http://llvm.org/bugs/show_bug.cgi?id=20647
Bug ID: 20647
Summary: Worse codegen than gcc for heaps of bit arith
Product: libraries
Version: 3.4
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Look here for a comparison and related source code side-by-side.
https://gist.github.com/kvanberendonck/3d072ae0f450f20cf1ed
What I've noticed mainly is that while gcc performs the arith directly on the
memory location, llvm produces many more instructions because it chooses to
load it into a register first, perform the arith and then write it back. It
also generates twice as many ORs... not sure why.
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