-model.c

@@ -27,9 +27,9 @@
 // RUN:   | FileCheck --check-prefix=WARN5 %s
 // WARN5: warning: overriding '-ffp-model=strict' option with '-ffp-contract=fast' [-Woverriding-t-option]
 
-// RUN: %clang -### -ffp-model=strict -ffp-contract=off -c %s 2>&1 \
+// RUN: %clang -### -ffp-model=strict -ffp-contract=fast -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=WARN6 %s
-// WARN6: warning: overriding '-ffp-model=strict' option with '-ffp-contract=off' [-Woverriding-t-option]
+// WARN6: warning: overriding '-ffp-model=strict' option with '-ffp-contract=fast' [-Woverriding-t-option]
 
 // RUN: %clang -### -ffp-model=strict -ffp-contract=on -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=WARN7 %s
@@ -100,13 +100,14 @@
 // RUN: %clang -### -nostdinc -ffp-model=precise -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FPM-PRECISE %s
 // CHECK-FPM-PRECISE: "-cc1"
-// CHECK-FPM-PRECISE: "-ffp-contract=fast"
+// CHECK-FPM-PRECISE: "-ffp-contract=on"
 // CHECK-FPM-PRECISE: "-fno-rounding-math"
 
 // RUN: %clang -### -nostdinc -ffp-model=strict -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FPM-STRICT %s
 // CHECK-FPM-STRICT: "-cc1"
 // CHECK-FPM-STRICT: "-ftrapping-math"
+// CHECK-FPM-STRICT: "-ffp-contract=off"
 // CHECK-FPM-STRICT: "-frounding-math"
 // CHECK-FPM-STRICT: "-ffp-exception-behavior=strict"