Add functions for finding ephemeral values

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).

llvm-svn: 217335

1 files changed, 10 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
index d3140f9a76d..ef434837720 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -104,7 +104,8 @@ namespace {
 
       // Analyze loop. Check its size, calculate is it possible to unswitch
       // it. Returns true if we can unswitch this loop.
-      bool countLoop(const Loop *L, const TargetTransformInfo &TTI);
+      bool countLoop(const Loop *L, const TargetTransformInfo &TTI,
+                     AssumptionTracker *AT);
 
       // Clean all data related to given loop.
       void forgetLoop(const Loop *L);
@@ -215,7 +216,8 @@ namespace {
 
 // Analyze loop. Check its size, calculate is it possible to unswitch
 // it. Returns true if we can unswitch this loop.
-bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI) {
+bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI,
+                                AssumptionTracker *AT) {
 
   LoopPropsMapIt PropsIt;
   bool Inserted;
@@ -232,13 +234,16 @@ bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI) {
     // large numbers of branches which cause loop unswitching to go crazy.
     // This is a very ad-hoc heuristic.
 
+    SmallPtrSet<const Value *, 32> EphValues;
+    CodeMetrics::collectEphemeralValues(L, AT, EphValues);
+
     // FIXME: This is overly conservative because it does not take into
     // consideration code simplification opportunities and code that can
     // be shared by the resultant unswitched loops.
     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);
 
     Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
     Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
@@ -426,7 +431,8 @@ bool LoopUnswitch::processCurrentLoop() {
 
   // Probably we reach the quota of branches for this loop. If so
   // stop unswitching.
-  if (!BranchesInfo.countLoop(currentLoop, getAnalysis<TargetTransformInfo>()))
+  if (!BranchesInfo.countLoop(currentLoop, getAnalysis<TargetTransformInfo>(),
+                              AT))
     return false;
 
   // Loop over all of the basic blocks in the loop.  If we find an interior