[libc-commits] [libc] [libc] Save one instruction on ARM (PR #181515)

[via libc-commits]

https://github.com/SiliconA-Z created https://github.com/llvm/llvm-project/pull/181515

For assembler functions, doing them as best as possible is paramount. Save sp in ARM, restore sp in ARM.

>From 97df66ddb1c5b62838d69ca9af35e023536ce6c3 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Sat, 14 Feb 2026 17:50:10 -0500
Subject: [PATCH] Save one instruction on ARM

For assembler functions, doing them as best as possible is paramount.
---
 libc/src/setjmp/arm/longjmp.cpp | 19 +++++++++++++++++--
 libc/src/setjmp/arm/setjmp.cpp  | 17 ++++++++++++++++-
 2 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/libc/src/setjmp/arm/longjmp.cpp b/libc/src/setjmp/arm/longjmp.cpp
index 623ca8fc77be6..dec47aa20b6d1 100644
--- a/libc/src/setjmp/arm/longjmp.cpp
+++ b/libc/src/setjmp/arm/longjmp.cpp
@@ -49,7 +49,7 @@ namespace LIBC_NAMESPACE_DECL {
       bx lr)");
 }
 
-#else // Thumb2 or ARM
+#elif defined(__thumb__) && __ARM_ARCH_ISA_THUMB == 2
 
 // TODO(https://github.com/llvm/llvm-project/issues/94061): fp registers
 // (d0-d16)
@@ -59,7 +59,6 @@ namespace LIBC_NAMESPACE_DECL {
       # While sp may appear in a register list for ARM mode, it may not for
       # Thumb2 mode. Just load the previous value of sp into r12 then move it
       # into sp, so that this code is portable between ARM and Thumb2.
-
       ldm r0, {r4-r12, lr}
       mov sp, r12
 
@@ -70,6 +69,22 @@ namespace LIBC_NAMESPACE_DECL {
       bx lr)");
 }
 
+#else // ARM
+
+// TODO(https://github.com/llvm/llvm-project/issues/94061): fp registers
+// (d0-d16)
+// TODO(https://github.com/llvm/llvm-project/issues/94062): pac+bti
+[[gnu::naked]] LLVM_LIBC_FUNCTION(void, longjmp, (jmp_buf buf, int val)) {
+  asm(R"(
+      # Store r4, r5, r6, r7, r8, r9, r10, r11, sp, and lr into buf.
+      ldm r0, {r4-r11, sp, lr}
+
+      # return val ?: 1;
+      movs r0, r1
+      moveq r0, #1
+      bx lr)");
+}
+
 #endif
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/setjmp/arm/setjmp.cpp b/libc/src/setjmp/arm/setjmp.cpp
index 891ac3016c050..a4ba7949c5227 100644
--- a/libc/src/setjmp/arm/setjmp.cpp
+++ b/libc/src/setjmp/arm/setjmp.cpp
@@ -39,7 +39,7 @@ namespace LIBC_NAMESPACE_DECL {
       bx lr)");
 }
 
-#else // Thumb2 or ARM
+#elif defined(__thumb__) && __ARM_ARCH_ISA_THUMB == 2
 
 // TODO(https://github.com/llvm/llvm-project/issues/94061): fp registers
 // (d0-d16)
@@ -59,6 +59,21 @@ namespace LIBC_NAMESPACE_DECL {
       bx lr)");
 }
 
+#else // ARM
+
+// TODO(https://github.com/llvm/llvm-project/issues/94061): fp registers
+// (d0-d16)
+// TODO(https://github.com/llvm/llvm-project/issues/94062): pac+bti
+[[gnu::naked]] LLVM_LIBC_FUNCTION(int, setjmp, (jmp_buf buf)) {
+  asm(R"(
+      # Store r4, r5, r6, r7, r8, r9, r10, r11, sp, and lr into buf.
+      stm r0, {r4-r11, sp, lr}
+
+      # Return zero.
+      mov r0, #0
+      bx lr)");
+}
+
 #endif
 
 } // namespace LIBC_NAMESPACE_DECL