PR #16775: Add test for EmitReducePrecisionIR

Imported from GitHub PR #16775

I noticed that the `EmitReducePrecisionIR` function from `xla/service/elemental_ir_emitter.h` is not covered by unit tests.

Given its non-trivial logic, I believe it should be thoroughly tested, particularly for corner cases.

Changes in this PR:
- Declare `EmitReducePrecisionIR` function in `xla/service/elemental_ir_emitter.h`
- Add `EmitReducePrecisionIR_F16ToF8e5m2` test
- Add `EmitReducePrecisionIR_F16ToF8e4m3fn` test

Related PR:
- [PR-16585](#16585) Add support for float8_e4m3

Copybara import of the project:

--
5972205 by Alexander Pivovarov <pivovaa@amazon.com>:

Add test for EmitReducePrecisionIR

Merging this change closes #16775

FUTURE_COPYBARA_INTEGRATE_REVIEW=#16775 from apivovarov:elemental_ir_emitter_test 5972205
PiperOrigin-RevId: 696646489

third_party/llvm/generated.patch

@@ -1,13 +1 @@
 Auto generated patch. Do not edit or delete it, even if empty.
-diff -ruN --strip-trailing-cr a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
---- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
-+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
-@@ -1465,7 +1465,7 @@
-           : Suffix;
-
-   ValueSet StructValues;
--  StructType *StructTy;
-+  StructType *StructTy = nullptr;
-   Function *newFunction = constructFunctionDeclaration(
-       inputs, outputs, EntryFreq, oldFunction->getName() + "." + SuffixToUse,
-       StructValues, StructTy);

third_party/llvm/workspace.bzl

@@ -4,8 +4,8 @@ load("//third_party:repo.bzl", "tf_http_archive")
 
 def repo(name):
     """Imports LLVM."""
-    LLVM_COMMIT = "97298853b4de70dbce9c0a140ac38e3ac179e02e"
-    LLVM_SHA256 = "ac811cb61d281043c865c39260a5114a0e96d16ec0e4eb74a2516a24981b9064"
+    LLVM_COMMIT = "03730cdd3d10c5270fe436777a37d50b0838a3bf"
+    LLVM_SHA256 = "54d843249c75b200f7bf9b7947079fe16fa0b657c4aee4abdde4ac05a9cd5f84"
 
     tf_http_archive(
         name = name,

third_party/shardy/workspace.bzl

@@ -3,8 +3,8 @@
 load("//third_party:repo.bzl", "tf_http_archive", "tf_mirror_urls")
 
 def repo():
-    SHARDY_COMMIT = "879e94b974bc47a37263a897fe5fb83d8b52e266"
-    SHARDY_SHA256 = "a08491556df5185b37a4d94fda3ce5c71233f0319b3efbb45f00120fbcad973a"
+    SHARDY_COMMIT = "c3f3c8e9ae90470e24891428072ff8cbc7445e95"
+    SHARDY_SHA256 = "92dd51c7de67e3b0bd09f388f1f71bebb44547a98b33ee9ece66eba0fac439d1"
 
     tf_http_archive(
         name = "shardy",

third_party/tsl/third_party/llvm/generated.patch

@@ -1,13 +1 @@
 Auto generated patch. Do not edit or delete it, even if empty.
-diff -ruN --strip-trailing-cr a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
---- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
-+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
-@@ -1465,7 +1465,7 @@
-           : Suffix;
-
-   ValueSet StructValues;
--  StructType *StructTy;
-+  StructType *StructTy = nullptr;
-   Function *newFunction = constructFunctionDeclaration(
-       inputs, outputs, EntryFreq, oldFunction->getName() + "." + SuffixToUse,
-       StructValues, StructTy);

third_party/tsl/third_party/llvm/workspace.bzl

@@ -4,8 +4,8 @@ load("//third_party:repo.bzl", "tf_http_archive")
 
