https://llvm.org/bugs/show_bug.cgi?id=31142
Bug ID: 31142
Summary: SROA is dropping !nonnull/!range metadata
Product: libraries
Version: 3.9
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: arie...@mail.tau.ac.il
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
When SROA optimizes out an alloca whose load contains a !nonnull metadata, the
load is dropped on the floor.
This can lead to the metadata being dropped in cases such as
define float* @yummy_nonnull(float**) {
entry-block:
%buf = alloca float*
%_0_i8 = bitcast float** %0 to i8*
%_buf_i8 = bitcast float** %buf to i8*
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %_buf_i8, i8* %_0_i8, i64 8, i32
8, i1 false)
%ret = load float*, float** %buf, align 8, !nonnull !0
ret float* %ret
}
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8*
nocapture readonly, i64, i32, i1)
!0 = !{}
Which is optimized to
define float* @yummy_nonnull(float** nocapture readonly) local_unnamed_addr
#0 {
entry-block:
%buf.0.copyload = load float*, float** %0, align 8
ret float* %buf.0.copyload
}
If this function is later inlined, the !nonnull metadata will no longer be
present to help further optimizations.
This is the cause of Rust bug https://github.com/rust-lang/rust/issues/37945.
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