[clang] [Clang][Driver][ARM] Forward `-Os` and `-Oz` as multilib flags (PR #149819)

[Victor Campos via cfe-commits]

https://github.com/vhscampos created https://github.com/llvm/llvm-project/pull/149819

Pass along `-Os` and `-Oz` as multilib flags under ARM and AArch64 so that they can be used as criteria for multilib selection.

>From 108e27d18914cf91aa7490374efad531b2011763 Mon Sep 17 00:00:00 2001
From: Victor Campos <victor.campos at arm.com>
Date: Fri, 18 Jul 2025 17:08:35 +0100
Subject: [PATCH] [Clang][Driver][ARM] Forward `-Os` and `-Oz` as multilib
 flags

Pass along `-Os` and `-Oz` as multilib flags under ARM and AArch64 so
that they can be used as criteria for multilib selection.
---
 clang/lib/Driver/ToolChain.cpp                | 25 +++++++++++++++++++
 .../test/Driver/print-multi-selection-flags.c | 17 +++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 481f575518b93..8c443f03f2b06 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -255,6 +255,18 @@ static void getAArch64MultilibFlags(const Driver &D,
     Result.push_back(ABIArg->getAsString(Args));
   }
 
+  if (const Arg *A = Args.getLastArg(options::OPT_O_Group);
+      A && A->getOption().matches(options::OPT_O)) {
+    switch (A->getValue()[0]) {
+    case 's':
+      Result.push_back("-Os");
+      break;
+    case 'z':
+      Result.push_back("-Oz");
+      break;
+    }
+  }
+
   processMultilibCustomFlags(Result, Args);
 }
 
@@ -332,6 +344,19 @@ static void getARMMultilibFlags(const Driver &D, const llvm::Triple &Triple,
     if (Endian->getOption().matches(options::OPT_mbig_endian))
       Result.push_back(Endian->getAsString(Args));
   }
+
+  if (const Arg *A = Args.getLastArg(options::OPT_O_Group);
+      A && A->getOption().matches(options::OPT_O)) {
+    switch (A->getValue()[0]) {
+    case 's':
+      Result.push_back("-Os");
+      break;
+    case 'z':
+      Result.push_back("-Oz");
+      break;
+    }
+  }
+
   processMultilibCustomFlags(Result, Args);
 }
 
diff --git a/clang/test/Driver/print-multi-selection-flags.c b/clang/test/Driver/print-multi-selection-flags.c
index 8cf8f04bb6b48..b1a0a29ec4180 100644
--- a/clang/test/Driver/print-multi-selection-flags.c
+++ b/clang/test/Driver/print-multi-selection-flags.c
@@ -126,3 +126,20 @@
 // CHECK-PIE1: -fpie
 // CHECK-ROPI: -fropi
 // CHECK-RWPI: -frwpi
+
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -Os | FileCheck --check-prefix=CHECK-OPT-OS %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -Oz | FileCheck --check-prefix=CHECK-OPT-OZ %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a     | FileCheck --check-prefix=CHECK-OPT %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -O1 | FileCheck --check-prefix=CHECK-OPT %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -O2 | FileCheck --check-prefix=CHECK-OPT %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -O3 | FileCheck --check-prefix=CHECK-OPT %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-eabi -Os           | FileCheck --check-prefix=CHECK-OPT-OS %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-eabi -Oz           | FileCheck --check-prefix=CHECK-OPT-OZ %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-eabi               | FileCheck --check-prefix=CHECK-OPT %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-eabi -O1           | FileCheck --check-prefix=CHECK-OPT %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-eabi -O2           | FileCheck --check-prefix=CHECK-OPT %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-eabi -O3           | FileCheck --check-prefix=CHECK-OPT %s
+// CHECK-OPT-OZ: -Oz
+// CHECK-OPT-OS: -Os
+// CHECK-OPT-NOT: -Oz
+// CHECK-OPT-NOT: -Os