From ad48a4fc321adc58cd2843da64b2e206441c7e96 Mon Sep 17 00:00:00 2001 From: Cameron Zwarich Date: Mon, 21 Feb 2011 01:29:32 +0000 Subject: [PATCH] A lo/hi mul has higher latency than an imul r,ri, e.g. 5 cycles compared to 3 on Core 2 and Nehalem, so the code we generate is better than GCC's here. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126100 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/X86/README.txt | 35 ----------------------------------- 1 file changed, 35 deletions(-) diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index ed3bff150bc..1e1660dbca0 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -1878,38 +1878,3 @@ _add32carry: ret //===---------------------------------------------------------------------===// - -This: -char t(char c) { - return c/3; -} - -Compiles to: $clang t.c -S -o - -O3 -mkernel -fomit-frame-pointer - -_t: ## @t - movslq %edi, %rax - imulq $1431655766, %rax, %rax ## imm = 0x55555556 - movq %rax, %rcx - shrq $63, %rcx - shrq $32, %rax - addl %ecx, %eax - movsbl %al, %eax - ret - -GCC gets: - -_t: - movl $86, %eax - imulb %dil - shrw $8, %ax - sarb $7, %dil - subb %dil, %al - movsbl %al,%eax - ret - -which is nicer. This also happens for int, not just char. - -//===---------------------------------------------------------------------===// - - -