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Enable logf128 constant folding for hosts with 128bit long double #104929

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merged 4 commits into from
Aug 22, 2024
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Merged

Enable logf128 constant folding for hosts with 128bit long double #104929

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6bd959c
Enable logf128 constant folding for hosts with 128bit long double
MDevereau Aug 19, 2024
77bae12
Use Api.extractBitsAsZExtValue
MDevereau Aug 20, 2024
b45d146
Remove stray semi-colon
MDevereau Aug 20, 2024
5961bc5
Move common code to ConvertToQuad
MDevereau Aug 21, 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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18 changes: 7 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 +260,13 @@ 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)
check_symbol_exists(__powerpc64le__ "" __PPC64LE)
if(HAS_LOGF128 AND NOT __PPC64LE)
set(LLVM_HAS_LOGF128 On)
add_compile_definitions(HAS_LOGF128)
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Shouldn't this have a cmakedefine entry in llvm/Config/config.h.cmake instead?

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This was meant to always be enabled if available, and thus cmake would do a test and define the cmake variable LLVM_HAS_LOGF128 if the test passed. This patch has been reverted now, but what is likely to happen is this behaviour will be enabled by default, but be eligible to opt-out via a cmake definition which will have an entry in llvm/Config/config.h.cmake

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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15 changes: 3 additions & 12 deletions llvm/include/llvm/ADT/APFloat.h
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Expand Up @@ -19,7 +19,6 @@
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/FloatingPointMode.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/float128.h"
#include <memory>

#define APFLOAT_DISPATCH_ON_SEMANTICS(METHOD_CALL) \
Expand Down Expand Up @@ -378,9 +377,6 @@ class IEEEFloat final : public APFloatBase {
Expected<opStatus> convertFromString(StringRef, roundingMode);
APInt bitcastToAPInt() const;
double convertToDouble() const;
#ifdef HAS_IEE754_FLOAT128
float128 convertToQuad() const;
#endif
float convertToFloat() const;

/// @}
Expand Down Expand Up @@ -1274,14 +1270,9 @@ class APFloat : public APFloatBase {
/// shorter semantics, like IEEEsingle and others.
double convertToDouble() const;

/// Converts this APFloat to host float value.
///
/// \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
float128 convertToQuad() const;
#endif
/// Return true if this APFloat has quadruple precision floating point
/// semantics
bool isValidIEEEQuad() const;

/// Converts this APFloat to host float value.
///
Expand Down
8 changes: 0 additions & 8 deletions llvm/include/llvm/ADT/APInt.h
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Expand Up @@ -17,7 +17,6 @@

#include "llvm/Support/Compiler.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/float128.h"
#include <cassert>
#include <climits>
#include <cstring>
Expand Down Expand Up @@ -1679,13 +1678,6 @@ class [[nodiscard]] APInt {
/// any bit width. Exactly 64 bits will be translated.
double bitsToDouble() const { return llvm::bit_cast<double>(getWord(0)); }

#ifdef HAS_IEE754_FLOAT128
float128 bitsToQuad() const {
__uint128_t ul = ((__uint128_t)U.pVal[1] << 64) + U.pVal[0];
return llvm::bit_cast<float128>(ul);
}
#endif

/// Converts APInt bits to a float
///
/// The conversion does not do a translation from integer to float, it just
Expand Down
14 changes: 6 additions & 8 deletions llvm/include/llvm/Support/float128.h
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Expand Up @@ -9,18 +9,16 @@
#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 !defined(__LONG_DOUBLE_IBM128__) && (__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 @@ -162,9 +162,3 @@ 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()
30 changes: 24 additions & 6 deletions llvm/lib/Analysis/ConstantFolding.cpp
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Expand Up @@ -54,6 +54,7 @@
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/float128.h"
#include <cassert>
#include <cerrno>
#include <cfenv>
Expand Down Expand Up @@ -1741,7 +1742,7 @@ Constant *GetConstantFoldFPValue(double V, Type *Ty) {
llvm_unreachable("Can only constant fold half/float/double");
}

