https://bugs.llvm.org/show_bug.cgi?id=36211
Bug ID: 36211
Summary: [DSE] merge memset into earlier store constant
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: spatel+l...@rotateright.com
CC: llvm-bugs@lists.llvm.org
If I've understood correctly, this is an example of the optimization request
made in bug 36129:
declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1)
define void @merge_memset_into_earlier_constant_store(i8* %p) {
%p8 = bitcast i8* %p to i64*
store i64 0, i64* %p8, align 1
%p5 = getelementptr i8, i8* %p, i64 5
tail call void @llvm.memset.p0i8.i64(i8* align 1 %p5, i8 42, i64 3, i1 false)
ret void
}
----------------------------------------------------------------------------
DSE knows how to merge constant stores when they are actual store instructions,
but it doesn't know how to handle this case where we overwrite the last 3 bytes
of p[8] using a memset().
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