[clang] Align -ffp-model=fast denormal handling with -ffast-math (PR #89477)
Andy Kaylor via cfe-commits
cfe-commits at lists.llvm.org
Fri Apr 19 18:02:23 PDT 2024
https://github.com/andykaylor created https://github.com/llvm/llvm-project/pull/89477
This is an attempt to better align the denormal handling of
-ffp-model=fast with the behavior of -ffast-math. The clang user's
manual claims that -ffp-model=fast "behaves identically to specifying
both -ffast-math and -ffp-contract=fast." That isn't entirely correct.
One difference is that -ffast-math causes crtfastmath.o to be linked if
it is available, and passes -fdenormal-fp-math=PreserveSign as a -cc1
option when crtfastmath.o is available.
I'm not sure the current behavior is reasonable and consistent for all
tool chains, but I'm not trying to fix that here. This is just trying to
make an incremental improvement.
I am going to be proposing further changes to -ffp-model=fast,
decoupling it from -ffast-math and introducing a new
-ffp-model=aggressive that matches the current behavior, but I wanted
to solidfy the current behavior before I do that.
>From cd8df1939a456c05a1d94c471627fc5a7a332fc1 Mon Sep 17 00:00:00 2001
From: Andy Kaylor <andrew.kaylor at intel.com>
Date: Fri, 19 Apr 2024 17:53:52 -0700
Subject: [PATCH] Align -ffp-model=fast denormal handling with -ffast-math
This is an attempt to better align the denormal handling of
-ffp-model=fast with the behavior of -ffast-math. The clang user's
manual claims that -ffp-model=fast "behaves identically to specifying
both -ffast-math and -ffp-contract=fast." That isn't entirely correct.
One difference is that -ffast-math causes crtfastmath.o to be linked if
it is available, and passes -fdenormal-fp-math=PreserveSign as a -cc1
option when crtfastmath.o is available.
I'm not sure the current behavior is reasonable and consistent for all
tool chains, but I'm not trying to fix that here. This is just trying to
make an incremental improvement.
I am going to be proposing further changes to -ffp-model=fast,
decoupling it from -ffast-math and introducing a new
-ffp-model=aggressive that matches the current behavior, but I wanted
to solidfy the current behavior before I do that.
---
clang/docs/UsersManual.rst | 4 ++--
clang/lib/Driver/ToolChain.cpp | 8 +++++++-
clang/lib/Driver/ToolChains/Clang.cpp | 4 ++++
clang/test/Driver/default-denormal-fp-math.c | 3 +++
clang/test/Driver/linux-ld.c | 3 +++
clang/test/Driver/solaris-ld.c | 3 +++
6 files changed, 22 insertions(+), 3 deletions(-)
diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index c464bc3a69adc5..00bb1e779308ef 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -1452,8 +1452,8 @@ floating point semantic models: precise (the default), strict, and fast.
"fenv_access", "off", "on", "off"
"rounding_mode", "tonearest", "dynamic", "tonearest"
"contract", "on", "off", "fast"
- "denormal_fp_math", "IEEE", "IEEE", "IEEE"
- "denormal_fp32_math", "IEEE","IEEE", "IEEE"
+ "denormal_fp_math", "IEEE", "IEEE", "target-dependent"
+ "denormal_fp32_math", "IEEE","IEEE", "target-dependent"
"support_math_errno", "on", "on", "off"
"no_honor_nans", "off", "off", "on"
"no_honor_infinities", "off", "off", "on"
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 237092ed07e5dc..a36d8eb1750a2d 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -1314,11 +1314,17 @@ bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args,
Arg *A =
Args.getLastArg(options::OPT_ffast_math, options::OPT_fno_fast_math,
options::OPT_funsafe_math_optimizations,
- options::OPT_fno_unsafe_math_optimizations);
+ options::OPT_fno_unsafe_math_optimizations,
+ options::OPT_ffp_model_EQ);
if (!A || A->getOption().getID() == options::OPT_fno_fast_math ||
A->getOption().getID() == options::OPT_fno_unsafe_math_optimizations)
return false;
+ if (A && A->getOption().getID() == options::OPT_ffp_model_EQ) {
+ StringRef Model = A->getValue();
+ if (!Model.equals("fast"))
+ return false;
+ }
}
// If crtfastmath.o exists add it to the arguments.
Path = GetFilePath("crtfastmath.o");
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 456ea74caadb00..0ee74855891b03 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2942,6 +2942,10 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
if (Val.equals("fast")) {
FPModel = Val;
applyFastMath();
+ // The target-specific getDefaultDenormalModeForType handler should
+ // account for -ffp-model=fast and choose its behavior
+ DenormalFPMath = DefaultDenormalFPMath;
+ DenormalFP32Math = DefaultDenormalFP32Math;
} else if (Val.equals("precise")) {
optID = options::OPT_ffp_contract;
FPModel = Val;
diff --git a/clang/test/Driver/default-denormal-fp-math.c b/clang/test/Driver/default-denormal-fp-math.c
index 5f87e151df49e4..61787a8bbe82b8 100644
--- a/clang/test/Driver/default-denormal-fp-math.c
+++ b/clang/test/Driver/default-denormal-fp-math.c
@@ -5,12 +5,15 @@
// crtfastmath enables ftz and daz
// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffp-model=fast --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s
// crt not linked in with nostartfiles
// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math -nostartfiles --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffp-model=fast -nostartfiles --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
// If there's no crtfastmath, don't assume ftz/daz
// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=/dev/null -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffp-model=fast --sysroot=/dev/null -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
// RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s
diff --git a/clang/test/Driver/linux-ld.c b/clang/test/Driver/linux-ld.c
index d918f4f2d7dbd9..a3ad564082b966 100644
--- a/clang/test/Driver/linux-ld.c
+++ b/clang/test/Driver/linux-ld.c
@@ -1417,6 +1417,9 @@
// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -funsafe-math-optimizations\
// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffp-model=fast \
+// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -Ofast\
// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
diff --git a/clang/test/Driver/solaris-ld.c b/clang/test/Driver/solaris-ld.c
index 6d74389e89222c..ce0728d392bf23 100644
--- a/clang/test/Driver/solaris-ld.c
+++ b/clang/test/Driver/solaris-ld.c
@@ -193,6 +193,9 @@
// RUN: %clang --target=sparc-sun-solaris2.11 -### %s -ffast-math \
// RUN: --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH-SPARC32 %s
+// RUN: %clang --target=sparc-sun-solaris2.11 -### %s -ffp-model=fast \
+// RUN: --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH-SPARC32 %s
// CHECK-CRTFASTMATH-SPARC32: "-isysroot" "[[SYSROOT:[^"]+]]"
// CHECK-CRTFASTMATH-SPARC32: "[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2{{/|\\\\}}crtfastmath.o"
// CHECK-NOCRTFASTMATH-SPARC32-NOT: crtfastmath.o
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