1 files changed, 100 insertions, 0 deletions
diff --git a/vendor/compiler_builtins/src/mem/x86_64.rs b/vendor/compiler_builtins/src/mem/x86_64.rs
new file mode 100644
index 000000000..a7ab6f605
--- /dev/null
+++ b/vendor/compiler_builtins/src/mem/x86_64.rs
@@ -0,0 +1,100 @@
+// On most modern Intel and AMD processors, "rep movsq" and "rep stosq" have
+// been enhanced to perform better than an simple qword loop, making them ideal
+// for implementing memcpy/memset. Note that "rep cmps" has received no such
+// enhancement, so it is not used to implement memcmp.
+//
+// On certain recent Intel processors, "rep movsb" and "rep stosb" have been
+// further enhanced to automatically select the best microarchitectural
+// implementation based on length and alignment. See the following features from
+// the "Intel® 64 and IA-32 Architectures Optimization Reference Manual":
+//  - ERMSB - Enhanced REP MOVSB and STOSB (Ivy Bridge and later)
+//  - FSRM - Fast Short REP MOV (Ice Lake and later)
+//  - Fast Zero-Length MOVSB (On no current hardware)
+//  - Fast Short STOSB (On no current hardware)
+//
+// To simplify things, we switch to using the byte-based variants if the "ermsb"
+// feature is present at compile-time. We don't bother detecting other features.
+// Note that ERMSB does not enhance the backwards (DF=1) "rep movsb".
+
+#[inline(always)]
+#[cfg(target_feature = "ermsb")]
+pub unsafe fn copy_forward(dest: *mut u8, src: *const u8, count: usize) {
+    // FIXME: Use the Intel syntax once we drop LLVM 9 support on rust-lang/rust.
+    core::arch::asm!(
+        "repe movsb (%rsi), (%rdi)",
+        inout("rcx") count => _,
+        inout("rdi") dest => _,
+        inout("rsi") src => _,
+        options(att_syntax, nostack, preserves_flags)
+    );
+}
+
+#[inline(always)]
+#[cfg(not(target_feature = "ermsb"))]
+pub unsafe fn copy_forward(dest: *mut u8, src: *const u8, count: usize) {
+    let qword_count = count >> 3;
+    let byte_count = count & 0b111;
+    // FIXME: Use the Intel syntax once we drop LLVM 9 support on rust-lang/rust.
+    core::arch::asm!(
+        "repe movsq (%rsi), (%rdi)",
+        "mov {byte_count:e}, %ecx",
+        "repe movsb (%rsi), (%rdi)",
+        byte_count = in(reg) byte_count,
+        inout("rcx") qword_count => _,
+        inout("rdi") dest => _,
+        inout("rsi") src => _,
+        options(att_syntax, nostack, preserves_flags)
+    );
+}
+
+#[inline(always)]
+pub unsafe fn copy_backward(dest: *mut u8, src: *const u8, count: usize) {
+    let qword_count = count >> 3;
+    let byte_count = count & 0b111;
+    // FIXME: Use the Intel syntax once we drop LLVM 9 support on rust-lang/rust.
+    core::arch::asm!(
+        "std",
+        "repe movsq (%rsi), (%rdi)",
+        "movl {byte_count:e}, %ecx",
+        "addq $7, %rdi",
+        "addq $7, %rsi",
+        "repe movsb (%rsi), (%rdi)",
+        "cld",
+        byte_count = in(reg) byte_count,
+        inout("rcx") qword_count => _,
+        inout("rdi") dest.add(count).wrapping_sub(8) => _,
+        inout("rsi") src.add(count).wrapping_sub(8) => _,
+        options(att_syntax, nostack)
+    );
+}
+
+#[inline(always)]
+#[cfg(target_feature = "ermsb")]
+pub unsafe fn set_bytes(dest: *mut u8, c: u8, count: usize) {
+    // FIXME: Use the Intel syntax once we drop LLVM 9 support on rust-lang/rust.
+    core::arch::asm!(
+        "repe stosb %al, (%rdi)",
+        inout("rcx") count => _,
+        inout("rdi") dest => _,
+        inout("al") c => _,
+        options(att_syntax, nostack, preserves_flags)
+    )
+}
+
+#[inline(always)]
+#[cfg(not(target_feature = "ermsb"))]
+pub unsafe fn set_bytes(dest: *mut u8, c: u8, count: usize) {
+    let qword_count = count >> 3;
+    let byte_count = count & 0b111;
+    // FIXME: Use the Intel syntax once we drop LLVM 9 support on rust-lang/rust.
+    core::arch::asm!(
+        "repe stosq %rax, (%rdi)",
+        "mov {byte_count:e}, %ecx",
+        "repe stosb %al, (%rdi)",
+        byte_count = in(reg) byte_count,
+        inout("rcx") qword_count => _,
+        inout("rdi") dest => _,
+        in("rax") (c as u64) * 0x0101010101010101,
+        options(att_syntax, nostack, preserves_flags)
+    );
+}