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author | Eli Bendersky <eliben@google.com> | 2014-06-11 23:15:35 +0000 |
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committer | Eli Bendersky <eliben@google.com> | 2014-06-11 23:15:35 +0000 |
commit | 87fcb536ab8e70f3578c88c57d12c2ffee86abd2 (patch) | |
tree | 2f009c8acf0c8bb04b5f2b101fca29d6d389a74e /lib | |
parent | 02503401b4668c068e6bf032935eac4a97fd7b8d (diff) | |
download | llvm-87fcb536ab8e70f3578c88c57d12c2ffee86abd2.tar.gz llvm-87fcb536ab8e70f3578c88c57d12c2ffee86abd2.tar.bz2 llvm-87fcb536ab8e70f3578c88c57d12c2ffee86abd2.tar.xz |
Teach LoopUnrollPass to respect loop unrolling hints in metadata.
See http://reviews.llvm.org/D4090 for more details.
The Clang change that produces this metadata was committed in r210667
Patch by Mark Heffernan.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210721 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r-- | lib/Transforms/Scalar/LoopUnrollPass.cpp | 115 |
1 files changed, 109 insertions, 6 deletions
diff --git a/lib/Transforms/Scalar/LoopUnrollPass.cpp b/lib/Transforms/Scalar/LoopUnrollPass.cpp index fc28fd2bdc..e32869226d 100644 --- a/lib/Transforms/Scalar/LoopUnrollPass.cpp +++ b/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -20,6 +20,7 @@ #include "llvm/IR/DataLayout.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Metadata.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" @@ -36,7 +37,8 @@ UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden, static cl::opt<unsigned> UnrollCount("unroll-count", cl::init(0), cl::Hidden, - cl::desc("Use this unroll count for all loops, for testing purposes")); + cl::desc("Use this unroll count for all loops including those with " + "unroll_count pragma values, for testing purposes")); static cl::opt<bool> UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden, @@ -47,6 +49,13 @@ static cl::opt<bool> UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden, cl::desc("Unroll loops with run-time trip counts")); +// Maximum allowed unroll count for a loop being fully unrolled +// because of a pragma unroll(enable) statement (ie, metadata +// "llvm.loopunroll.enable" is true). This prevents unexpected +// behavior like crashing when using this pragma on high trip count +// loops. +static const unsigned PragmaFullUnrollCountLimit = 1024; + namespace { class LoopUnroll : public LoopPass { public: @@ -151,6 +160,63 @@ static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, return LoopSize; } +// Returns the value associated with the given metadata node name (for +// example, "llvm.loopunroll.count"). If no such named metadata node +// exists, then nullptr is returned. +static const ConstantInt *GetUnrollMetadataValue(const Loop *L, + StringRef Name) { + MDNode *LoopID = L->getLoopID(); + if (!LoopID) return nullptr; + + // First operand should refer to the loop id itself. + assert(LoopID->getNumOperands() > 0 && "requires at least one operand"); + assert(LoopID->getOperand(0) == LoopID && "invalid loop id"); + + for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) { + const MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i)); + if (!MD) continue; + + const MDString *S = dyn_cast<MDString>(MD->getOperand(0)); + if (!S) continue; + + if (Name.equals(S->getString())) { + assert(MD->getNumOperands() == 2 && + "Unroll hint metadata should have two operands."); + return cast<ConstantInt>(MD->getOperand(1)); + } + } + return nullptr; +} + +// Returns true if the loop has an unroll(enable) pragma. +static bool HasUnrollEnablePragma(const Loop *L) { + const ConstantInt *EnableValue = + GetUnrollMetadataValue(L, "llvm.loopunroll.enable"); + return (EnableValue && EnableValue->getZExtValue()); + return false; +} + +// Returns true if the loop has an unroll(disable) pragma. +static bool HasUnrollDisablePragma(const Loop *L) { + const ConstantInt *EnableValue = + GetUnrollMetadataValue(L, "llvm.loopunroll.enable"); + return (EnableValue && !EnableValue->getZExtValue()); + return false; +} + +// Check for unroll_count(N) pragma. If found, return true and set +// Count to the integer parameter of the pragma. +static bool HasUnrollCountPragma(const Loop *L, int &Count) { + const ConstantInt *CountValue = + GetUnrollMetadataValue(L, "llvm.loopunroll.count"); + if (CountValue) { + Count = CountValue->getZExtValue(); + assert(Count >= 1 && "Unroll count must be positive."); + return true; + } + return false; +} + bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { if (skipOptnoneFunction(L)) return false; @@ -202,12 +268,49 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock); } - bool Runtime = UserRuntime ? CurrentRuntime : UP.Runtime; + // User-specified count (either as a command-line option or + // constructor parameter) has highest precedence. + unsigned Count = UserCount ? CurrentCount : 0; - // Use a default unroll-count if the user doesn't specify a value - // and the trip count is a run-time value. The default is different - // for run-time or compile-time trip count loops. - unsigned Count = UserCount ? CurrentCount : UP.Count; + // If there is no user-specified count, unroll pragmas have the next + // highest precendence. + if (Count == 0) { + if (HasUnrollDisablePragma(L)) { + // Loop has unroll(disable) pragma. + return false; + } + + int PragmaCount; + if (HasUnrollCountPragma(L, PragmaCount)) { + if (PragmaCount == 1) { + // Nothing to do. + return false; + } + Count = PragmaCount; + Threshold = NoThreshold; + } else if (HasUnrollEnablePragma(L)) { + // Loop has unroll(enable) pragma without a unroll_count pragma, + // so unroll loop fully if possible. + if (TripCount == 0) { + DEBUG(dbgs() << " Loop has unroll(enable) pragma but loop cannot be " + "fully unrolled because trip count is unknown.\n"); + // Continue with standard heuristic unrolling. + } else if (TripCount > PragmaFullUnrollCountLimit) { + DEBUG(dbgs() << " Loop has unroll(enable) pragma but loop cannot be " + "fully unrolled because loop count is greater than " + << PragmaFullUnrollCountLimit); + // Continue with standard heuristic unrolling. + } else { + Count = TripCount; + Threshold = NoThreshold; + } + } + } + + if (Count == 0) + Count = UP.Count; + + bool Runtime = UserRuntime ? CurrentRuntime : UP.Runtime; if (Runtime && Count == 0 && TripCount == 0) Count = UnrollRuntimeCount; |