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Enable logf128 constant folding for hosts with 128bit long double #96287

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Merged
merged 8 commits into from
Aug 9, 2024
Merged

Enable logf128 constant folding for hosts with 128bit long double #96287

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4cc6905
Enable logf128 constant folding for AArch64
MDevereau Jun 21, 2024
97a0b20
Remove aarch64 constraint
MDevereau Jun 26, 2024
94c6914
Enable optimization without opt-in
MDevereau Jun 26, 2024
422fed8
Check for viable logf128 and use that for float128's typedef
MDevereau Jul 11, 2024
613f6a4
Remove cmake tests
MDevereau Jul 17, 2024
5705316
Lit uses LLVM_HAS_LOGF128 to run tests and is no longer a command lin…
MDevereau Jul 18, 2024
6ceda72
Remove check for __LDBL_MANT_DIG__
MDevereau Aug 6, 2024
cc0a937
Merge branch 'main' into aarch64-logf128
MDevereau Aug 9, 2024
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2 changes: 0 additions & 2 deletions llvm/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -560,8 +560,6 @@ set(LLVM_USE_STATIC_ZSTD FALSE CACHE BOOL "Use static version of zstd. Can be TR

set(LLVM_ENABLE_CURL "OFF" CACHE STRING "Use libcurl for the HTTP client if available. Can be ON, OFF, or FORCE_ON")

set(LLVM_HAS_LOGF128 "OFF" CACHE STRING "Use logf128 to constant fold fp128 logarithm calls. Can be ON, OFF, or FORCE_ON")

set(LLVM_ENABLE_HTTPLIB "OFF" CACHE STRING "Use cpp-httplib HTTP server library if available. Can be ON, OFF, or FORCE_ON")

set(LLVM_Z3_INSTALL_DIR "" CACHE STRING "Install directory of the Z3 solver.")
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17 changes: 6 additions & 11 deletions llvm/cmake/config-ix.cmake
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Expand Up @@ -247,17 +247,6 @@ else()
set(HAVE_LIBEDIT 0)
endif()

if(LLVM_HAS_LOGF128)
include(CheckCXXSymbolExists)
check_cxx_symbol_exists(logf128 math.h HAS_LOGF128)

if(LLVM_HAS_LOGF128 STREQUAL FORCE_ON AND NOT HAS_LOGF128)
message(FATAL_ERROR "Failed to configure logf128")
endif()

set(LLVM_HAS_LOGF128 "${HAS_LOGF128}")
endif()

# function checks
check_symbol_exists(arc4random "stdlib.h" HAVE_DECL_ARC4RANDOM)
find_package(Backtrace)
Expand All @@ -271,6 +260,12 @@ if(C_SUPPORTS_WERROR_UNGUARDED_AVAILABILITY_NEW)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -Werror=unguarded-availability-new")
endif()

check_cxx_symbol_exists(logf128 cmath HAS_LOGF128)
if(HAS_LOGF128)
set(LLVM_HAS_LOGF128 On)
add_compile_definitions(HAS_LOGF128)
endif()

# Determine whether we can register EH tables.
check_symbol_exists(__register_frame "${CMAKE_CURRENT_LIST_DIR}/unwind.h" HAVE_REGISTER_FRAME)
check_symbol_exists(__deregister_frame "${CMAKE_CURRENT_LIST_DIR}/unwind.h" HAVE_DEREGISTER_FRAME)
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4 changes: 2 additions & 2 deletions llvm/include/llvm/ADT/APFloat.h
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Expand Up @@ -370,7 +370,7 @@ class IEEEFloat final : public APFloatBase {
Expected<opStatus> convertFromString(StringRef, roundingMode);
APInt bitcastToAPInt() const;
double convertToDouble() const;
#ifdef HAS_IEE754_FLOAT128
#if defined(HAS_IEE754_FLOAT128)
float128 convertToQuad() const;
#endif
float convertToFloat() const;
Expand Down Expand Up @@ -1267,7 +1267,7 @@ class APFloat : public APFloatBase {
/// \pre The APFloat must be built using semantics, that can be represented by
/// the host float type without loss of precision. It can be IEEEquad and
/// shorter semantics, like IEEEdouble and others.
#ifdef HAS_IEE754_FLOAT128
#if defined(HAS_IEE754_FLOAT128)
float128 convertToQuad() const;
#endif

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15 changes: 7 additions & 8 deletions llvm/include/llvm/Support/float128.h
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Expand Up @@ -9,18 +9,17 @@
#ifndef LLVM_FLOAT128
#define LLVM_FLOAT128

