[APFloat] Add exp function for APFloat::IEEESsingle using expf implementation from LLVM libc.

libc/src/__support/math/expf.h

@@ -109,6 +109,22 @@ static constexpr float expf(float x) {
   return static_cast<float>(exp_hi * exp_mid * exp_lo);
 }
 
+#pragma STDC FENV_ACCESS ON
+
+// Directional rounding version of expf.
+LIBC_INLINE static float expf(float x, int rounding_mode) {
+  int current_rounding_mode = fputil::get_round();
+  if (rounding_mode == current_rounding_mode)
+    return expf(x);
+
+  fputil::set_round(rounding_mode);
+  float result = expf(x);
+  fputil::set_round(current_rounding_mode);
+  return result;
+}
+
+#pragma STDC FENV_ACCESS DEFAULT
+
 } // namespace math
 
 } // namespace LIBC_NAMESPACE_DECL

llvm/CMakeLists.txt

@@ -659,6 +659,11 @@ endif()
 
 set(LLVM_ENABLE_Z3_SOLVER_DEFAULT "${Z3_FOUND}")
 
+include(FindLibcCommonUtils)
+if(NOT TARGET llvm-libc-common-utilities)
+  message(FATAL_ERROR "LLVM libc is not found at ${libc_path}.")
+endif()
+
 
 if( LLVM_TARGETS_TO_BUILD STREQUAL "all" )
   set( LLVM_TARGETS_TO_BUILD ${LLVM_ALL_TARGETS} )

llvm/include/llvm/ADT/APFloat.h

@@ -1525,6 +1525,8 @@ class APFloat : public APFloatBase {
   friend APFloat frexp(const APFloat &X, int &Exp, roundingMode RM);
   friend IEEEFloat;
   friend DoubleAPFloat;
+
+  friend APFloat exp(const APFloat &X, roundingMode RM);
 };
 
 static_assert(sizeof(APFloat) == sizeof(detail::IEEEFloat),
@@ -1658,6 +1660,10 @@ inline APFloat maximumnum(const APFloat &A, const APFloat &B) {
   return A < B ? B : A;
 }
 
+/// Implement IEEE 754-2019 exp functions.
+LLVM_READONLY
+APFloat exp(const APFloat &X, RoundingMode RM = APFloat::rmNearestTiesToEven);
+
 inline raw_ostream &operator<<(raw_ostream &OS, const APFloat &V) {
   V.print(OS);
   return OS;

llvm/lib/Support/APFloat.cpp

@@ -28,6 +28,9 @@
 #include <cstring>
 #include <limits.h>
 
+// Shared headers from LLVM libc
+#include "shared/math.h"
+
 #define APFLOAT_DISPATCH_ON_SEMANTICS(METHOD_CALL)                             \
   do {                                                                         \
     if (usesLayout<IEEEFloat>(getSemantics()))                                 \
@@ -5601,6 +5604,29 @@ float APFloat::convertToFloat() const {
   return Temp.getIEEE().convertToFloat();
 }
 
+static constexpr int getFEnvRoundingMode(llvm::RoundingMode rm) {
+  switch (rm) {
+  case APFloat::rmTowardPositive:
+    return FE_UPWARD;
+  case APFloat::rmTowardNegative:
+    return FE_DOWNWARD;
+  case APFloat::rmTowardZero:
+    return FE_TOWARDZERO;
+  default:
+    // TODO: fix rmNearestTiesToAway for platform without FE_TONEARESTFROMZERO.
+    return FE_TONEAREST;
+  };
+}
+
+APFloat exp(const APFloat &X, RoundingMode rounding_mode) {
+  if (&X.getSemantics() == &semIEEEsingle) {
+    float result = LIBC_NAMESPACE::shared::expf(
+        X.convertToFloat(), getFEnvRoundingMode(rounding_mode));
+    return APFloat(result);
+  }
+  assert(false && "Unsupported floating-point semantics");
+}
+
 } // namespace llvm
 
 #undef APFLOAT_DISPATCH_ON_SEMANTICS

llvm/lib/Support/CMakeLists.txt

@@ -384,3 +384,7 @@ target_include_directories(LLVMSupport
   PRIVATE
   ${LLVM_THIRD_PARTY_DIR}/siphash/include
 )
+
+# Integrating LLVM libc's math functions
+target_include_directories(LLVMSupport PRIVATE "${LLVM_INCLUDE_DIR}/../../libc")
+target_compile_options(LLVMSupport PRIVATE "-Wno-c99-extensions") # _Complex warnings.

llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp

@@ -1540,7 +1540,7 @@ bool AMDGPULibCalls::evaluateScalarMathFunc(const FuncInfo &FInfo, double &Res0,
     return true;
 
   case AMDGPULibFunc::EI_EXP:
-    Res0 = exp(opr0);
+    Res0 = std::exp(opr0);
     return true;
 
   case AMDGPULibFunc::EI_EXP2:

llvm/unittests/ADT/APFloatTest.cpp

@@ -16,6 +16,7 @@
 #include "llvm/Support/FormatVariadic.h"
 #include "gtest/gtest.h"
 #include <cmath>
+#include <limits>
 #include <ostream>
 #include <string>
 #include <tuple>
@@ -8356,4 +8357,78 @@ TEST(APFloatTest, hasSignBitInMSB) {
   EXPECT_FALSE(APFloat::hasSignBitInMSB(APFloat::Float8E8M0FNU()));
 }
 
