[clang] [Driver] Introduce ffp-model=aggressive (PR #100453)
Andy Kaylor via cfe-commits
cfe-commits at lists.llvm.org
Wed Jul 24 12:47:16 PDT 2024
https://github.com/andykaylor created https://github.com/llvm/llvm-project/pull/100453
This change modifies -ffp-model=fast to select options that more closely
match -funsafe-math-optimizations, and introduces a new model,
-ffp-model=aggressive which matches the existing behavior (except for a
minor change in the fp-contract behavior).
The primary motivation for this change is to make -ffp-model=fast more
user friendly, particularly in light of LLVM's aggressive optimizations
when -fno-honor-nans and -fno-honor-infinites are used.
This was previously proposed here:
https://discourse.llvm.org/t/making-ffp-model-fast-more-user-friendly/78402
>From cf7bf482e7ce11f0ca1add4b0bb62a327ac56b71 Mon Sep 17 00:00:00 2001
From: Andy Kaylor <andrew.kaylor at intel.com>
Date: Fri, 19 Apr 2024 15:34:03 -0700
Subject: [PATCH] [Driver] Introduce ffp-model=aggressive
This change modifies -ffp-model=fast to select options that more closely
match -funsafe-math-optimizations, and introduces a new model,
-ffp-model=aggressive which matches the existing behavior (except for a
minor change in the fp-contract behavior).
The primary motivation for this change is to make -ffp-model=fast more
user friendly, particularly in light of LLVM's aggressive optimizations
when -fno-honor-nans and -fno-honor-infinites are used.
This was previously proposed here:
https://discourse.llvm.org/t/making-ffp-model-fast-more-user-friendly/78402
---
clang/docs/ReleaseNotes.rst | 11 +++++++
clang/docs/UsersManual.rst | 45 ++++++++++++++------------
clang/lib/Driver/ToolChain.cpp | 2 +-
clang/lib/Driver/ToolChains/Clang.cpp | 46 ++++++++++++++++-----------
clang/test/CodeGen/ffp-model.c | 35 +++++++++++++++-----
clang/test/Driver/fp-model.c | 4 +--
6 files changed, 94 insertions(+), 49 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 65de90f69e198..7e3fb64c0efb3 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -102,6 +102,17 @@ Deprecated Compiler Flags
Modified Compiler Flags
-----------------------
+- The ``-ffp-model`` option has been updated to enable a more limited set of
+ optimizations when the ``fast`` argument is used and to accept a new argument,
+ ``aggressive``. The behavior of ``-ffp-model=aggressive`` is mostly equivalent
+ to the previous behavior of ``-ffp-model=fast``. The updated
+ ``-ffp-model=fast`` behavior no longer assumes finite math only and uses a
+ the ``promoted`` algorithm for complex division when possible rather than the
+ less robust Smith algorithm. Both ``-ffp-model=fast`` and
+ ``-ffp-model=aggressive`` will now imply ``-ffp-contract=fast-honor-pragmas``
+ rather than ``-ffp-contract=fast``.
+
+
Removed Compiler Flags
-------------------------
diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index e9b95739ea2ab..ea28e9e22bdfe 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -1452,28 +1452,30 @@ describes the various floating point semantic modes and the corresponding option
"fhonor-infinities", "{on, off}"
"fsigned-zeros", "{on, off}"
"freciprocal-math", "{on, off}"
- "allow_approximate_fns", "{on, off}"
+ "fallow-approximate-fns", "{on, off}"
"fassociative-math", "{on, off}"
+ "fcomplex-arithmetic", "{basic, improved, full, promoted}"
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"
- "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"
+ :header: "Mode", "Precise", "Strict", "Fast", "Aggressive"
+ :widths: 25, 25, 25, 25, 25
+
+ "except_behavior", "ignore", "strict", "ignore", "ignore"
+ "fenv_access", "off", "on", "off", "off"
+ "rounding_mode", "tonearest", "dynamic", "tonearest", "tonearest"
+ "contract", "on", "off", "fast-honor-pragmas", "fast-honor-pragmas"
+ "support_math_errno", "on", "on", "off", "off"
+ "no_honor_nans", "off", "off", "off", "on"
+ "no_honor_infinities", "off", "off", "off", "on"
+ "no_signed_zeros", "off", "off", "on", "on"
+ "allow_reciprocal", "off", "off", "on", "on"
+ "allow_approximate_fns", "off", "off", "on", "on"
+ "allow_reassociation", "off", "off", "on", "on"
+ "complex_arithmetic", "full", "full", "promoted", "basic"
The ``-ffp-model`` option does not modify the ``fdenormal-fp-math``
setting, but it does have an impact on whether ``crtfastmath.o`` is
@@ -1492,9 +1494,9 @@ for more details.
