Restrict call metadata based hotness detection to Sample PGO mode

Summary:
Don't use the metadata on call instructions for determining hotness
unless we are in sample PGO mode, where it is needed because profile
counts are not accurate. In instrumentation mode this is not necessary
and does more harm than good when calls have VP metadata that hasn't
been properly scaled after transformations or dropped after constant
prop based devirtualization (both should be fixed, but we don't need
to do this in the first place for instrumentation PGO).

This required adjusting a number of tests to distinguish between sample
and instrumentation PGO handling, and to add in profile summary metadata
so that getProfileCount can get the summary.

Reviewers: davidxl, danielcdh

Subscribers: aemerson, rengolin, mehdi_amini, Prazek, llvm-commits

Differential Revision: https://reviews.llvm.org/D32877

llvm-svn: 302844

1 files changed, 8 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/ProfileSummaryInfo.cpp b/llvm/lib/Analysis/ProfileSummaryInfo.cpp
index 1a53a8ed428..502f4205b68 100644
--- a/llvm/lib/Analysis/ProfileSummaryInfo.cpp
+++ b/llvm/lib/Analysis/ProfileSummaryInfo.cpp
@@ -75,11 +75,14 @@ ProfileSummaryInfo::getProfileCount(const Instruction *Inst,
     return None;
   assert((isa<CallInst>(Inst) || isa<InvokeInst>(Inst)) &&
          "We can only get profile count for call/invoke instruction.");
-  // Check if there is a profile metadata on the instruction. If it is present,
-  // determine hotness solely based on that.
-  uint64_t TotalCount;
-  if (Inst->extractProfTotalWeight(TotalCount))
-    return TotalCount;
+  if (computeSummary() && Summary->getKind() == ProfileSummary::PSK_Sample) {
+    // In sample PGO mode, check if there is a profile metadata on the
+    // instruction. If it is present, determine hotness solely based on that,
+    // since the sampled entry count may not be accurate.
+    uint64_t TotalCount;
+    if (Inst->extractProfTotalWeight(TotalCount))
+      return TotalCount;
+  }
   if (BFI)
     return BFI->getBlockProfileCount(Inst->getParent());
   return None;