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When code size is the priority (Oz, MinSize attribute), help llvm

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turning a code like this:

if (foo)
   free(foo)

into that:
free(foo)

Move a call to free from basic block FB into FB's predecessor, P,
when the path from P to FB is taken only if the argument of free is
not equal to NULL.

Some restrictions apply on P and FB to be sure that this code motion
is profitable. Namely:
1. FB must have only one predecessor P.
2. FB must contain only the call to free plus an unconditional
   branch to S.
3. P's successors are FB and S.

Because of 1., we will not increase the code size when moving the call
to free from FB to P.
Because of 2., FB will be empty after the move.
Because of 2. and 3., P's branch instruction becomes useless, so as FB
(simplifycfg will do the job).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171762 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Quentin Colombet
2013-01-07 18:37:41 +00:00
parent 50601e4af1
commit 637582eaf7
4 changed files with 119 additions and 0 deletions
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19
include/llvm/Support/PatternMatch.h
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@ -781,6 +781,25 @@ inline fneg_match<LHS> m_FNeg(const LHS &L) { return L; }
// Matchers for control flow.
//
struct br_match {
BasicBlock *&Succ;
br_match(BasicBlock *&Succ)
: Succ(Succ) {
}
template<typename OpTy>
bool match(OpTy *V) {
if (BranchInst *BI = dyn_cast<BranchInst>(V))
if (BI->isUnconditional()) {
Succ = BI->getSuccessor(0);
return true;
}
return false;
}
};
inline br_match m_UnconditionalBr(BasicBlock *&Succ) { return br_match(Succ); }
template<typename Cond_t>
struct brc_match {
Cond_t Cond;