http://llvm.org/bugs/show_bug.cgi?id=15822
Bug ID: 15822
Summary: DeadStoreElimination ("-dse") eliminates a store that
isn't dead
Product: tools
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: opt
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
DeadStoreElimination ("-dse") eliminates a store that isn't dead.
In the following test case, which is a reduced version of
SingleSource/UnitTests/byval-alignment.c from the LLVM test suite, @do_copy()
should set @g0 to 1234:
@g0 = global i32 zeroinitializer, align 4
@init_val = global i32 1234, align 4
declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32,
i1)
define void @f0(i8* %y) noinline {
tail call void @llvm.memcpy.p0i8.p0i8.i32(i8* bitcast (i32* @g0 to i8*), i8*
%y, i32 4, i32 1, i1 false)
ret void
}
define void @do_copy() {
%copy = alloca i32, align 4
%copy_cast = bitcast i32* %copy to i8*
%init_val_cast = bitcast i32* @init_val to i8*
call void @llvm.memcpy.p0i8.p0i8.i32(i8* %copy_cast, i8* %init_val_cast, i32
4, i32 1, i1 false)
tail call void @f0(i8* %copy_cast)
ret void
}
However, "-dse" removes the memcpy() from @do_copy so that it will copy
uninitialised data to @g0:
$ opt -basicaa -dse byval-min.ll -S -o -
...
define void @do_copy() {
%copy = alloca i32, align 4
%copy_cast = bitcast i32* %copy to i8*
tail call void @f0(i8* %copy_cast)
ret void
}
This also occurs with "opt -std-link-opts".
This occurs in at least LLVM 3.0, 3.1 and r176253.
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