#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
#if defined(HAS_IEE754_FLOAT128)
Constant *GetConstantFoldFPValue128(float128 V, Type *Ty) {
if (Ty->isFP128Ty())
return ConstantFP::get(Ty, V);
Expand Down Expand Up @@ -1781,11 +1782,25 @@ Constant *ConstantFoldFP(double (*NativeFP)(double), const APFloat &V,
return GetConstantFoldFPValue(Result, Ty);
}

#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
#if defined(HAS_IEE754_FLOAT128)
float128 ConvertToQuad(const APFloat &Apf) {
APInt Api = Apf.bitcastToAPInt();
__uint128_t Uint128 =
((__uint128_t)Api.extractBitsAsZExtValue(64, 64) << 64) +
Api.extractBitsAsZExtValue(64, 0);
return llvm::bit_cast<float128>(Uint128);
}
#endif

#if defined(HAS_IEE754_FLOAT128)
Constant *ConstantFoldFP128(float128 (*NativeFP)(float128), const APFloat &V,
Type *Ty) {
llvm_fenv_clearexcept();
float128 Result = NativeFP(V.convertToQuad());
if (!V.isValidIEEEQuad())
return nullptr;

float128 Result = NativeFP(ConvertToQuad(V));

if (llvm_fenv_testexcept()) {
llvm_fenv_clearexcept();
return nullptr;
Expand Down Expand Up @@ -2114,13 +2129,16 @@ 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());
APFloat Value = Op->getValueAPF();
if (!Value.isValidIEEEQuad())
return nullptr;

float128 Result = logf128(ConvertToQuad(Value));
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APFloat should have a software emulator that behaves bit-identical.
Then, the native logf128 may be used as an optimization in it.

return GetConstantFoldFPValue128(Result, Ty);
}

LibFunc Fp128Func = NotLibFunc;
if (TLI->getLibFunc(Name, Fp128Func) && TLI->has(Fp128Func) &&
Fp128Func == LibFunc_logl)
Expand Down
24 changes: 2 additions & 22 deletions llvm/lib/Support/APFloat.cpp
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Expand Up @@ -3749,15 +3749,6 @@ double IEEEFloat::convertToDouble() const {
return api.bitsToDouble();
}

#ifdef HAS_IEE754_FLOAT128
float128 IEEEFloat::convertToQuad() const {
assert(semantics == (const llvm::fltSemantics *)&semIEEEquad &&
"Float semantics are not IEEEquads");
APInt api = bitcastToAPInt();
return api.bitsToQuad();
}
#endif

/// Integer bit is explicit in this format. Intel hardware (387 and later)
/// does not support these bit patterns:
/// exponent = all 1's, integer bit 0, significand 0 ("pseudoinfinity")
Expand Down Expand Up @@ -5406,20 +5397,9 @@ double APFloat::convertToDouble() const {
return Temp.getIEEE().convertToDouble();
}

#ifdef HAS_IEE754_FLOAT128
float128 APFloat::convertToQuad() const {
if (&getSemantics() == (const llvm::fltSemantics *)&semIEEEquad)
return getIEEE().convertToQuad();
assert(getSemantics().isRepresentableBy(semIEEEquad) &&
"Float semantics is not representable by IEEEquad");
APFloat Temp = *this;
bool LosesInfo;
opStatus St = Temp.convert(semIEEEquad, rmNearestTiesToEven, &LosesInfo);
assert(!(St & opInexact) && !LosesInfo && "Unexpected imprecision");
(void)St;
return Temp.getIEEE().convertToQuad();
bool APFloat::isValidIEEEQuad() const {
return (&getSemantics() == (const llvm::fltSemantics *)&semIEEEquad);
}
#endif

float APFloat::convertToFloat() const {
if (&getSemantics() == (const llvm::fltSemantics *)&semIEEEsingle)
Expand Down
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