[LLVM][SLSR] Add a debug counter (llvm#119981)

Added debug counter and test for SLSR.

Fixes: llvm#119770

Author: GrumpyPigSkin

llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp

@@ -78,6 +78,7 @@
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/DebugCounter.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -93,6 +94,9 @@ using namespace PatternMatch;
 static const unsigned UnknownAddressSpace =
     std::numeric_limits<unsigned>::max();
 
+DEBUG_COUNTER(StraightLineStrengthReduceCounter, "slsr-counter",
+              "Controls whether rewriteCandidateWithBasis is executed.");
+
 namespace {
 
 class StraightLineStrengthReduceLegacyPass : public FunctionPass {
@@ -268,8 +272,8 @@ FunctionPass *llvm::createStraightLineStrengthReducePass() {
 bool StraightLineStrengthReduce::isBasisFor(const Candidate &Basis,
                                             const Candidate &C) {
   return (Basis.Ins != C.Ins && // skip the same instruction
-          // They must have the same type too. Basis.Base == C.Base doesn't
-          // guarantee their types are the same (PR23975).
+          // They must have the same type too. Basis.Base == C.Base
+          // doesn't guarantee their types are the same (PR23975).
           Basis.Ins->getType() == C.Ins->getType() &&
           // Basis must dominate C in order to rewrite C with respect to Basis.
           DT->dominates(Basis.Ins->getParent(), C.Ins->getParent()) &&
@@ -610,6 +614,9 @@ Value *StraightLineStrengthReduce::emitBump(const Candidate &Basis,
 
 void StraightLineStrengthReduce::rewriteCandidateWithBasis(
     const Candidate &C, const Candidate &Basis) {
+  if (!DebugCounter::shouldExecute(StraightLineStrengthReduceCounter))
+    return;
+
   assert(C.CandidateKind == Basis.CandidateKind && C.Base == Basis.Base &&
          C.Stride == Basis.Stride);
   // We run rewriteCandidateWithBasis on all candidates in a post-order, so the

llvm/test/Other/debugcounter-slsr.ll

@@ -0,0 +1,26 @@
+; REQUIRES: asserts
+; RUN: opt -passes=slsr -S -debug-counter=slsr-counter=1  < %s | FileCheck %s
+
+; Test that, with debug counters on, we will skip the first slsr opportunity.
+
+define void @stride_is_2s(i32 %b, i32 %s) {
+; CHECK-LABEL: @stride_is_2s(
+; CHECK-NEXT: %s2 = shl i32 %s, 1
+; CHECK-NEXT: %t1 = add i32 %b, %s2
+; CHECK-NEXT: call void @foo(i32 %t1)
+; CHECK-NEXT: %s4 = shl i32 %s, 2
+; CHECK-NEXT: %t2 = add i32 %b, %s4
+; CHECK-NEXT: call void @foo(i32 %t2)
+; CHECK-NEXT: ret void
+;
+  %s2 = shl i32 %s, 1
+  %t1 = add i32 %b, %s2
+  call void @foo(i32 %t1)
+  %s4 = shl i32 %s, 2
+  %t2 = add i32 %b, %s4
+  call void @foo(i32 %t2)
+  ret void
+}
+
+declare void @foo(i32)
+