[DSE] Add debug counter.

[fhahn]

Summary

Can be used like -debug-counter=dse-memoryssa-skip=10,dse-memoryssa-counter-count=20

[merge_guards_bot]

Unit tests: unknown.

clang-tidy: unknown.

clang-format: unknown.

Build artifacts: diff.json, console-log.txt

[fhahn]

Needs rebase after bottom-up walk changes/

[fhahn]

Rebase after first patch landed, added test case.

[asbirlea]

lgtm

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

 #include "llvm/IR/Module.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/Value.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/DebugCounter.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <iterator>
 #include <map>
 #include <utility>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "dse"
 
 STATISTIC(NumRedundantStores, "Number of redundant stores deleted");
 STATISTIC(NumFastStores, "Number of stores deleted");
 STATISTIC(NumFastOther, "Number of other instrs removed");
 STATISTIC(NumCompletePartials, "Number of stores dead by later partials");
 STATISTIC(NumModifiedStores, "Number of stores modified");
 
+DEBUG_COUNTER(MemorySSACounter, "dse-memoryssa",
+              "Controls which MemoryDefs are eliminated.");
+
 static cl::opt<bool>
 EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking",
   cl::init(true), cl::Hidden,
   cl::desc("Enable partial-overwrite tracking in DSE"));
 
 static cl::opt<bool>
 EnablePartialStoreMerging("enable-dse-partial-store-merging",
   cl::init(true), cl::Hidden,
while (Optional<MemoryAccess *> Next = State.getDomMemoryDef(
 
       // Before we try to remove anything, check for any extra throwing
       // instructions that block us from DSEing
       if (State.mayThrowBetween(SI, NI, SILocUnd)) {
         LLVM_DEBUG(dbgs() << " stop, may throw!\n");
         break;
       }
 
+      if (!DebugCounter::shouldExecute(MemorySSACounter))
+        break;
+
       // Check if NI overwrites SI.
       int64_t InstWriteOffset, DepWriteOffset;
       InstOverlapIntervalsTy IOL;
       OverwriteResult OR = isOverwrite(SILoc, NILoc, DL, TLI, DepWriteOffset,
                                        InstWriteOffset, NI, IOL, AA, &F);
 
       if (OR == OW_Complete) {
         LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n  DEAD: " << *NI

