File 2203-Enhance-the-mov_imm-helper.patch of Package erlang

Overview Repositories Revisions Requests Users Attributes Meta

File 2203-Enhance-the-mov_imm-helper.patch of Package erlang (Revision 33ddd6d11afd5bd1cc05a48b3cb9b6d8)

Currently displaying revision 33ddd6d11afd5bd1cc05a48b3cb9b6d8 , Show latest

From 2ac5f27a4115b5c0fcad0e6b3029e679e4c00afd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Sat, 9 Oct 2021 10:31:27 +0200
Subject: [PATCH 3/6] Enhance the mov_imm() helper

Generate a shorter instruction for unsigned immediate values that
fit in 32 bits.
---
 erts/emulator/beam/jit/x86/beam_asm.hpp     | 15 ++++++++++++++-
 erts/emulator/beam/jit/x86/instr_common.cpp |  7 ++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/erts/emulator/beam/jit/x86/beam_asm.hpp b/erts/emulator/beam/jit/x86/beam_asm.hpp
index dee1edebb5..5e83c7e83c 100644
--- a/erts/emulator/beam/jit/x86/beam_asm.hpp
+++ b/erts/emulator/beam/jit/x86/beam_asm.hpp
@@ -795,7 +795,20 @@ protected:
     void mov_imm(x86::Gp to, T value) {
         static_assert(std::is_integral<T>::value || std::is_pointer<T>::value);
         if (value) {
-            a.mov(to, imm(value));
+            /* Generate the shortest instruction to set the register to an
+             * immediate.
+             *
+             *   48 c7 c0 2a 00 00 00    mov    rax, 42
+             *   b8 2a 00 00 00          mov    eax, 42
+             *
+             *   49 c7 c0 2a 00 00 00    mov    r8, 42
+             *   41 b8 2a 00 00 00       mov    r8d, 42
+             */
+            if (Support::isUInt32((Uint)value)) {
+                a.mov(to.r32(), imm(value));
+            } else {
+                a.mov(to, imm(value));
+            }
         } else {
             /*
              * Generate the shortest instruction to set the register to zero.
diff --git a/erts/emulator/beam/jit/x86/instr_common.cpp b/erts/emulator/beam/jit/x86/instr_common.cpp
index e0dd4d792b..8d046db40e 100644
--- a/erts/emulator/beam/jit/x86/instr_common.cpp
+++ b/erts/emulator/beam/jit/x86/instr_common.cpp
@@ -25,10 +25,15 @@
  * one byte shorter than instructions that use 64-bits registers
  * (e.g. rax). This does not apply to registers r8-r15 because they'll
  * always need a rex prefix. The `and`, `or`, and `cmp` instructions
- * are even shorter than operating on the RETb (al) register. The
+ * are even shorter when operating on the RETb (al) register. The
  * `test` instruction with an immediate second operand is shorter
  * when operating on an 8-bit register.
  *
+ * When loading an immediate value to a register, storing to the
+ * 32-bit register in one or two bytes shorter than storing to
+ * the corresponding 64-bit register. The mov_imm() helper
+ * will automatically choose the shortest instruction.
+ *
  * On both Unix and Windows, instructions can be shortened by using
  * RETd, ARG1d, or ARG2d instead of RET, ARG1, or ARG2, respectively.
  * On Unix, but not on Windows, ARG3d and ARG4d will also result in
-- 
2.31.1

Places

File 2203-Enhance-the-mov_imm-helper.patch of Package erlang (Revision 33ddd6d11afd5bd1cc05a48b3cb9b6d8)

Places