https://bugs.llvm.org/show_bug.cgi?id=32802
Bug ID: 32802
Summary: [BranchFolding] Investigate reducing the default value
of tail-merge-size
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Transformation Utilities
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: andrew.v.tische...@gmail.com, dav...@freebsd.org,
fil...@gmail.com, jlpaq...@uvic.ca,
llvm-bugs@lists.llvm.org, ma...@braunis.de
llvm\lib\CodeGen\BranchFolding.cpp:
// Heuristic for tail merging (and, inversely, tail duplication).
// TODO: This should be replaced with a target query.
static cl::opt<unsigned>
TailMergeSize("tail-merge-size",
cl::desc("Min number of instructions to consider tail merging"),
cl::init(3), cl::Hidden);
Currently the tail-merge-size for duplicate BB tail merging is set to a default
value of 3 instructions, which prevents us from merging all the BBs that we
could otherwise (Bug #27136 and D30572). Additionally there appears to be no
testing of this feature at all.
Is the value purely for compile time reasons or does it have to have a value
that must correctly interact with tail-dup-placement-threshold?
Does the TODO comment suggesting making it target specific make sense?
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