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GVN-hoist: limit the length of dependent instructions 

Limit the number of times the while(1) loop is executed. With this restriction
the number of hoisted instructions does not change in a significant way on the
test-suite.

Differential Revision: https://reviews.llvm.org/D23028

llvm-svn: 277651
This commit is contained in:
Sebastian Pop 2016-08-03 20:54:38 +00:00
parent 4ba7c88cc7
commit 2aadad7243
1 changed files with 10 additions and 0 deletions
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10
llvm/lib/Transforms/Scalar/GVNHoist.cpp
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@ -53,6 +53,11 @@ static cl::opt<int> MaxDepthInBB(
cl::desc("Hoist instructions from the beginning of the BB up to the " cl::desc("Hoist instructions from the beginning of the BB up to the "
"maximum specified depth (default = 100, unlimited = -1)")); "maximum specified depth (default = 100, unlimited = -1)"));
static cl::opt<int> MaxChainLength(
"gvn-hoist-max-chain-length", cl::Hidden, cl::init(10),
cl::desc("Maximum length of dependent chains to hoist "
"(default = 10, unlimited = -1)"));
namespace { namespace {
// Provides a sorting function based on the execution order of two instructions. // Provides a sorting function based on the execution order of two instructions.
@ -212,8 +217,13 @@ public:
DFSNumber[&Inst] = ++I; DFSNumber[&Inst] = ++I;
} }
int ChainLength = 0;
// FIXME: use lazy evaluation of VN to avoid the fix-point computation. // FIXME: use lazy evaluation of VN to avoid the fix-point computation.
while (1) { while (1) {
if (MaxChainLength != -1 && ++ChainLength >= MaxChainLength)
return Res;
auto HoistStat = hoistExpressions(F); auto HoistStat = hoistExpressions(F);
if (HoistStat.first + HoistStat.second == 0) if (HoistStat.first + HoistStat.second == 0)
return Res; return Res;