mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2025-02-01 13:11:39 +01:00
0b5293684d
Summary: These changes cover the PR#31399. Now the ffs(x) function is lowered to (x != 0) ? llvm.cttz(x) + 1 : 0 and it corresponds to the following llvm code: %cnt = tail call i32 @llvm.cttz.i32(i32 %v, i1 true) %tobool = icmp eq i32 %v, 0 %.op = add nuw nsw i32 %cnt, 1 %add = select i1 %tobool, i32 0, i32 %.op and x86 asm code: bsfl %edi, %ecx addl $1, %ecx testl %edi, %edi movl $0, %eax cmovnel %ecx, %eax In this case the 'test' instruction can't be eliminated because the 'add' instruction modifies the EFLAGS, namely, ZF flag that is set by the 'bsf' instruction when 'x' is zero. We now produce the following code: bsfl %edi, %ecx movl $-1, %eax cmovnel %ecx, %eax addl $1, %eax Patch by Ivan Kulagin Reviewers: davide, craig.topper, spatel, RKSimon Reviewed By: craig.topper Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D48765 llvm-svn: 336768
The LLVM Compiler Infrastructure ================================ This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you are writing a package for LLVM, see docs/Packaging.rst for our suggestions.