https://llvm.org/bugs/show_bug.cgi?id=31363
Bug ID: 31363
Summary: Lowering operations to compiler intrinsics with
reference parameters generates bad code
Product: libraries
Version: 3.9
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Common Code Generator Code
Assignee: unassignedb...@nondot.org
Reporter: simonas+llvm....@kazlauskas.me
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Consider this snippet of LLVM IR:
```llvm
target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-windows-msvc"
; Function Attrs: nounwind uwtable
define void @test3(i128* noalias nocapture sret dereferenceable(16), i128*
noalias readonly nocapture dereferenceable(16), i128* noalias readonly
nocapture dereferenceable(16)) unnamed_addr #0 {
start:
%3 = load i128, i128* %1
%4 = load i128, i128* %2
%5 = udiv i128 %3, %4
store i128 %5, i128* %0
ret void
}
attributes #0 = { nounwind uwtable }
```
This generates following assembly:
```asm
test3:
push rsi
.seh_pushreg 6
sub rsp, 64
.seh_stackalloc 64
.seh_endprologue
mov rsi, rcx
mov r9, qword ptr [rdx]
mov rcx, qword ptr [rdx + 8]
mov rdx, qword ptr [r8]
mov rax, qword ptr [r8 + 8]
mov qword ptr [rsp + 56], rcx
mov qword ptr [rsp + 48], r9
mov qword ptr [rsp + 40], rax
mov qword ptr [rsp + 32], rdx
lea rcx, [rsp + 48]
lea rdx, [rsp + 32]
call __udivti3
pshufd xmm1, xmm0, 78 # xmm1 = xmm0[2,3,0,1]
movq qword ptr [rsi], xmm0
movq qword ptr [rsi + 8], xmm1
mov rax, rsi
add rsp, 64
pop rsi
ret
.seh_handlerdata
.text
.seh_endproc
```
noting that LLVM thinks __udivti3 looks like this when targetting windows:
```
declare i128 @__udivti3(i128* readonly nocapture dereferenceable(16), i128*
readonly nocapture dereferenceable(16));
```
its easy to see that there’s way too much stack trashing going on and the
assembly instead could be just this:
```
test3:
push rsi
.seh_pushreg 6
sub rsp, 32
.seh_stackalloc 32
.seh_endprologue
mov rsi, rcx
mov rcx, rdx
mov rdx, r8
call __udivti3
pshufd xmm1, xmm0, 78 # xmm1 = xmm0[2,3,0,1]
movq qword ptr [rsi], xmm0
movq qword ptr [rsi + 8], xmm1
mov rax, rsi
add rsp, 32
pop rsi
ret
.seh_handlerdata
.text
.seh_endproc
```
which only does write to the sret parameter, as one would expect from a well
optimised code.
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
