Revert "Enable logf128 constant folding for hosts with 128bit long double (#104929)"

chapuni · chapuni · commit 3ef64f7ab5b8 · 2024-08-25T08:30:23.000+09:00
ConstantFolding behaves differently depending on host's `HAS_IEE754_FLOAT128`. LLVM should not change the behavior depending on host configurations. This reverts commit 14c7e4a. (llvmorg-20-init-3262-g14c7e4a18449 and llvmorg-20-init-3498-g001e423ac626)
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
@@ -560,6 +560,8 @@ 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.")
diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
@@ -246,6 +246,17 @@ 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 "${HAS_LOGF128}")
+endif()
+
 # function checks
 check_symbol_exists(arc4random "stdlib.h" HAVE_DECL_ARC4RANDOM)
 find_package(Backtrace)
@@ -259,13 +270,6 @@ if(C_SUPPORTS_WERROR_UNGUARDED_AVAILABILITY_NEW)
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -Werror=unguarded-availability-new")
 endif()
 
-check_cxx_symbol_exists(logf128 cmath HAS_LOGF128)
-check_symbol_exists(__powerpc__ "" __PPC64LE)
-if(HAS_LOGF128 AND NOT __PPC64LE)
-    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)
diff --git a/llvm/include/llvm/ADT/APFloat.h b/llvm/include/llvm/ADT/APFloat.h
@@ -19,6 +19,7 @@
 #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)                             \
@@ -377,6 +378,9 @@ 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;
 
   /// @}
@@ -1270,9 +1274,14 @@ class APFloat : public APFloatBase {
   /// shorter semantics, like IEEEsingle and others.
   double convertToDouble() const;
 
-  /// Return true if this APFloat has quadruple precision floating point
-  /// semantics
-  bool isValidIEEEQuad() 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
 
   /// Converts this APFloat to host float value.
   ///
diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
@@ -17,6 +17,7 @@
 
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/float128.h"
 #include <cassert>
 #include <climits>
 #include <cstring>
@@ -1676,6 +1677,13 @@ 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
diff --git a/llvm/include/llvm/Support/float128.h b/llvm/include/llvm/Support/float128.h
@@ -9,16 +9,18 @@
 #ifndef LLVM_FLOAT128
 #define LLVM_FLOAT128
 
-#include <cmath>
-
 namespace llvm {
 
-#ifdef HAS_LOGF128
-#if !defined(__LONG_DOUBLE_IBM128__) && (__SIZEOF_INT128__ == 16)
-typedef decltype(logf128(0.)) float128;
+#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__))
 #define HAS_IEE754_FLOAT128
+typedef _Float128 float128;
 #endif
-#endif // HAS_LOGF128
 
 } // namespace llvm
 #endif // LLVM_FLOAT128
diff --git a/llvm/lib/Analysis/CMakeLists.txt b/llvm/lib/Analysis/CMakeLists.txt
@@ -162,3 +162,9 @@ 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()
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -54,7 +54,6 @@
 #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>
@@ -1742,7 +1741,7 @@ Constant *GetConstantFoldFPValue(double V, Type *Ty) {
   llvm_unreachable("Can only constant fold half/float/double");
 }
 
-#if defined(HAS_IEE754_FLOAT128)
+#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
 Constant *GetConstantFoldFPValue128(float128 V, Type *Ty) {
   if (Ty->isFP128Ty())
     return ConstantFP::get(Ty, V);
@@ -1782,25 +1781,11 @@ Constant *ConstantFoldFP(double (*NativeFP)(double), const APFloat &V,
   return GetConstantFoldFPValue(Result, Ty);
 }
 
-#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)
+#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
 Constant *ConstantFoldFP128(float128 (*NativeFP)(float128), const APFloat &V,
                             Type *Ty) {
   llvm_fenv_clearexcept();
-  if (!V.isValidIEEEQuad())
-    return nullptr;
-
-  float128 Result = NativeFP(ConvertToQuad(V));
-
+  float128 Result = NativeFP(V.convertToQuad());
   if (llvm_fenv_testexcept()) {
     llvm_fenv_clearexcept();
     return nullptr;
@@ -2129,16 +2114,13 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
     if (IntrinsicID == Intrinsic::canonicalize)
       return constantFoldCanonicalize(Ty, Call, U);
 
-#if defined(HAS_IEE754_FLOAT128)
+#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
     if (Ty->isFP128Ty()) {
       if (IntrinsicID == Intrinsic::log) {
-        APFloat Value = Op->getValueAPF();
-        if (!Value.isValidIEEEQuad())
-          return nullptr;
-
-        float128 Result = logf128(ConvertToQuad(Value));
+        float128 Result = logf128(Op->getValueAPF().convertToQuad());
         return GetConstantFoldFPValue128(Result, Ty);
       }
+
       LibFunc Fp128Func = NotLibFunc;
       if (TLI && TLI->getLibFunc(Name, Fp128Func) && TLI->has(Fp128Func) &&
           Fp128Func == LibFunc_logl)
diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
@@ -3749,6 +3749,15 @@ 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")
@@ -5397,9 +5406,20 @@ double APFloat::convertToDouble() const {
   return Temp.getIEEE().convertToDouble();
 }
 
-bool APFloat::isValidIEEEQuad() const {
-  return (&getSemantics() == (const llvm::fltSemantics *)&semIEEEquad);
+#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();
 }
+#endif
 
 float APFloat::convertToFloat() const {
   if (&getSemantics() == (const llvm::fltSemantics *)&semIEEEsingle)
