https://llvm.org/bugs/show_bug.cgi?id=23639
Bug ID: 23639
Summary: InstCombine: unsigned overflow subtraction
miscompilation
Product: libraries
Version: 3.6
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 14374
--> https://llvm.org/bugs/attachment.cgi?id=14374&action=edit
reduced.c
Introduced in SVN r234388.
Basically, the X - undef -> undef => X - 0 -> {X, false} is mismatching the
__builtin_subcl with a carry in of 0, resulting in it dropping the arithmetic,
causing a miscomputation. The attached test case demonstrates the issue and
reverting the particular change does get it correct as does 3.6.
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