diff options
| -rw-r--r-- | llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp | 17 | ||||
| -rw-r--r-- | llvm/test/Transforms/LoopUnroll/partial-unroll-optsize.ll | 19 | ||||
| -rw-r--r-- | llvm/test/Transforms/LoopUnroll/runtime-loop2.ll | 2 |
3 files changed, 31 insertions, 7 deletions
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp index 4467112a181..fef52107f62 100644 --- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp +++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -222,8 +222,11 @@ static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, // Don't allow an estimate of size zero. This would allows unrolling of loops // with huge iteration counts, which is a compile time problem even if it's - // not a problem for code quality. - if (LoopSize == 0) LoopSize = 1; + // not a problem for code quality. Also, the code using this size may assume + // that each loop has at least three instructions (likely a conditional + // branch, a comparison feeding that branch, and some kind of loop increment + // feeding that comparison instruction). + LoopSize = std::max(LoopSize, 3u); return LoopSize; } @@ -407,7 +410,11 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, &AC); DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); - uint64_t UnrolledSize = (uint64_t)LoopSize * Count; + + // When computing the unrolled size, note that the conditional branch on the + // backedge and the comparison feeding it are not replicated like the rest of + // the loop body (which is why 2 is subtracted). + uint64_t UnrolledSize = (uint64_t)(LoopSize-2) * Count + 2; if (notDuplicatable) { DEBUG(dbgs() << " Not unrolling loop which contains non-duplicatable" << " instructions.\n"); @@ -452,7 +459,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { } if (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) { // Reduce unroll count to be modulo of TripCount for partial unrolling. - Count = PartialThreshold / LoopSize; + Count = (std::max(PartialThreshold, 3u)-2) / (LoopSize-2); while (Count != 0 && TripCount % Count != 0) Count--; } @@ -466,7 +473,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { // the original count which satisfies the threshold limit. while (Count != 0 && UnrolledSize > PartialThreshold) { Count >>= 1; - UnrolledSize = LoopSize * Count; + UnrolledSize = (LoopSize-2) * Count + 2; } if (Count > UP.MaxCount) Count = UP.MaxCount; diff --git a/llvm/test/Transforms/LoopUnroll/partial-unroll-optsize.ll b/llvm/test/Transforms/LoopUnroll/partial-unroll-optsize.ll index 3179d55e978..a650317f3df 100644 --- a/llvm/test/Transforms/LoopUnroll/partial-unroll-optsize.ll +++ b/llvm/test/Transforms/LoopUnroll/partial-unroll-optsize.ll @@ -1,7 +1,7 @@ ; RUN: opt < %s -S -loop-unroll -unroll-allow-partial | FileCheck %s ; Loop size = 3, when the function has the optsize attribute, the ; OptSizeUnrollThreshold, i.e. 50, is used, hence the loop should be unrolled -; by 16 times because 3 * 16 < 50. +; by 32 times because (1 * 32) + 2 < 50 (whereas (1 * 64 + 2) is not). define void @unroll_opt_for_size() nounwind optsize { entry: br label %loop @@ -32,4 +32,21 @@ exit: ; CHECK-NEXT: add ; CHECK-NEXT: add ; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add +; CHECK-NEXT: add ; CHECK-NEXT: icmp + diff --git a/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll b/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll index 7205c686065..176362a3445 100644 --- a/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll +++ b/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll @@ -1,4 +1,4 @@ -; RUN: opt < %s -S -loop-unroll -unroll-threshold=50 -unroll-runtime -unroll-count=8 | FileCheck %s +; RUN: opt < %s -S -loop-unroll -unroll-threshold=25 -unroll-runtime -unroll-count=8 | FileCheck %s ; Choose a smaller, power-of-two, unroll count if the loop is too large. ; This test makes sure we're not unrolling 'odd' counts |
