http://llvm.org/bugs/show_bug.cgi?id=22439
Bug ID: 22439
Summary: MachineCSE adds bogosity to MachineOperand flags
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Core LLVM classes
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Consider test/CodeGen/AArch64/arm64-cse.ll run under the machine verifier:
*** Bad machine code: Virtual register def doesn't dominate all uses. ***
- function: t2
- basic block: BB#0 entry (0x7faeab8489b0)
- instruction: %vreg8<def,dead> = SUBSWri %vreg6, 1, 0, %NZCV<imp-def>;
GPR32:%vreg8 GPR32common:%vreg6
LLVM ERROR: Found 1 machine code errors.
This is complaining about:
BB#0: derived from LLVM BB %entry
Live Ins: %X0 %X1
...
%vreg8<def,dead> = SUBSWri %vreg6, 1, 0, %NZCV<imp-def>; GPR32:%vreg8
GPR32common:%vreg6
Bcc 10, <BB#1>, %NZCV<imp-use>
Successors according to CFG: BB#3(12) BB#1(20)
...
BB#1: derived from LLVM BB %if.end
Predecessors according to CFG: BB#0
STRWui %vreg8, %vreg4, 0; mem:ST4[%offset] GPR32:%vreg8 GPR64common:%vreg4
...
%vreg8 is marked as a dead def, but the store in BB#1 is using it.
That block used to have:
%vreg9<def> = SUBSWri %vreg0, 1, 0, %NZCV<imp-def,dead>;
GPR32:%vreg9 GPR32sp:%vreg0
STRWui %vreg9, %vreg4, 0; mem:ST4[%offset] GPR32:%vreg9
GPR64common:%vreg4
MachineCSE recognized that the SUBSWri can be deleted and the value from BB#0
used instead; however, it neglects to update the "dead" flag on %vreg8 when it
does so, and thus introduces bogusness.
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