 def repo(name):
     """Imports LLVM."""
-    LLVM_COMMIT = "97298853b4de70dbce9c0a140ac38e3ac179e02e"
-    LLVM_SHA256 = "ac811cb61d281043c865c39260a5114a0e96d16ec0e4eb74a2516a24981b9064"
+    LLVM_COMMIT = "03730cdd3d10c5270fe436777a37d50b0838a3bf"
+    LLVM_SHA256 = "54d843249c75b200f7bf9b7947079fe16fa0b657c4aee4abdde4ac05a9cd5f84"
 
     tf_http_archive(
         name = name,

xla/service/elemental_ir_emitter.cc

@@ -86,8 +86,6 @@ using llvm_ir::SetToFirstInsertPoint;
 using xla::float8_fnuz_ir_emitter::EmitF8fnuzToFloating;
 using xla::float8_fnuz_ir_emitter::EmitFloatingToF8fnuz;
 
-namespace {
-
 absl::StatusOr<llvm::Value*> EmitReducePrecisionIR(
     PrimitiveType src_ty, llvm::Value* x, int64_t dest_exponent_bits,
     int64_t dest_mantissa_bits, bool quiet_nans, llvm::IRBuilderBase* b) {
@@ -231,6 +229,8 @@ absl::StatusOr<llvm::Value*> EmitReducePrecisionIR(
   return result;
 }
 
+namespace {
+
 template <int f8_exponent_bits>
 llvm::Value* handle_halfway_points_F16ToF8(llvm::Value* f16_abs_bits,
                                            llvm::Value* f8_bits,

xla/service/elemental_ir_emitter.h

@@ -352,6 +352,10 @@ class ElementalIrEmitterForTests : public ElementalIrEmitter {
   HloToElementGeneratorMap generator_map_;
 };
 
+absl::StatusOr<llvm::Value*> EmitReducePrecisionIR(
+    PrimitiveType src_ty, llvm::Value* x, int64_t dest_exponent_bits,
+    int64_t dest_mantissa_bits, bool quiet_nans, llvm::IRBuilderBase* b);
+
 }  // namespace xla
 
 #endif  // XLA_SERVICE_ELEMENTAL_IR_EMITTER_H_

xla/service/elemental_ir_emitter_test.cc

@@ -36,6 +36,7 @@ limitations under the License.
 #include "xla/literal_util.h"
 #include "xla/service/hlo_module_config.h"
 #include "xla/service/llvm_ir/ir_array.h"
+#include "xla/service/llvm_ir/llvm_util.h"
 #include "xla/test.h"
 #include "xla/tests/hlo_test_base.h"
 #include "xla/tests/test_macros.h"
@@ -48,6 +49,11 @@ namespace {
 
 using std::nullopt;
 
+struct EmitReducePrecisionIrTestCase {
+  float input;
+  std::string expected_res;
+};
+
 class ElementalIrEmitterExecutionTest : public HloTestBase {
  protected:
   void RunTest(const std::string& hlo_text, absl::Span<Literal* const> args) {
@@ -123,6 +129,192 @@ ENTRY main {
   RunTest(hlo_text, {&lhs, &rhs});
 }
 
