mirror of
https://github.com/RPCS3/llvm.git
synced 2024-12-22 12:08:33 +00:00
Old fork of llvm-mirror, used on older RPCS3 builds
de62192843
e.g.
define i32 @t1(i32 %c, i32 %x) nounwind {
%t1 = icmp eq i32 %c, 0
%t2 = lshr i32 %x, 18
%t3 = select i1 %t1, i32 %t2, i32 %x
ret i32 %t3
}
was turned into
define i32 @t2(i32 %c, i32 %x) nounwind {
%t1 = icmp eq i32 %c, 0
%t2 = select i1 %t1, i32 18, i32 0
%t3 = lshr i32 %x, %t2
ret i32 %t3
}
For most targets, that means materializing two constants and then a select. e.g. On x86-64
movl %esi, %eax
shrl $18, %eax
testl %edi, %edi
cmovne %esi, %eax
ret
=>
xorl %eax, %eax
testl %edi, %edi
movl $18, %ecx
cmovne %eax, %ecx
movl %esi, %eax
shrl %cl, %eax
ret
Also, the optimizer and codegen can reason about shl / and / add, etc. by a constant. This optimization will hinder optimizations using ComputeMaskedBits.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68142 91177308-0d34-0410-b5e6-96231b3b80d8
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Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for the Low Level Virtual Machine, 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 HTML documentation provided in docs/index.html for further assistance with LLVM.