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LLVM ERROR: Use not jointly dominated by defs. after simple-register-coalescing #37871

Open Quuxplusone opened 6 years ago

Quuxplusone commented 6 years ago
Bugzilla Link PR38898
Status NEW
Importance P enhancement
Reported by Mikael Holmén (mikael.holmen@ericsson.com)
Reported on 2018-09-10 23:12:26 -0700
Last modified on 2018-11-09 02:57:07 -0800
Version trunk
Hardware PC Linux
CC llvm-bugs@lists.llvm.org, quentin.colombet@gmail.com
Fixed by commit(s)
Attachments coalesce.mir (502 bytes, text/plain)
Blocks
Blocked by
See also 
Created attachment 20864
reproducer

Reproduce with
 llc -o - coalesce.mir -march=amdgcn -run-pass simple-register-coalescing -verify-machineinstrs

which gives

Use of $noreg does not have a corresponding definition on every path:
48r %2.sub0:sreg_64 = IMPLICIT_DEF
LLVM ERROR: Use not jointly dominated by defs.

-debug shows

...
0B      bb.0:
          successors: %bb.1(0x80000000); %bb.1(100.00%)

16B       %0:sreg_32 = IMPLICIT_DEF
32B       %1:sreg_32 = IMPLICIT_DEF
48B       undef %2.sub0:sreg_64 = IMPLICIT_DEF
64B       %2.sub1:sreg_64 = COPY %1:sreg_32
...

...
64B     %2.sub1:sreg_64 = COPY %1:sreg_32
        Considering merging to SReg_64 with %1 in %2:sub1
                RHS = %1 [32r,64r:0)  0@32r weight:0.000000e+00
                LHS = %2 [16r,48r:1)[48r,64r:2)[64r,80B:4)[80B,112B:6)[128r,144r:0)[144r,176B:3)[176B,240r:5)  0@128r 1@16r 2@48r 3@144r 4@64r 5@176B-phi 6@80B-phi L00000001 [48r,80B:1)[80B,112B:3)[128r,176B:0)[176B,224r:2)  0@128r 1@48r 2@176B-phi 3@80B-phi L00000002 [64r,80B:2)[80B,112B:4)[144r,176B:0)[176B,240r:3)  0@144r 1@x 2@64r 3@176B-phi 4@80B-phi weight:0.000000e+00
...
                erased: 16r     undef %2.sub1:sreg_64 = IMPLICIT_DEF
                erased: 64r     %2.sub1:sreg_64 = COPY %1:sreg_32
                erased: 32r     %1:sreg_32 = IMPLICIT_DEF
...

So we end up with this bb.0:

0B  bb.0:
     successors: %bb.1(0x80000000); %bb.1(100.00%)

48B  %2.sub0:sreg_64 = IMPLICIT_DEF

Originally found when compiling for an out-of-tree target.

Thanks to Matthias Braun for the above AMDGPU reproducer.
Quuxplusone commented 6 years ago

Attached coalesce.mir (502 bytes, text/plain): reproducer