llvm/test/Transforms/DeadStoreElimination/MSSA/debug-counter.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+
+; Eliminates store to %R in the entry block.
+; RUN: opt < %s -basicaa -dse -enable-dse-memoryssa -debug-counter=dse-memoryssa-skip=0,dse-memoryssa-count=1 -S | FileCheck --check-prefix=SKIP0-COUNT1 %s
+
+; Eliminates store to %P in the entry block.
+; RUN: opt < %s -basicaa -dse -enable-dse-memoryssa -debug-counter=dse-memoryssa-skip=1,dse-memoryssa-count=1 -S | FileCheck --check-prefix=SKIP1-COUNT1 %s
+
+; Eliminates both stores in the entry block.
+; RUN: opt < %s -basicaa -dse -enable-dse-memoryssa -debug-counter=dse-memoryssa-skip=0,dse-memoryssa-count=2 -S | FileCheck --check-prefix=SKIP0-COUNT2 %s
+
+; Eliminates no stores.
+; RUN: opt < %s -basicaa -dse -enable-dse-memoryssa -debug-counter=dse-memoryssa-skip=2,dse-memoryssa-count=1 -S | FileCheck --check-prefix=SKIP2-COUNT1 %s
+
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+
+
+define void @test(i32* noalias %P, i32* noalias %Q, i32* noalias %R) {
+; SKIP0-COUNT1-LABEL: @test(
+; SKIP0-COUNT1-NEXT:    store i32 1, i32* [[P:%.*]]
+; SKIP0-COUNT1-NEXT:    br i1 true, label [[BB1:%.*]], label [[BB2:%.*]]
+; SKIP0-COUNT1:       bb1:
+; SKIP0-COUNT1-NEXT:    br label [[BB3:%.*]]
+; SKIP0-COUNT1:       bb2:
+; SKIP0-COUNT1-NEXT:    br label [[BB3]]
+; SKIP0-COUNT1:       bb3:
+; SKIP0-COUNT1-NEXT:    store i32 0, i32* [[Q:%.*]]
+; SKIP0-COUNT1-NEXT:    store i32 0, i32* [[R:%.*]]
+; SKIP0-COUNT1-NEXT:    store i32 0, i32* [[P]]
+; SKIP0-COUNT1-NEXT:    ret void
+;
+; SKIP1-COUNT1-LABEL: @test(
+; SKIP1-COUNT1-NEXT:    store i32 1, i32* [[R:%.*]]
+; SKIP1-COUNT1-NEXT:    br i1 true, label [[BB1:%.*]], label [[BB2:%.*]]
+; SKIP1-COUNT1:       bb1:
+; SKIP1-COUNT1-NEXT:    br label [[BB3:%.*]]
+; SKIP1-COUNT1:       bb2:
+; SKIP1-COUNT1-NEXT:    br label [[BB3]]
+; SKIP1-COUNT1:       bb3:
+; SKIP1-COUNT1-NEXT:    store i32 0, i32* [[Q:%.*]]
+; SKIP1-COUNT1-NEXT:    store i32 0, i32* [[R]]
+; SKIP1-COUNT1-NEXT:    store i32 0, i32* [[P:%.*]]
+; SKIP1-COUNT1-NEXT:    ret void
+;
+; SKIP0-COUNT2-LABEL: @test(
+; SKIP0-COUNT2-NEXT:    br i1 true, label [[BB1:%.*]], label [[BB2:%.*]]
+; SKIP0-COUNT2:       bb1:
+; SKIP0-COUNT2-NEXT:    br label [[BB3:%.*]]
+; SKIP0-COUNT2:       bb2:
+; SKIP0-COUNT2-NEXT:    br label [[BB3]]
+; SKIP0-COUNT2:       bb3:
+; SKIP0-COUNT2-NEXT:    store i32 0, i32* [[Q:%.*]]
+; SKIP0-COUNT2-NEXT:    store i32 0, i32* [[R:%.*]]
+; SKIP0-COUNT2-NEXT:    store i32 0, i32* [[P:%.*]]
+; SKIP0-COUNT2-NEXT:    ret void
+;
+; SKIP2-COUNT1-LABEL: @test(
+; SKIP2-COUNT1-NEXT:    store i32 1, i32* [[P:%.*]]
+; SKIP2-COUNT1-NEXT:    store i32 1, i32* [[R:%.*]]
+; SKIP2-COUNT1-NEXT:    br i1 true, label [[BB1:%.*]], label [[BB2:%.*]]
+; SKIP2-COUNT1:       bb1:
+; SKIP2-COUNT1-NEXT:    br label [[BB3:%.*]]
+; SKIP2-COUNT1:       bb2:
+; SKIP2-COUNT1-NEXT:    br label [[BB3]]
+; SKIP2-COUNT1:       bb3:
+; SKIP2-COUNT1-NEXT:    store i32 0, i32* [[Q:%.*]]
+; SKIP2-COUNT1-NEXT:    store i32 0, i32* [[R]]
+; SKIP2-COUNT1-NEXT:    store i32 0, i32* [[P]]
+; SKIP2-COUNT1-NEXT:    ret void
+;
+  store i32 1, i32* %P
+  store i32 1, i32* %R
+  br i1 true, label %bb1, label %bb2
+bb1:
+  br label %bb3
+bb2:
+  br label %bb3
+bb3:
+  store i32 0, i32* %Q
+  store i32 0, i32* %R
+  store i32 0, i32* %P
+  ret void
+}