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, 9 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 71f01f4..1667204 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -13,6 +13,7 @@
 
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AssumptionTracker.h"
 #include "llvm/Analysis/CodeMetrics.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/LoopPass.h"
@@ -53,6 +54,7 @@ namespace {
 
     // LCSSA form makes instruction renaming easier.
     void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addRequired<AssumptionTracker>();
       AU.addPreserved<DominatorTreeWrapperPass>();
       AU.addRequired<LoopInfo>();
       AU.addPreserved<LoopInfo>();
@@ -72,12 +74,14 @@ namespace {
     unsigned MaxHeaderSize;
     LoopInfo *LI;
     const TargetTransformInfo *TTI;
+    AssumptionTracker *AT;
   };
 }
 
 char LoopRotate::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
 INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
+INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
 INITIALIZE_PASS_DEPENDENCY(LCSSA)
@@ -98,6 +102,7 @@ bool LoopRotate::runOnLoop(Loop *L, LPPassManager &LPM) {
 
   LI = &getAnalysis<LoopInfo>();
   TTI = &getAnalysis<TargetTransformInfo>();
+  AT = &getAnalysis<AssumptionTracker>();
 
   // Simplify the loop latch before attempting to rotate the header
   // upward. Rotation may not be needed if the loop tail can be folded into the
@@ -323,8 +328,11 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
   // Check size of original header and reject loop if it is very big or we can't
   // duplicate blocks inside it.
   {
+    SmallPtrSet<const Value *, 32> EphValues;
+    CodeMetrics::collectEphemeralValues(L, AT, EphValues);
+
     CodeMetrics Metrics;
-    Metrics.analyzeBasicBlock(OrigHeader, *TTI);
+    Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
     if (Metrics.notDuplicatable) {
       DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
             << " instructions: "; L->dump());