* Floating-point math obeys regular algebraic rules for real numbers (e.g.
``+`` and ``*`` are associative, ``x/y == x * (1/y)``, and
``(a + b) * c == a * c + b * c``),
- * Operands to floating-point operations are not equal to ``NaN`` and
- ``Inf``, and
- * ``+0`` and ``-0`` are interchangeable.
+ * No ``NaN`` or infinite values will be operands or results of
+ floating-point operations,
+ * ``+0`` and ``-0`` may be treated as interchangeable.
``-ffast-math`` also defines the ``__FAST_MATH__`` preprocessor
macro. Some math libraries recognize this macro and change their behavior.
@@ -1753,7 +1755,7 @@ for more details.
Specify floating point behavior. ``-ffp-model`` is an umbrella
option that encompasses functionality provided by other, single
purpose, floating point options. Valid values are: ``precise``, ``strict``,
- and ``fast``.
+ ``fast``, and ``aggressive``.
Details:
* ``precise`` Disables optimizations that are not value-safe on
@@ -1766,7 +1768,10 @@ for more details.
``STDC FENV_ACCESS``: by default ``FENV_ACCESS`` is disabled. This option
setting behaves as though ``#pragma STDC FENV_ACCESS ON`` appeared at the
top of the source file.
- * ``fast`` Behaves identically to specifying both ``-ffast-math`` and
+ * ``fast`` Behaves identically to specifying ``-funsafe-math-optimizations``,
+ ``-fno-math-errno`` and ``-fcomplex-arithmetic=promoted``
+ ``ffp-contract=fast``
+ * ``aggressive`` Behaves identically to specifying both ``-ffast-math`` and
``ffp-contract=fast``
Note: If your command line specifies multiple instances
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 20a555afb8092..49555109b6173 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -1337,7 +1337,7 @@ bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args,
Default = false;
if (A && A->getOption().getID() == options::OPT_ffp_model_EQ) {
StringRef Model = A->getValue();
- if (Model != "fast")
+ if (Model != "fast" && Model != "aggressive")
Default = false;
}
}
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index df1bb8e9ee308..41863eeea395c 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2880,9 +2880,19 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
std::string GccRangeComplexOption = "";
// Lambda to set fast-math options. This is also used by -ffp-model=fast
- auto applyFastMath = [&]() {
- HonorINFs = false;
- HonorNaNs = false;
+ auto applyFastMath = [&](bool Aggressive) {
+ LangOptions::ComplexRangeKind NewRange;
+ if (Aggressive) {
+ HonorINFs = false;
+ HonorNaNs = false;
+ FPContract = "fast";
+ NewRange = LangOptions::ComplexRangeKind::CX_Basic;
+ } else {
+ HonorINFs = true;
+ HonorNaNs = true;
+ FPContract = "fast-honor-pragmas";
+ NewRange = LangOptions::ComplexRangeKind::CX_Promoted;
+ }
MathErrno = false;
AssociativeMath = true;
ReciprocalMath = true;
@@ -2891,21 +2901,16 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
TrappingMath = false;
RoundingFPMath = false;
FPExceptionBehavior = "";
- // If fast-math is set then set the fp-contract mode to fast.
