https://bugs.llvm.org/show_bug.cgi?id=44533
Bug ID: 44533
Summary: StraightLineStrengthReduce can introduce UB when
optimizing 2-dim array gep
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: juneyoung....@sf.snu.ac.kr
CC: llvm-bugs@lists.llvm.org
Created attachment 23013
--> https://bugs.llvm.org/attachment.cgi?id=23013&action=edit
Input
```
$ cat slsr-gep.ll
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64-p:64:64:64-p1:32:32:32"
define void @f([10 x [5 x i32]]* %input, i64 %s, i64 %t) {
%p0 = getelementptr inbounds [10 x [5 x i32]], [10 x [5 x i32]]* %input, i64
0, i64 %s, i64 %t
call void @foo(i32* %p0)
%s2 = shl nsw i64 %s, 1
%p1 = getelementptr inbounds [10 x [5 x i32]], [10 x [5 x i32]]* %input, i64
0, i64 %s2, i64 %t
call void @foo(i32* %p1)
ret void
}
declare void @foo(i32*)
$ opt -slsr -S -o - slsr-gep.ll
; ModuleID = 'slsr-gep.ll'
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64-p:64:64:64-p1:32:32:32"
define void @f([10 x [5 x i32]]* %input, i64 %s, i64 %t) {
%p0 = getelementptr inbounds [10 x [5 x i32]], [10 x [5 x i32]]* %input, i64
0, i64 %s, i64 %t
call void @foo(i32* %p0)
%1 = mul i64 %s, 5
%p1 = getelementptr inbounds i32, i32* %p0, i64 %1
call void @foo(i32* %p1)
ret void
}
declare void @foo(i32*)
```
(the test excerpted from Transforms/StraightLineStrengthReduce/slsr-gep.ll)
This is incorrect when input[s][t] is not inbounds but input[s2][t] is
inbounds.
For example, if s = 1, s2 = 2, and t = -6, it can happen.
After optimization, %p1 becomes poison.
One possible solution for this is to allow the transformation when %s and %t
have a same sign bit. Will this solution be effective enough?
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