mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-10-24 13:33:37 +02:00
ef448d0349
This patch contains a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions into a conditional branch (Bcc), when the NZCV flags can be set for "free". This is preferred on targets that have more flexibility when scheduling Bcc instructions as compared to CBZ/CBNZ/TBZ/TBNZ (assuming all other variables are equal). This can reduce register pressure and is also the default behavior for GCC. A few examples: add w8, w0, w1 -> cmn w0, w1 ; CMN is an alias of ADDS. cbz w8, .LBB_2 -> b.eq .LBB0_2 ; single def/use of w8 removed. add w8, w0, w1 -> adds w8, w0, w1 ; w8 has multiple uses. cbz w8, .LBB1_2 -> b.eq .LBB1_2 sub w8, w0, w1 -> subs w8, w0, w1 ; w8 has multiple uses. tbz w8, #31, .LBB6_2 -> b.ge .LBB6_2 In looking at all current sub-target machine descriptions, this transformation appears to be either positive or neutral. Differential Revision: https://reviews.llvm.org/D34220. llvm-svn: 306144
29 lines
769 B
LLVM
29 lines
769 B
LLVM
; RUN: llc -o - %s -mattr=+arith-cbz-fusion | FileCheck %s
|
|
; RUN: llc -o - %s -mcpu=cyclone | FileCheck %s
|
|
|
|
target triple = "aarch64-unknown"
|
|
|
|
declare void @foobar(i32 %v0, i32 %v1)
|
|
|
|
; Make sure sub is scheduled in front of cbnz
|
|
; CHECK-LABEL: test_sub_cbz:
|
|
; CHECK: subs w[[SUBRES:[0-9]+]], w0, #13
|
|
; CHECK: b.ne {{.?LBB[0-9_]+}}
|
|
define void @test_sub_cbz(i32 %a0, i32 %a1) {
|
|
entry:
|
|
; except for the fusion opportunity the sub/add should be equal so the
|
|
; scheduler would leave them in source order if it weren't for the scheduling
|
|
%v0 = sub i32 %a0, 13
|
|
%cond = icmp eq i32 %v0, 0
|
|
%v1 = add i32 %a1, 7
|
|
br i1 %cond, label %if, label %exit
|
|
|
|
if:
|
|
call void @foobar(i32 %v1, i32 %v0)
|
|
br label %exit
|
|
|
|
exit:
|
|
call void @foobar(i32 %v0, i32 %v1)
|
|
ret void
|
|
}
|