- FPContract = "fast";
- // ffast-math enables basic range rules for complex multiplication and
- // division.
// Warn if user expects to perform full implementation of complex
// multiplication or division in the presence of nan or ninf flags.
- if (Range == LangOptions::ComplexRangeKind::CX_Full ||
- Range == LangOptions::ComplexRangeKind::CX_Improved ||
- Range == LangOptions::ComplexRangeKind::CX_Promoted)
+ if (Range != NewRange)
EmitComplexRangeDiag(
- D, ComplexArithmeticStr(Range),
+ D,
!GccRangeComplexOption.empty()
? GccRangeComplexOption
- : ComplexArithmeticStr(LangOptions::ComplexRangeKind::CX_Basic));
- Range = LangOptions::ComplexRangeKind::CX_Basic;
+ : ComplexArithmeticStr(Range),
+ ComplexArithmeticStr(NewRange));
+ Range = NewRange;
SeenUnsafeMathModeOption = true;
};
@@ -3033,8 +3038,8 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
SignedZeros = true;
StringRef Val = A->getValue();
- if (OFastEnabled && Val != "fast") {
- // Only -ffp-model=fast is compatible with OFast, ignore.
+ if (OFastEnabled && Val != "aggressive") {
+ // Only -ffp-model=aggressive is compatible with OFast, ignore.
D.Diag(clang::diag::warn_drv_overriding_option)
<< Args.MakeArgString("-ffp-model=" + Val) << "-Ofast";
break;
@@ -3046,10 +3051,15 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
<< Args.MakeArgString("-ffp-model=" + Val);
if (Val == "fast") {
FPModel = Val;
- applyFastMath();
+ applyFastMath(false);
// applyFastMath sets fp-contract="fast"
LastFpContractOverrideOption = "-ffp-model=fast";
- } else if (Val == "precise") {
+ } else if (Val.equals("aggressive")) {
+ FPModel = Val;
+ applyFastMath(true);
+ // applyFastMath sets fp-contract="fast"
+ LastFpContractOverrideOption = "-ffp-model=aggressive";
+ } else if (Val.equals("precise")) {
FPModel = Val;
FPContract = "on";
LastFpContractOverrideOption = "-ffp-model=precise";
@@ -3241,7 +3251,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
continue;
[[fallthrough]];
case options::OPT_ffast_math:
- applyFastMath();
+ applyFastMath(true);
if (A->getOption().getID() == options::OPT_Ofast)
LastFpContractOverrideOption = "-Ofast";
else
diff --git a/clang/test/CodeGen/ffp-model.c b/clang/test/CodeGen/ffp-model.c
index 4ed9b9dc0a780..5516ccb218b03 100644
--- a/clang/test/CodeGen/ffp-model.c
+++ b/clang/test/CodeGen/ffp-model.c
@@ -3,6 +3,9 @@
// RUN: %clang -S -emit-llvm -fenable-matrix -ffp-model=fast %s -o - \
// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-FAST
+// RUN: %clang -S -emit-llvm -fenable-matrix -ffp-model=aggressive %s -o - \
+// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-AGGRESSIVE
+
// RUN: %clang -S -emit-llvm -fenable-matrix -ffp-model=precise %s -o - \
// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-PRECISE
@@ -20,9 +23,13 @@ float mymuladd(float x, float y, float z) {
// CHECK: define{{.*}} float @mymuladd
return x * y + z;
- // CHECK-FAST: fmul fast float
+ // CHECK-AGGRESSIVE: fmul fast float
