Description
| Bugzilla Link | 35233 |
| Version | 4.0 |
| OS | Linux |
| Attachments | C++11 file exhibiting the bug |
| Reporter | LLVM Bugzilla Contributor |
| CC | @andykaylor,@hfinkel,@rotateright |
Extended Description
A static_cast of a uint64_t to a double on Clang 4.0 and AArch64 is reordered with a fettestexcept, resulting in the wrong floating point state being tested.
Example output from GCC 6.0: https://godbolt.org/g/pbAW4J
Here's Clang's output:
oot@mcsema-aarch64:/remill# ../remill-build/libraries/llvm/bin/clang++ -std=c++11 -O3 -c /tmp/convert.cc -S -o /tmp/convert.S/remill# cat /tmp/convert.S
root@mcsema-aarch64:
.text
.file "/tmp/convert.cc"
.globl _Z9to_doubleR5flagsm
.p2align 2
.type _Z9to_doubleR5flagsm,@function
_Z9to_doubleR5flagsm: // @_Z9to_doubleR5flagsm
// BB#0:
stp x20, x19, [sp, #-32]! // 8-byte Folded Spill
mov x19, x0
orr w0, wzr, #0x1f
stp x29, x30, [sp, #16] // 8-byte Folded Spill
add x29, sp, #16 // =16
mov x20, x1
bl feclearexcept
orr w0, wzr, #0x1f
bl fetestexcept
tbz w0, #4, .LBB0_2
// BB#1:
orr w8, wzr, #0x1
str w8, [x19]
.LBB0_2:
tbz w0, #2, .LBB0_4
// BB#3:
orr w8, wzr, #0x1
str w8, [x19, #4]
.LBB0_4:
tbz w0, #3, .LBB0_6
// BB#5:
orr w8, wzr, #0x1
str w8, [x19, #8]
.LBB0_6:
ucvtf d0, x20
tbz w0, #0, .LBB0_8
// BB#7:
orr w8, wzr, #0x1
str w8, [x19, #12]
.LBB0_8:
ldp x29, x30, [sp, #16] // 8-byte Folded Reload
ldp x20, x19, [sp], #32 // 8-byte Folded Reload
ret
.Lfunc_end0:
.size _Z9to_doubleR5flagsm, .Lfunc_end0-_Z9to_doubleR5flagsm