http://llvm.org/bugs/show_bug.cgi?id=10114
Summary: EltsFromConsecutiveLoads does not preserve chain
successor dependencies from the original loads.
Product: libraries
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Severity: release blocker
Priority: P
Component: Backend: X86
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
The EltsFromConsecutiveLoads in X86ISelLowering.cpp replaces several load
instructions with a single instruction. But if the replaced loads are before a
a call the new load may be inserted after the call, because the dependencies
are not preserved.
For example:
chain
/ \
/ \
V V
load addr load addr+4
| \ / |
| \ / |
| V V |
| token_factor |
| | |
\ | /
\ V /
\ call /
\ /
\ /
\ /
op1 op2
Will be replaced with:
token_factor
|
|
V
call
chain
|
|
V
vload (not guaranteed to be executed before the call)
/ \
/ \
/ \
op1 op2
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