https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89721
Segher Boessenkool <segher at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2019-03-14
Ever confirmed|0 |1
--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
The instruction is removed by LRA, something with inheritance.
We have
(insn 16 13 17 2 (set (reg:DF 4 4)
(unspec_volatile:DF [
(const_int 0 [0])
] UNSPECV_MFFS)) "pr89721.c":14:9 931 {rs6000_mffs}
(nil))
and then some code including a call, and then
(insn 23 20 24 2 (set (reg:DF 4 4)
(unspec_volatile:DF [
(const_int 0 [0])
] UNSPECV_MFFS)) "pr89721.c":17:9 931 {rs6000_mffs}
(nil))
LRA does the following to these: (this is powerpc64-linux, default subtarget):
Choosing alt 0 in insn 16: (0) =d {rs6000_mffs}
Creating newreg=133 from oldreg=4, assigning class FLOAT_REGS to r133
16: r133:DF=unspec/v[0] 8
Inserting insn reload after:
36: %4:DF=r133:DF
Creating newreg=134, assigning class NO_REGS to secondary r134
36: r134:DF=r133:DF
Inserting the sec. move after:
37: %4:DF=r134:DF
Choosing alt 0 in insn 23: (0) =d {rs6000_mffs}
Creating newreg=135 from oldreg=4, assigning class FLOAT_REGS to r135
23: r135:DF=unspec/v[0] 8
Inserting insn reload after:
38: %4:DF=r135:DF
Creating newreg=136, assigning class NO_REGS to secondary r136
38: r136:DF=r135:DF
Inserting the sec. move after:
39: %4:DF=r136:DF
********** Inheritance #1: **********
EBB 2
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
Creating newreg=137 from oldreg=133, assigning class FLOAT_REGS to
invariant inheritance r137
16: r133:DF=unspec/v[0] 8
Add invariant inheritance<-original after:
40: r137:DF=r133:DF
23: r135:DF=unspec/v[0] 8
Changing reload<-inheritance after:
41: r135:DF=r137:DF
deleting insn with uid = 23.
Invariant inheritance reuse change 137 (bb2):
23: NOTE_INSN_DELETED
]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
... and the damage is done.