+TEST(APFloatTest, expf) {
+  std::array<llvm::RoundingMode, 4> allRoundingModes = {
+      APFloat::rmNearestTiesToEven, APFloat::rmTowardPositive,
+      APFloat::rmTowardNegative, APFloat::rmTowardZero};
+  for (auto rm : allRoundingModes) {
+    // exp(+-0) = 1 for all rounding modes.
+    EXPECT_EQ(1.0f, llvm::exp(APFloat(0.0f), rm).convertToFloat());
+    EXPECT_EQ(1.0f, llvm::exp(APFloat(-0.0f), rm).convertToFloat());
+    // exp(+Inf) = +Inf for all rounding modes.
+    EXPECT_EQ(std::numeric_limits<float>::infinity(),
+              llvm::exp(APFloat::getInf(APFloat::IEEEsingle(), false), rm)
+                  .convertToFloat());
+    // exp(-Inf) = 0 for all rounding modes.
+    EXPECT_EQ(0.0f, llvm::exp(APFloat::getInf(APFloat::IEEEsingle(), true), rm)
+                        .convertToFloat());
+    // exp(NaN) = NaN for all rounding modes.
+    EXPECT_TRUE(llvm::exp(APFloat::getNaN(APFloat::IEEEsingle()), rm).isNaN());
+  }
+  // exp(1)
+  EXPECT_EQ(
+      0x1.5bf0a8p1f,
+      llvm::exp(APFloat(1.0f), APFloat::rmNearestTiesToEven).convertToFloat());
+  EXPECT_EQ(
+      0x1.5bf0aap1f,
+      llvm::exp(APFloat(1.0f), APFloat::rmTowardPositive).convertToFloat());
+  EXPECT_EQ(
+      0x1.5bf0a8p1f,
+      llvm::exp(APFloat(1.0f), APFloat::rmTowardNegative).convertToFloat());
+  EXPECT_EQ(0x1.5bf0a8p1f,
+            llvm::exp(APFloat(1.0f), APFloat::rmTowardZero).convertToFloat());
+  // exp(float max)
+  EXPECT_EQ(std::numeric_limits<float>::infinity(),
+            llvm::exp(APFloat::getLargest(APFloat::IEEEsingle(), false),
+                      APFloat::rmNearestTiesToEven)
+                .convertToFloat());
+  EXPECT_EQ(std::numeric_limits<float>::infinity(),
+            llvm::exp(APFloat::getLargest(APFloat::IEEEsingle(), false),
+                      APFloat::rmTowardPositive)
+                .convertToFloat());
+  EXPECT_EQ(std::numeric_limits<float>::max(),
+            llvm::exp(APFloat::getLargest(APFloat::IEEEsingle(), false),
+                      APFloat::rmTowardNegative)
+                .convertToFloat());
+  EXPECT_EQ(std::numeric_limits<float>::max(),
+            llvm::exp(APFloat::getLargest(APFloat::IEEEsingle(), false),
+                      APFloat::rmTowardZero)
+                .convertToFloat());
+  // exp(min_denormal)
+  EXPECT_EQ(1.0f, llvm::exp(APFloat::getSmallest(APFloat::IEEEsingle(), false),
+                            APFloat::rmNearestTiesToEven)
+                      .convertToFloat());
+  EXPECT_EQ(0x1.000002p0f,
+            llvm::exp(APFloat::getSmallest(APFloat::IEEEsingle(), false),
+                      APFloat::rmTowardPositive)
+                .convertToFloat());
+  EXPECT_EQ(1.0f, llvm::exp(APFloat::getSmallest(APFloat::IEEEsingle(), false),
+                            APFloat::rmTowardNegative)
+                      .convertToFloat());
+  EXPECT_EQ(1.0f, llvm::exp(APFloat::getSmallest(APFloat::IEEEsingle(), false),
+                            APFloat::rmTowardZero)
+                      .convertToFloat());
+  // Default rounding mode.
+  // exp(-1)
+  EXPECT_EQ(0x1.78b564p-2f, llvm::exp(APFloat(-1.0f)).convertToFloat());
+  EXPECT_EQ(
+      0x1.78b564p-2f,
+      llvm::exp(APFloat(-1.0f), APFloat::rmTowardPositive).convertToFloat());
+  EXPECT_EQ(
+      0x1.78b562p-2f,
+      llvm::exp(APFloat(-1.0f), APFloat::rmTowardNegative).convertToFloat());
+  EXPECT_EQ(0x1.78b562p-2f,
+            llvm::exp(APFloat(-1.0f), APFloat::rmTowardZero).convertToFloat());
+}
+
 } // namespace