[clang] [Clang] Honor '#pragma STDC FENV_ROUND' in __builtin_store_half/halff (PR #173821)

[Wenju He via cfe-commits]

https://github.com/wenju-he updated https://github.com/llvm/llvm-project/pull/173821

>From 84478d7b427d32c5b9f24fc1f2b8e1d957563a96 Mon Sep 17 00:00:00 2001
From: Wenju He <wenju.he at intel.com>
Date: Mon, 29 Dec 2025 06:19:00 +0100
Subject: [PATCH 1/2] [Clang] Honor '#pragma STDC FENV_ROUND' in
 __builtin_store_half/halff

Before this change, constrained fptrunc for __builtin_store_half/halff
always used round.tonearest, ignoring the active pragma STDC FENV_ROUND.

This PR guards builtin emission with CGFPOptionsRAII so the current
rounding mode is propagated to the generated constrained intrinsic.
---
 clang/lib/CodeGen/CGBuiltin.cpp               |  1 +
 ...builtin-store-half-rounding-constrained.cl | 21 +++++++++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index d3abf6d2a1f2d..0f9bed130a3b0 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -6199,6 +6199,7 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   }
   case Builtin::BI__builtin_store_half:
   case Builtin::BI__builtin_store_halff: {
+    CodeGenFunction::CGFPOptionsRAII FPOptsRAII(*this, E);
     Value *Val = EmitScalarExpr(E->getArg(0));
     Address Address = EmitPointerWithAlignment(E->getArg(1));
     Value *HalfVal = Builder.CreateFPTrunc(Val, Builder.getHalfTy());
diff --git a/clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl b/clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl
new file mode 100644
index 0000000000000..a9334d22fe05f
--- /dev/null
+++ b/clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 %s -cl-std=cl3.0 -emit-llvm -o - -triple x86_64-unknown-unknown | FileCheck %s
+
+// CHECK-LABEL: @test_store_float(
+// CHECK:         [[TMP0:%.*]] = tail call half @llvm.experimental.constrained.fptrunc.f16.f32(float {{.*}}, metadata !"round.upward", metadata !"fpexcept.ignore")
+// CHECK-NEXT:    store half [[TMP0]], ptr {{.*}}, align 2
+// CHECK-NEXT:    ret void
+//
+__kernel void test_store_float(float foo, __global half* bar) {
+  #pragma STDC FENV_ROUND FE_UPWARD
+  __builtin_store_halff(foo, bar);
+}
+
+// CHECK-LABEL: @test_store_double(
+// CHECK:         [[TMP0:%.*]] = tail call half @llvm.experimental.constrained.fptrunc.f16.f64(double {{.*}}, metadata !"round.downward", metadata !"fpexcept.ignore")
+// CHECK-NEXT:    store half [[TMP0]], ptr {{.*}}, align 2
+// CHECK-NEXT:    ret void
+//
+__kernel void test_store_double(double foo, __global half* bar) {
+  #pragma STDC FENV_ROUND FE_DOWNWARD
+  __builtin_store_half(foo, bar);
+}

>From 5e6e9e30828888cba97010127e796364c245d238 Mon Sep 17 00:00:00 2001
From: Wenju He <wenju.he at intel.com>
Date: Sun, 4 Jan 2026 05:55:40 +0100
Subject: [PATCH 2/2] add -disable-llvm-passes

---
 .../builtin-store-half-rounding-constrained.cl              | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl b/clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl
index a9334d22fe05f..ba3b3165e325a 100644
--- a/clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl
+++ b/clang/test/CodeGenOpenCL/builtin-store-half-rounding-constrained.cl
@@ -1,7 +1,7 @@
-// RUN: %clang_cc1 %s -cl-std=cl3.0 -emit-llvm -o - -triple x86_64-unknown-unknown | FileCheck %s
+// RUN: %clang_cc1 %s -cl-std=cl3.0 -triple x86_64-unknown-unknown -disable-llvm-passes -emit-llvm -o - | FileCheck %s
 
 // CHECK-LABEL: @test_store_float(
-// CHECK:         [[TMP0:%.*]] = tail call half @llvm.experimental.constrained.fptrunc.f16.f32(float {{.*}}, metadata !"round.upward", metadata !"fpexcept.ignore")
+// CHECK:         [[TMP0:%.*]] = call half @llvm.experimental.constrained.fptrunc.f16.f32(float {{.*}}, metadata !"round.upward", metadata !"fpexcept.ignore")
 // CHECK-NEXT:    store half [[TMP0]], ptr {{.*}}, align 2
 // CHECK-NEXT:    ret void
 //
@@ -11,7 +11,7 @@ __kernel void test_store_float(float foo, __global half* bar) {
 }
 
 // CHECK-LABEL: @test_store_double(
-// CHECK:         [[TMP0:%.*]] = tail call half @llvm.experimental.constrained.fptrunc.f16.f64(double {{.*}}, metadata !"round.downward", metadata !"fpexcept.ignore")
+// CHECK:         [[TMP0:%.*]] = call half @llvm.experimental.constrained.fptrunc.f16.f64(double {{.*}}, metadata !"round.downward", metadata !"fpexcept.ignore")
 // CHECK-NEXT:    store half [[TMP0]], ptr {{.*}}, align 2
 // CHECK-NEXT:    ret void
 //