Added debug counter and new test

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 {
@@ -690,7 +694,8 @@ bool StraightLineStrengthReduce::runOnFunction(Function &F) {
   while (!Candidates.empty()) {
     const Candidate &C = Candidates.back();
     if (C.Basis != nullptr) {
-      rewriteCandidateWithBasis(C, *C.Basis);
+      if (DebugCounter::shouldExecute(StraightLineStrengthReduceCounter))
+        rewriteCandidateWithBasis(C, *C.Basis);
     }
     Candidates.pop_back();
   }

llvm/test/Other/debugcounter-slsr.ll

@@ -0,0 +1,30 @@
+; REQUIRES: asserts
+; RUN: opt -passes=slsr,gvn -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:    %t2 = add i32 %t1, %s2
+; CHECK-NEXT:    call void @foo(i32 %t2)
+; CHECK-NEXT:    %s6 = mul i32 %s, 6
+; CHECK-NEXT:    %t3 = add i32 %b, %s6
+; CHECK-NEXT:    call void @foo(i32 %t3)
+; 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)
+  %s6 = mul i32 %s, 6
+  %t3 = add i32 %b, %s6
+  call void @foo(i32 %t3)
+  ret void
+}
+
+declare void @foo(i32)