[CSSPGO] Deduplicating dangling pseudo probes.

Same dangling probes are redundant since they all have the same semantic that is to rely on the counts inference tool to get reasonable count for the same original block. Therefore, there's no need to keep multiple copies of them. I've seen jump threading created tons of redundant dangling probes that slowed down the compiler dramatically. Other optimization passes can also result in redundant probes though without an observed impact so far.

This change removes block-wise redundant dangling probes specifically introduced by jump threading. To support removing redundant dangling probes caused by all other passes, a final function-wise deduplication is also added.

An 18% size win of the .pseudo_probe section was seen for SPEC2017. No performance difference was observed.

Differential Revision: https://reviews.llvm.org/D97482

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 31948dd..9697e7d 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -33,6 +33,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/PseudoProbe.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/User.h"
 #include "llvm/IR/Value.h"
@@ -432,7 +433,7 @@ static bool removeRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
   return !ToBeRemoved.empty();
 }
 
-bool llvm::RemoveRedundantDbgInstrs(BasicBlock *BB) {
+bool llvm::RemoveRedundantDbgInstrs(BasicBlock *BB, bool RemovePseudoOp) {
   bool MadeChanges = false;
   // By using the "backward scan" strategy before the "forward scan" strategy we
   // can remove both dbg.value (2) and (3) in a situation like this:
@@ -447,6 +448,8 @@ bool llvm::RemoveRedundantDbgInstrs(BasicBlock *BB) {
   // already is described as having the value V1 at (1).
   MadeChanges |= removeRedundantDbgInstrsUsingBackwardScan(BB);
   MadeChanges |= removeRedundantDbgInstrsUsingForwardScan(BB);
+  if (RemovePseudoOp)
+    MadeChanges |= removeRedundantPseudoProbes(BB);
 
   if (MadeChanges)
     LLVM_DEBUG(dbgs() << "Removed redundant dbg instrs from: "