+XLA_TEST_F(ElementalIrEmitterExecutionTest, EmitReducePrecisionIR_F16ToF8e5m2) {
+  llvm::LLVMContext llvm_context;
+  llvm::IRBuilder<> builder(llvm_context);
+  llvm::IRBuilderBase* b = &builder;
+  llvm::Type* f16_type = b->getHalfTy();
+
+  float inf = std::numeric_limits<float>::infinity();
+  float qnan = std::numeric_limits<float>::quiet_NaN();
+  float snan = std::numeric_limits<float>::signaling_NaN();
+
+  EmitReducePrecisionIrTestCase test_cases[] = {
+      // clang-format off
+      {0.0, "half 0xH0000"},
+      {0x1.0p-14, "half 0xH0400"},
+      {0.250, "half 0xH3400"},
+      {1.0, "half 0xH3C00"},
+      {0x1.2p0, "half 0xH3C00"},
+      {0x1.Cp15, "half 0xH7B00"},
+      {-0x1.Cp15, "half 0xHFB00"},
+      {0x1.Dp15, "half 0xH7B00"},
+      {0x1.Ep15, "half 0xH7C00"},
+      {0x1.0p16, "half 0xH7C00"},
+      {inf, "half 0xH7C00"},
+      {-inf, "half 0xHFC00"},
+      {qnan, "half 0xH7E00"},
+      {-qnan, "half 0xHFE00"},
+      {snan, "half 0xH7F00"},
+      {-snan, "half 0xHFF00"},
+      // clang-format on
+  };
+
+  for (auto tc : test_cases) {
+    llvm::Value* c0 = llvm::ConstantFP::get(f16_type, tc.input);
+
+    absl::StatusOr<llvm::Value*> f16_reduced_statusor = EmitReducePrecisionIR(
+        /*src_ty=*/F16, c0,
+        /*dest_exponent_bits=*/primitive_util::ExponentWidth(F8E5M2),
+        /*dest_mantissa_bits=*/primitive_util::SignificandWidth(F8E5M2) - 1,
+        /*quiet_nans=*/true, b);
+    CHECK(f16_reduced_statusor.ok());
+    llvm::Value* f16_reduced = f16_reduced_statusor.value();
+
+    std::string res = llvm_ir::DumpToString(f16_reduced);
+    EXPECT_EQ(res, tc.expected_res) << "Wrong result for input " << tc.input;
+  }
+}
+
+XLA_TEST_F(ElementalIrEmitterExecutionTest, EmitReducePrecisionIR_F16ToF8e4m3) {
+  llvm::LLVMContext llvm_context;
+  llvm::IRBuilder<> builder(llvm_context);
+  llvm::IRBuilderBase* b = &builder;
+  llvm::Type* f16_type = b->getHalfTy();
+
+  float inf = std::numeric_limits<float>::infinity();
+  float qnan = std::numeric_limits<float>::quiet_NaN();
+  float snan = std::numeric_limits<float>::signaling_NaN();
+
+  EmitReducePrecisionIrTestCase test_cases[] = {
+      // clang-format off
+      {0.0, "half 0xH0000"},
+      {0x1.0p-6, "half 0xH2400"},
+      {0.125, "half 0xH3000"},
+      {1.0, "half 0xH3C00"},
+      {0x1.1p0, "half 0xH3C00"},
+      {0x1.Ep7, "half 0xH5B80"},
+      {-0x1.Ep7, "half 0xHDB80"},
+      {0x1.E8p7, "half 0xH5B80"},
+      {0x1.Fp7, "half 0xH7C00"},
+      {0x1.0p8, "half 0xH7C00"},
+      {inf, "half 0xH7C00"},
+      {-inf, "half 0xHFC00"},
+      {qnan, "half 0xH7E00"},
+      {-qnan, "half 0xHFE00"},
+      {snan, "half 0xH7E00"},
+      {-snan, "half 0xHFE00"},
+      // clang-format on
+  };
+
+  for (auto tc : test_cases) {
+    llvm::Value* c0 = llvm::ConstantFP::get(f16_type, tc.input);
+
+    absl::StatusOr<llvm::Value*> f16_reduced_statusor = EmitReducePrecisionIR(
+        /*src_ty=*/F16, c0,
+        /*dest_exponent_bits=*/4,
+        /*dest_mantissa_bits=*/3,
+        /*quiet_nans=*/true, b);
+    CHECK(f16_reduced_statusor.ok());
+    llvm::Value* f16_reduced = f16_reduced_statusor.value();
+
+    std::string res = llvm_ir::DumpToString(f16_reduced);
+    EXPECT_EQ(res, tc.expected_res) << "Wrong result for input " << tc.input;
+  }
