http://llvm.org/bugs/show_bug.cgi?id=22578
Bug ID: 22578
Summary: [Reassociate] Use localized Changed flag to avoid
calls to RewriteExprTree
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
The Reassociation pass uses a global flag to determine if something in the IR
has changed. The flag should be maintained per expression to avoid calls to
RewriteExprTree.
If the expression hasn't changed in some non-trivial way, then the rewriting is
unnecessary. Rewriting an unchanged expressions increases compile-time, drops
unsigned/signed wrap flags and generally results in a completely different
expression topology. I'm seeing that the rewriting generally produces the
longest critical path, which is especially bad for FP code.
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