[llvm] [LTO] Preserve module inline asm target properties for .lto_discard and symvers (PR #225130)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson updated https://github.com/llvm/llvm-project/pull/225130

>From ea291d0c0beb2b2e945c31fa84e11aef979fdc90 Mon Sep 17 00:00:00 2001
From: Alex Richardson <alexrichardson at google.com>
Date: Mon, 21 Sep 2026 23:42:19 -0700
Subject: [PATCH 1/2] [LTO] Preserve module inline asm target properties for
 .lto_discard and symvers

Previously, LTO::addRegularLTO() and IRLinker::run() called
prependModuleInlineAsm() and appendModuleInlineAsm() with a plain string when
synthesizing `.lto_discard` and imported `.symver` directives, creating a new
GlobalAsmFragment with empty TargetCPU and TargetFeatures instead of preserving
the existing module inline asm's properties. Copy the front fragment's Props so
these synthesized directives are merged into the module's inline asm with the
same target features.

This commit was created with the help of AI tools
---
 cross-project-tests/riscv/lto-inline-asm-abi.c | 7 ++-----
 llvm/lib/LTO/LTO.cpp                           | 2 +-
 llvm/lib/Linker/IRMover.cpp                    | 3 ++-
 llvm/test/LTO/RISCV/module-asm.ll              | 5 +----
 4 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/cross-project-tests/riscv/lto-inline-asm-abi.c b/cross-project-tests/riscv/lto-inline-asm-abi.c
index e89e1e4f0687d..883244f1854f7 100644
--- a/cross-project-tests/riscv/lto-inline-asm-abi.c
+++ b/cross-project-tests/riscv/lto-inline-asm-abi.c
@@ -22,15 +22,12 @@
 // RUN: llvm-objdump -d --show-all-symbols --no-show-raw-insn %t.thin.so | FileCheck %s --check-prefix=DISASM
 // RUN: llvm-objdump -t %t.thin.so | FileCheck %s --check-prefix=SYMS --implicit-check-not='\$x'
 //
-/// TODO: LTO::addRegularLTO and IRLinker::run drop target_features and
-/// target_cpu when synthesizing .lto_discard and imported .symver directives.
-// REGULAR-IR:      module asm{{$}}
+// REGULAR-IR:      module asm(target_features: "+64bit,{{.*}}", target_cpu: "generic-rv64")
 // REGULAR-IR-NEXT:     ".lto_discard "
-// REGULAR-IR-NEXT: module asm(target_features: "+64bit,{{.*}}", target_cpu: "generic-rv64")
 // REGULAR-IR-NEXT:     "nop"
 // REGULAR-IR-NEXT:     ".symver symver_fn, symver_fn at VER_1.0"
 //
-// THIN-IR:      module asm{{$}}
+// THIN-IR:      module asm(target_features: "+64bit,{{.*}}", target_cpu: "generic-rv64")
 // THIN-IR-NEXT:     ".symver symver_fn, symver_fn at VER_1.0"
 //
 // FLAGS:      Flags [ (0x5)
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 4594c52fb5f6e..e307b7f1c16e8 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1129,7 +1129,7 @@ LTO::addRegularLTO(InputFile &Input, ArrayRef<SymbolResolution> InputRes,
       NewIA += " " + llvm::join(NonPrevailingAsmSymbols, ", ");
     }
     NewIA += "\n";
-    M.prependModuleInlineAsm(NewIA);
+    M.prependModuleInlineAsm({NewIA, M.getModuleInlineAsm().front().Props});
   }
 
   assert(MsymI == MsymE);
diff --git a/llvm/lib/Linker/IRMover.cpp b/llvm/lib/Linker/IRMover.cpp
index 3b72b412d0b2e..080ba6d542f71 100644
--- a/llvm/lib/Linker/IRMover.cpp
+++ b/llvm/lib/Linker/IRMover.cpp
@@ -1576,7 +1576,8 @@ Error IRLinker::run() {
         S += Name;
         S += ", ";
         S += Alias;
-        DstM.appendModuleInlineAsm(std::string(S));
+        DstM.appendModuleInlineAsm(
+            {std::string(S), SrcM->getModuleInlineAsm().front().Props});
       }
     });
   }
diff --git a/llvm/test/LTO/RISCV/module-asm.ll b/llvm/test/LTO/RISCV/module-asm.ll
index e213ec14a2a58..f27943f5457ac 100644
--- a/llvm/test/LTO/RISCV/module-asm.ll
+++ b/llvm/test/LTO/RISCV/module-asm.ll
@@ -7,11 +7,8 @@
 
 ; NM: T func
 
-;; TODO: LTO::addRegularLTO prepends ".lto_discard" without preserving the
-;; existing module inline asm's TargetCPU and TargetFeatures.
-; IR:      module asm
+; IR:      module asm(target_features: "+d")
 ; IR-NEXT:     ".lto_discard"
-; IR-NEXT: module asm(target_features: "+d")
 ; IR-NEXT:     ".globl func"
 ; IR-NEXT:     "func:"
 ; IR-NEXT:     "fld f0, 0(sp)"

>From 7579da8c326084f20a3fc6df8df7dd5b1302f4b4 Mon Sep 17 00:00:00 2001
From: Alex Richardson <alexrichardson at google.com>
Date: Tue, 22 Sep 2026 22:52:24 -0700
Subject: [PATCH 2/2] address feedback

---
 llvm/lib/Linker/IRMover.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/Linker/IRMover.cpp b/llvm/lib/Linker/IRMover.cpp
index 080ba6d542f71..d96c5d18a0ae3 100644
--- a/llvm/lib/Linker/IRMover.cpp
+++ b/llvm/lib/Linker/IRMover.cpp
@@ -1577,7 +1577,7 @@ Error IRLinker::run() {
         S += ", ";
         S += Alias;
         DstM.appendModuleInlineAsm(
-            {std::string(S), SrcM->getModuleInlineAsm().front().Props});
+            {std::string(S), SrcM->getModuleInlineAsm().back().Props});
       }
     });
   }