+ // CHECK-AGGRESSIVE: load float, ptr
+ // CHECK-AGGRESSIVE: fadd fast float
+
+ // CHECK-FAST: fmul reassoc nsz arcp contract afn float
// CHECK-FAST: load float, ptr
- // CHECK-FAST: fadd fast float
+ // CHECK-FAST: fadd reassoc nsz arcp contract afn float
// CHECK-PRECISE: load float, ptr
// CHECK-PRECISE: load float, ptr
@@ -54,9 +61,13 @@ void my_vec_muladd(v2f x, float y, v2f z, v2f *res) {
// CHECK: define{{.*}}@my_vec_muladd
*res = x * y + z;
- // CHECK-FAST: fmul fast <2 x float>
+ // CHECK-AGGRESSIVE: fmul fast <2 x float>
+ // CHECK-AGGRESSIVE: load <2 x float>, ptr
+ // CHECK-AGGRESSIVE: fadd fast <2 x float>
+
+ // CHECK-FAST: fmul reassoc nsz arcp contract afn <2 x float>
// CHECK-FAST: load <2 x float>, ptr
- // CHECK-FAST: fadd fast <2 x float>
+ // CHECK-FAST: fadd reassoc nsz arcp contract afn <2 x float>
// CHECK-PRECISE: load <2 x float>, ptr
// CHECK-PRECISE: load float, ptr
@@ -88,9 +99,13 @@ void my_m21_muladd(m21f x, float y, m21f z, m21f *res) {
// CHECK: define{{.*}}@my_m21_muladd
*res = x * y + z;
- // CHECK-FAST: fmul fast <2 x float>
+ // CHECK-AGGRESSIVE: fmul fast <2 x float>
+ // CHECK-AGGRESSIVE: load <2 x float>, ptr
+ // CHECK-AGGRESSIVE: fadd fast <2 x float>
+
+ // CHECK-FAST: fmul reassoc nsz arcp contract afn <2 x float>
// CHECK-FAST: load <2 x float>, ptr
- // CHECK-FAST: fadd fast <2 x float>
+ // CHECK-FAST: fadd reassoc nsz arcp contract afn <2 x float>
// CHECK-PRECISE: load <2 x float>, ptr
// CHECK-PRECISE: load float, ptr
@@ -122,9 +137,13 @@ void my_m22_muladd(m22f x, float y, m22f z, m22f *res) {
// CHECK: define{{.*}}@my_m22_muladd
*res = x * y + z;
- // CHECK-FAST: fmul fast <4 x float>
+ // CHECK-AGGRESSIVE: fmul fast <4 x float>
+ // CHECK-AGGRESSIVE: load <4 x float>, ptr
+ // CHECK-AGGRESSIVE: fadd fast <4 x float>
+
+ // CHECK-FAST: fmul reassoc nsz arcp contract afn <4 x float>
// CHECK-FAST: load <4 x float>, ptr
- // CHECK-FAST: fadd fast <4 x float>
+ // CHECK-FAST: fadd reassoc nsz arcp contract afn <4 x float>
// CHECK-PRECISE: load <4 x float>, ptr
// CHECK-PRECISE: load float, ptr
diff --git a/clang/test/Driver/fp-model.c b/clang/test/Driver/fp-model.c
index 2348d4b41f43a..d15dcad725a8f 100644
--- a/clang/test/Driver/fp-model.c
+++ b/clang/test/Driver/fp-model.c
@@ -2,11 +2,11 @@
// and other floating point options get a warning diagnostic.
//
-// RUN: %clang -### -ffp-model=fast -ffp-contract=off -c %s 2>&1 \
+// RUN: %clang -### -ffp-model=aggressive -ffp-contract=off -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=WARN %s
// WARN: warning: overriding '-ffp-model=fast' option with '-ffp-contract=off' [-Woverriding-option]
-// RUN: %clang -### -ffp-model=fast -ffp-contract=on -c %s 2>&1 \
+// RUN: %clang -### -ffp-model=aggressive -ffp-contract=on -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=WARN1 %s
// WARN1: warning: overriding '-ffp-model=fast' option with '-ffp-contract=on' [-Woverriding-option]
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