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Add functions for finding ephemeral values

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This adds a set of utility functions for collecting 'ephemeral' values. These
are LLVM IR values that are used only by @llvm.assume intrinsics (directly or
indirectly), and thus will be removed prior to code generation, implying that
they should be considered free for certain purposes (like inlining). The
inliner's cost analysis, and a few other passes, have been updated to account
for ephemeral values using the provided functionality.

This functionality is important for the usability of @llvm.assume, because it
limits the "non-local" side-effects of adding llvm.assume on inlining, loop
unrolling, etc. (these are hints, and do not generate code, so they should not
directly contribute to estimates of execution cost).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217335 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-09-07 13:49:57 +00:00
parent 3666e7f4c1
commit 3d03d60ca8
9 changed files with 222 additions and 17 deletions
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10
lib/Transforms/Scalar/LoopUnrollPass.cpp
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@@ -203,11 +203,15 @@ Pass *llvm::createSimpleLoopUnrollPass() {
/// ApproximateLoopSize - Approximate the size of the loop.
static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
bool &NotDuplicatable,
const TargetTransformInfo &TTI) {
const TargetTransformInfo &TTI,
AssumptionTracker *AT) {
SmallPtrSet<const Value *, 32> EphValues;
CodeMetrics::collectEphemeralValues(L, AT, EphValues);
CodeMetrics Metrics;
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I)
Metrics.analyzeBasicBlock(*I, TTI);
Metrics.analyzeBasicBlock(*I, TTI, EphValues);
NumCalls = Metrics.NumInlineCandidates;
NotDuplicatable = Metrics.notDuplicatable;
@@ -391,7 +395,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
unsigned NumInlineCandidates;
bool notDuplicatable;
unsigned LoopSize =
ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI);
ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, AT);
DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n");
uint64_t UnrolledSize = (uint64_t)LoopSize * Count;
if (notDuplicatable) {