http://llvm.org/bugs/show_bug.cgi?id=22583
Bug ID: 22583
Summary: [EarlyCSE] Missed trivial dead store case
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Early CSE currently does not handle this case:
; Function Attrs: readonly
declare void @readmem() #0
define void @test(i64* %ptr) {
%v = load i64* %ptr
store i64 %v, i64* %ptr
call void @readmem()
ret void
}
attributes #0 = { readonly }
The store is dead since it's writing back the same value which was read. Given
both are simple (non volatile, non ordered) the store can just be removed.
EarlyCSE has all the information to do this. Load is part of the available
load set. We know we haven't crossed an ordering set (if available load set is
non-empty).
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