https://llvm.org/bugs/show_bug.cgi?id=30501
Bug ID: 30501
Summary: AVX512: LLVM generates invalid instructions on Xeon
Phi (SIGILL: illegal instruction operand), crashes
ensue
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: wenzel.ja...@epfl.ch
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Hi,
LLVM occasionally generates invalid instructions that crash my application
running on Xeon Phi (KNL).
I've been able to reduce one such crash to a minimal example compiled with the
following flags:
$ clang++ -march=knl -stdlib=libc++ -O0 -fno-rtti -fno-exceptions -o test
test.cpp
===========================
#include <immintrin.h>
#define ALWAYS_INLINE __attribute__ ((always_inline)) inline
struct KMask {
__mmask8 k;
ALWAYS_INLINE KMask(bool value) : k(__mmask8(value ? -1 : 0)) { }
};
int main(int /* argc */, char * /*argv */ []) {
KMask m(true);
return 0;
}
===========================
LLDB session illustrating the crash:
(lldb) target create "test"
Current executable set to 'test' (x86_64).
error: Unrecognized command 'rujn'.
(lldb) run
Process 83258 launched: '/home/wjakob/simdarray/test' (x86_64)
Process 83258 stopped
* thread #1: tid = 83258, 0x000000000040069d test`main + 45, name = 'test',
stop reason = signal SIGILL: illegal instruction operand
frame #0: 0x000000000040069d test`main + 45
(lldb) d
test`main:
0x400670 <+0>: push rbp
0x400671 <+1>: mov rbp, rsp
0x400674 <+4>: xor eax, eax
0x400676 <+6>: mov ecx, 0xffffffff
0x40067b <+11>: lea rdx, [rbp - 0x28]
0x40067f <+15>: mov dword ptr [rbp - 0x10], 0x0
0x400686 <+22>: mov dword ptr [rbp - 0x14], edi
0x400689 <+25>: mov qword ptr [rbp - 0x20], rsi
===========================
This is the assembly output I get when compiling with "-S":
.text
.file "test.cpp"
.globl main
.p2align 4, 0x90
.type main,@function
main: # @main
.cfi_startproc
# BB#0:
pushq %rbp
.Ltmp0:
.cfi_def_cfa_offset 16
.Ltmp1:
.cfi_offset %rbp, -16
movq %rsp, %rbp
.Ltmp2:
.cfi_def_cfa_register %rbp
xorl %eax, %eax
movl $4294967295, %ecx # imm = 0xFFFFFFFF
leaq -40(%rbp), %rdx
movl $0, -16(%rbp)
movl %edi, -20(%rbp)
movq %rsi, -32(%rbp)
movq %rdx, -8(%rbp)
movb $1, -9(%rbp)
movq -8(%rbp), %rdx
movb -9(%rbp), %r8b
kortestw %r8b, %r8b
movl %eax, %edi
cmovnel %ecx, %edi
movb %dil, %r8b
movb %r8b, (%rdx)
popq %rbp
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
.cfi_endproc
.ident "clang version 4.0.0 (trunk 282142)"
.section ".note.GNU-stack","",@progbits
===========================
This is the LLVM IR corresponding to the same code
; ModuleID = 'tests/testsuite.cpp'
source_filename = "tests/testsuite.cpp"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
%struct.KMask = type { i8 }
; Function Attrs: norecurse nounwind uwtable
define i32 @main(i32, i8**) #0 {
%3 = alloca %struct.KMask*, align 8
%4 = alloca i8, align 1
%5 = alloca i32, align 4
%6 = alloca i32, align 4
%7 = alloca i8**, align 8
%8 = alloca %struct.KMask, align 1
store i32 0, i32* %5, align 4
store i32 %0, i32* %6, align 4
store i8** %1, i8*** %7, align 8
store %struct.KMask* %8, %struct.KMask** %3, align 8
store i8 1, i8* %4, align 1
%9 = load %struct.KMask*, %struct.KMask** %3, align 8
%10 = getelementptr inbounds %struct.KMask, %struct.KMask* %9, i32 0, i32 0
%11 = load i8, i8* %4, align 1
%12 = trunc i8 %11 to i1
%13 = select i1 %12, i32 -1, i32 0
%14 = trunc i32 %13 to i8
store i8 %14, i8* %10, align 1
ret i32 0
}
attributes #0 = { norecurse nounwind uwtable
"correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false"
"less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
"no-jump-tables"="false" "no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false" "no-trapping-math"="false"
"stack-protector-buffer-size"="8" "target-cpu"="knl"
"target-features"="+adx,+aes,+avx,+avx2,+avx512cd,+avx512er,+avx512f,+avx512pf,+bmi,+bmi2,+cx16,+f16c,+fma,+fsgsbase,+fxsr,+lzcnt,+mmx,+movbe,+pclmul,+popcnt,+prefetchwt1,+rdrnd,+rdseed,+rtm,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave,+xsaveopt"
"unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.ident = !{!0}
!0 = !{!"clang version 4.0.0 (trunk 282142)"}
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