#include <cmath>

namespace llvm {

#if defined(__clang__) && defined(__FLOAT128__) && \
defined(__SIZEOF_INT128__) && !defined(__LONG_DOUBLE_IBM128__)
#define HAS_IEE754_FLOAT128
typedef __float128 float128;
#elif defined(__FLOAT128__) && defined(__SIZEOF_INT128__) && \
!defined(__LONG_DOUBLE_IBM128__) && \
(defined(__GNUC__) || defined(__GNUG__))
#ifdef HAS_LOGF128
#if (__LDBL_MANT_DIG__ == 113) && !defined(__LONG_DOUBLE_IBM128__) && \
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@efriedma-quic efriedma-quic Jul 23, 2024 •
edited
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Is the check for __LDBL_MANT_DIG__ necessary with the current version?

Otherwise, this approach seems fine.

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@efriedma-quic efriedma-quic Jul 23, 2024

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(I was suggesting LDBL_MANT_DIG with the old version that explicitly wrote out the type "long double". It should be safe to assume that if logf128 returns a long double, then long double is actually an IEEE 128-bit float.)

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@MDevereau MDevereau Aug 6, 2024

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Sorry for the late update, I've been away for a few weeks. I believe its unnecessary in this version, if HAS_LOGF128 is true the logf128 function prototype should return a valid IEEE 128-bit float.

I believe this will expose a problem I've seen where x86 targets with fp80 will return a slightly different result from AArch64. I.e., AArch64's 0xL00000000000000007FFF800000000000 vs x86's 0xL0000000000000000FFFF800000000000 for the Constant folding test log_e_negative_infinity and a few others. I'm not sure if this is due to a target specific implementation of logf128 currently.

(__SIZEOF_INT128__ == 16)
typedef decltype(logf128(0.)) float128;
#define HAS_IEE754_FLOAT128
typedef _Float128 float128;
#endif
#endif // HAS_LOGF128

} // namespace llvm
#endif // LLVM_FLOAT128
6 changes: 0 additions & 6 deletions llvm/lib/Analysis/CMakeLists.txt
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Expand Up @@ -159,9 +159,3 @@ add_llvm_component_library(LLVMAnalysis
Support
TargetParser
)

include(CheckCXXSymbolExists)
check_cxx_symbol_exists(logf128 math.h HAS_LOGF128)
if(HAS_LOGF128)
target_compile_definitions(LLVMAnalysis PRIVATE HAS_LOGF128)
endif()
8 changes: 4 additions & 4 deletions llvm/lib/Analysis/ConstantFolding.cpp
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Expand Up @@ -1783,9 +1783,9 @@ Constant *ConstantFoldFP(double (*NativeFP)(double), const APFloat &V,
return GetConstantFoldFPValue(Result, Ty);
}

#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
Constant *ConstantFoldFP128(long double (*NativeFP)(long double),
const APFloat &V, Type *Ty) {
#if defined(HAS_IEE754_FLOAT128)
Constant *ConstantFoldFP128(float128 (*NativeFP)(float128), const APFloat &V,
Type *Ty) {
llvm_fenv_clearexcept();
float128 Result = NativeFP(V.convertToQuad());
if (llvm_fenv_testexcept()) {
Expand Down Expand Up @@ -2116,7 +2116,7 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
if (IntrinsicID == Intrinsic::canonicalize)
return constantFoldCanonicalize(Ty, Call, U);

#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
#if defined(HAS_IEE754_FLOAT128)
if (Ty->isFP128Ty()) {
if (IntrinsicID == Intrinsic::log) {
float128 Result = logf128(Op->getValueAPF().convertToQuad());
Expand Down
4 changes: 2 additions & 2 deletions llvm/lib/Support/APFloat.cpp
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Expand Up @@ -3721,7 +3721,7 @@ double IEEEFloat::convertToDouble() const {
return api.bitsToDouble();
}

#ifdef HAS_IEE754_FLOAT128
#if defined(HAS_IEE754_FLOAT128)
float128 IEEEFloat::convertToQuad() const {
assert(semantics == (const llvm::fltSemantics *)&semIEEEquad &&
"Float semantics are not IEEEquads");
Expand Down Expand Up @@ -5351,7 +5351,7 @@ double APFloat::convertToDouble() const {
return Temp.getIEEE().convertToDouble();
}

#ifdef HAS_IEE754_FLOAT128
#if defined(HAS_IEE754_FLOAT128)
float128 APFloat::convertToQuad() const {
if (&getSemantics() == (const llvm::fltSemantics *)&semIEEEquad)
return getIEEE().convertToQuad();
Expand Down