[clang] clang: Emit "float-abi" module flag (PR #212985)

[Matt Arsenault via cfe-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/212985

Emit the new module flag if it differs from the triple's
default.

Co-authored-by: Claude (Claude-Opus-4.8) <noreply at anthropic.com>

>From 15b5e5c27380c6279c1a3950a1e3434c1ea4bafe Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Mon, 20 Jul 2026 14:04:43 +0200
Subject: [PATCH] clang: Emit "float-abi" module flag

Emit the new module flag if it differs from the triple's
default.

Co-authored-by: Claude (Claude-Opus-4.8) <noreply at anthropic.com>
---
 clang/lib/CodeGen/CodeGenModule.cpp     | 15 ++++++++++++
 clang/test/CodeGen/arm-float-abi-flag.c | 32 +++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 clang/test/CodeGen/arm-float-abi-flag.c

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index e7c1d182fd20d..b0be2a2fc0d96 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1380,6 +1380,21 @@ void CodeGenModule::Release() {
     getModule().addModuleFlag(llvm::Module::Error, "wchar_size",
                               static_cast<uint32_t>(WCharWidth));
 
+  // Record the floating-point ABI as a module flag when it differs from the
+  // target default. softfp collapses to soft.
+  llvm::FloatABI::ABIType FloatABI =
+      llvm::StringSwitch<llvm::FloatABI::ABIType>(CodeGenOpts.FloatABI)
+          .Cases({"soft", "softfp"}, llvm::FloatABI::Soft)
+          .Case("hard", llvm::FloatABI::Hard)
+          .Default(llvm::FloatABI::Default);
+  if (FloatABI != llvm::FloatABI::Default &&
+      FloatABI != getTriple().getDefaultFloatABI()) {
+    getModule().addModuleFlag(
+        llvm::Module::Error, "float-abi",
+        llvm::MDString::get(getLLVMContext(),
+                            llvm::FloatABI::getABITypeName(FloatABI)));
+  }
+
   if (getTriple().isOSzOS()) {
     getModule().addModuleFlag(llvm::Module::Warning,
                               "zos_product_major_version",
diff --git a/clang/test/CodeGen/arm-float-abi-flag.c b/clang/test/CodeGen/arm-float-abi-flag.c
new file mode 100644
index 0000000000000..dcbe4ab2a82ab
--- /dev/null
+++ b/clang/test/CodeGen/arm-float-abi-flag.c
@@ -0,0 +1,32 @@
+// Check that clang emits the "float-abi" module flag only when the resolved
+// floating-point ABI differs from the target default.
+
+// Default (soft) ABI on a soft-default triple: no flag.
+// RUN: %clang_cc1 -triple arm-none-none-eabi -emit-llvm -o - %s \
+// RUN:   | FileCheck %s --check-prefix=NONE
+
+// Explicit hard on a soft-default triple: flag emitted.
+// RUN: %clang_cc1 -triple arm-none-none-eabi -mfloat-abi hard -emit-llvm -o - %s \
+// RUN:   | FileCheck %s --check-prefix=HARD
+
+// Explicit soft on a soft-default triple: matches default, no flag.
+// RUN: %clang_cc1 -triple arm-none-none-eabi -mfloat-abi soft -emit-llvm -o - %s \
+// RUN:   | FileCheck %s --check-prefix=NONE
+
+// Default (hard) ABI on a hard-default triple: no flag.
+// RUN: %clang_cc1 -triple arm-none-none-eabihf -emit-llvm -o - %s \
+// RUN:   | FileCheck %s --check-prefix=NONE
+
+// Explicit soft on a hard-default triple: flag emitted.
+// RUN: %clang_cc1 -triple arm-none-none-eabihf -mfloat-abi soft -emit-llvm -o - %s \
+// RUN:   | FileCheck %s --check-prefix=SOFT
+
+// softfp collapses to soft: on a hard-default triple, flag emitted as soft.
+// RUN: %clang_cc1 -triple arm-none-none-eabihf -mfloat-abi softfp -emit-llvm -o - %s \
+// RUN:   | FileCheck %s --check-prefix=SOFT
+
+void f(void) {}
+
+// NONE-NOT: !"float-abi"
+// HARD: !{i32 1, !"float-abi", !"hard"}
+// SOFT: !{i32 1, !"float-abi", !"soft"}