[clang] Refine multilib selection to handle alignment based on architecture features. (PR #134099)

[Simi Pallipurath via cfe-commits]

https://github.com/simpal01 created https://github.com/llvm/llvm-project/pull/134099

Update the multilib selection logic to bypass the alignment option based on each architecture’s feature set, rather than relying on command-line options.

Previously, alignment option was bypassed only when -mno-unaligned-access was explicitly specified on the command line. This change makes the selection more robust and architecture aware.

>From 7f6302053575732f633c69bbf55f2624da1e8bf4 Mon Sep 17 00:00:00 2001
From: Simi Pallipurath <simi.pallipurath at arm.com>
Date: Wed, 2 Apr 2025 12:35:16 +0100
Subject: [PATCH] Refine multilib selection to handle alignment based on
 architecture features.
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

Update the multilib selection logic to bypass the
alignment option based on each architecture’s
feature set, rather than relying solely on command-line
options.

Previously, alignment option was bypassed only when
-mno-unaligned-access was explicitly specified on the
commandline. This change makes the selection more robust
and architecture aware.
---
 clang/lib/Driver/ToolChain.cpp                | 24 +++++++++----------
 .../test/Driver/print-multi-selection-flags.c |  6 +++++
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 8a922b283daf5..476026f82b32b 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -239,12 +239,12 @@ static void getAArch64MultilibFlags(const Driver &D,
     Result.push_back(BranchProtectionArg->getAsString(Args));
   }
 
-  if (Arg *AlignArg = Args.getLastArg(
-          options::OPT_mstrict_align, options::OPT_mno_strict_align,
-          options::OPT_mno_unaligned_access, options::OPT_munaligned_access)) {
-    if (AlignArg->getOption().matches(options::OPT_mstrict_align) ||
-        AlignArg->getOption().matches(options::OPT_mno_unaligned_access))
-      Result.push_back(AlignArg->getAsString(Args));
+  if (FeatureSet.contains("+strict-align")) {
+    Result.push_back("-mno-unaligned-access");
+    Result.push_back("-mstrict-align");
+  } else {
+    Result.push_back("-munaligned-access");
+    Result.push_back("-mno-strict-align");
   }
 
   if (Arg *Endian = Args.getLastArg(options::OPT_mbig_endian,
@@ -313,12 +313,12 @@ static void getARMMultilibFlags(const Driver &D,
     Result.push_back(BranchProtectionArg->getAsString(Args));
   }
 
-  if (Arg *AlignArg = Args.getLastArg(
-          options::OPT_mstrict_align, options::OPT_mno_strict_align,
-          options::OPT_mno_unaligned_access, options::OPT_munaligned_access)) {
-    if (AlignArg->getOption().matches(options::OPT_mstrict_align) ||
-        AlignArg->getOption().matches(options::OPT_mno_unaligned_access))
-      Result.push_back(AlignArg->getAsString(Args));
+  if (FeatureSet.contains("+strict-align")) {
+    Result.push_back("-mno-unaligned-access");
+    Result.push_back("-mstrict-align");
+  } else {
+    Result.push_back("-munaligned-access");
+    Result.push_back("-mno-strict-align");
   }
 
   if (Arg *Endian = Args.getLastArg(options::OPT_mbig_endian,
diff --git a/clang/test/Driver/print-multi-selection-flags.c b/clang/test/Driver/print-multi-selection-flags.c
index 5a35ae374f011..b21c2d11c1009 100644
--- a/clang/test/Driver/print-multi-selection-flags.c
+++ b/clang/test/Driver/print-multi-selection-flags.c
@@ -69,9 +69,15 @@
 // CHECK-BRANCH-PROTECTION: -mbranch-protection=standard
 
 // RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -mno-unaligned-access | FileCheck --check-prefix=CHECK-NO-UNALIGNED-ACCESS %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi | FileCheck --check-prefix=CHECK-NO-UNALIGNED-ACCESS %s
 // RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-elf -mno-unaligned-access | FileCheck --check-prefix=CHECK-NO-UNALIGNED-ACCESS %s
 // CHECK-NO-UNALIGNED-ACCESS: -mno-unaligned-access
 
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -munaligned-access | FileCheck --check-prefix=CHECK-UNALIGNED-ACCESS %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-elf | FileCheck --check-prefix=CHECK-UNALIGNED-ACCESS %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-elf -munaligned-access | FileCheck --check-prefix=CHECK-UNALIGNED-ACCESS %s
+// CHECK-UNALIGNED-ACCESS: -munaligned-access
+
 // RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -mbig-endian | FileCheck --check-prefix=CHECK-BIG-ENDIAN %s
 // RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=aarch64-none-elf -mbig-endian | FileCheck --check-prefix=CHECK-BIG-ENDIAN %s
 // CHECK-BIG-ENDIAN: -mbig-endian