+}
+
+XLA_TEST_F(ElementalIrEmitterExecutionTest, EmitReducePrecisionIR_F16ToF8e3m4) {
+  llvm::LLVMContext llvm_context;
+  llvm::IRBuilder<> builder(llvm_context);
+  llvm::IRBuilderBase* b = &builder;
+  llvm::Type* f16_type = b->getHalfTy();
+
+  float inf = std::numeric_limits<float>::infinity();
+  float qnan = std::numeric_limits<float>::quiet_NaN();
+  float snan = std::numeric_limits<float>::signaling_NaN();
+
+  EmitReducePrecisionIrTestCase test_cases[] = {
+      // clang-format off
+      {0.0, "half 0xH0000"},
+      {0x1.0p-2, "half 0xH3400"},
+      {0.5, "half 0xH3800"},
+      {1.0, "half 0xH3C00"},
+      {0x1.08p0, "half 0xH3C00"},
+      {0x1.Fp3, "half 0xH4BC0"},
+      {-0x1.Fp3, "half 0xHCBC0"},
+      {0x1.F4p3, "half 0xH4BC0"},
+      {0x1.F8p3, "half 0xH7C00"},
+      {0x1.0p4, "half 0xH7C00"},
+      {inf, "half 0xH7C00"},
+      {-inf, "half 0xHFC00"},
+      {qnan, "half 0xH7E00"},
+      {-qnan, "half 0xHFE00"},
+      {snan, "half 0xH7E00"},
+      {-snan, "half 0xHFE00"},
+      // clang-format on
+  };
+
+  for (auto tc : test_cases) {
+    llvm::Value* c0 = llvm::ConstantFP::get(f16_type, tc.input);
+
+    absl::StatusOr<llvm::Value*> f16_reduced_statusor = EmitReducePrecisionIR(
+        /*src_ty=*/F16, c0,
+        /*dest_exponent_bits=*/3,
+        /*dest_mantissa_bits=*/4,
+        /*quiet_nans=*/true, b);
+    CHECK(f16_reduced_statusor.ok());
+    llvm::Value* f16_reduced = f16_reduced_statusor.value();
+
+    std::string res = llvm_ir::DumpToString(f16_reduced);
+    EXPECT_EQ(res, tc.expected_res) << "Wrong result for input " << tc.input;
+  }
+}
+
+XLA_TEST_F(ElementalIrEmitterExecutionTest,
+           EmitReducePrecisionIR_F16ToF8e4m3fn) {
+  llvm::LLVMContext llvm_context;
+  llvm::IRBuilder<> builder(llvm_context);
+  llvm::IRBuilderBase* b = &builder;
+  llvm::Type* f16_type = b->getHalfTy();
+
+  float inf = std::numeric_limits<float>::infinity();
+
+  EmitReducePrecisionIrTestCase test_cases[] = {
+      // clang-format off
+      {0.0, "half 0xH0000"},
+      {0x1.0p-6, "half 0xH2400"},
+      {0.125, "half 0xH3000"},
+      {1.0, "half 0xH3C00"},
+      {0x1.1p0, "half 0xH3C00"},
+      {0x1.Cp8, "half 0xH5F00"},
+      {-0x1.Cp8, "half 0xHDF00"},
+      {0x1.Dp8, "half 0xH5F00"},
+      {0x1.Ep8, "half 0xH5F80"},
+      {0x1.0p9, "half 0xH6000"},
+      {inf, "half 0xH7C00"},
+      {-inf, "half 0xHFC00"},
+      // clang-format on
+  };
+
+  for (auto tc : test_cases) {
+    llvm::Value* c0 = llvm::ConstantFP::get(f16_type, tc.input);
+
+    // Truncate the mantissa to 3 bits. ReducePrecision cannot deal with
+    // f8E4M3FN's NaN representations, so don't use ReducePrecision to handle
+    // exponent reduction.
+    absl::StatusOr<llvm::Value*> f16_reduced_statusor = EmitReducePrecisionIR(
+        /*src_ty=*/F16, c0,
+        /*dest_exponent_bits=*/5,
+        /*dest_mantissa_bits=*/3,
+        /*quiet_nans=*/false, b);
+    CHECK(f16_reduced_statusor.ok());
+    llvm::Value* f16_reduced = f16_reduced_statusor.value();
+
+    std::string res = llvm_ir::DumpToString(f16_reduced);
+    EXPECT_EQ(res, tc.expected_res) << "Wrong result for input " << tc.input;
+  }
+}
+
 XLA_TEST_F(ElementalIrEmitterExecutionTest, ScalarDotFusion) {
   const char* hlo_text = R"(
 HloModule ScalarDotFusion