[StructurizeCFG] Convert legacy pass from RegionPass to FunctionPass (#233940)

Convert StructurizeCFGLegacyPass from a RegionPass to a FunctionPass,
just like the NewPM version.

Possible follow-ups:
- Stop using metadata to propagate information from inner to outer
  regions.
- Remove RegionPass and RGPassManager from LLVM.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

llvm/lib/Transforms/Scalar/StructurizeCFG.cpp

@@ -18,7 +18,6 @@
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/RegionInfo.h"
 #include "llvm/Analysis/RegionIterator.h"
-#include "llvm/Analysis/RegionPass.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/UniformityAnalysis.h"
 #include "llvm/IR/BasicBlock.h"
@@ -360,34 +359,18 @@ public:
   bool makeUniformRegion(Region *R, UniformityInfo &UA);
 };
 
-class StructurizeCFGLegacyPass : public RegionPass {
+class StructurizeCFGLegacyPass : public FunctionPass {
   bool SkipUniformRegions;
 
 public:
   static char ID;
 
   explicit StructurizeCFGLegacyPass(bool SkipUniformRegions_ = false)
-      : RegionPass(ID), SkipUniformRegions(SkipUniformRegions_) {
+      : FunctionPass(ID), SkipUniformRegions(SkipUniformRegions_) {
     initializeStructurizeCFGLegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
-  bool runOnRegion(Region *R, RGPassManager &RGM) override {
-    StructurizeCFG SCFG;
-    SCFG.init(R);
-    const ScalarOptions &Opts =
-        R->getEntry()->getContext().getLibraryOptions().get<ScalarOptions>();
-    if (valueOr(Opts.structurizecfg_skip_uniform_regions, SkipUniformRegions)) {
-      UniformityInfo &UA =
-          getAnalysis<UniformityInfoWrapperPass>().getUniformityInfo();
-      if (SCFG.makeUniformRegion(R, UA))
-        return false;
-    }
-    Function *F = R->getEntry()->getParent();
-    const TargetTransformInfo *TTI =
-        &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(*F);
-    DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
-    return SCFG.run(R, DT, TTI);
-  }
+  bool runOnFunction(Function &F) override;
 
   StringRef getPassName() const override { return "Structurize control flow"; }
 
@@ -395,9 +378,9 @@ public:
     AU.addRequired<UniformityInfoWrapperPass>();
     AU.addRequired<DominatorTreeWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
+    AU.addRequired<RegionInfoPass>();
 
     AU.addPreserved<DominatorTreeWrapperPass>();
-    RegionPass::getAnalysisUsage(AU);
   }
 };
 
@@ -1407,21 +1390,11 @@ void StructurizeCFGPass::printPipeline(
     OS << "<skip-uniform-regions>";
 }
 
-PreservedAnalyses StructurizeCFGPass::run(Function &F,
-                                          FunctionAnalysisManager &AM) {
-
+/// Structurize every region in \p RI, processing inner regions before the
+/// regions that contain them. If \p UI is non-null, skip uniform regions.
+static bool runImpl(DominatorTree &DT, RegionInfo &RI,
+                    const TargetTransformInfo &TTI, UniformityInfo *UI) {
   bool Changed = false;
-  DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
-  auto &RI = AM.getResult<RegionInfoAnalysis>(F);
-  TargetTransformInfo *TTI = &AM.getResult<TargetIRAnalysis>(F);
-  const ScalarOptions &Opts =
-      F.getContext().getLibraryOptions().get<ScalarOptions>();
-  bool SkipUniform =
-      valueOr(Opts.structurizecfg_skip_uniform_regions, SkipUniformRegions);
-  UniformityInfo *UI = nullptr;
-  if (SkipUniform)
-    UI = &AM.getResult<UniformityInfoAnalysis>(F);
-
   std::vector<Region *> Regions;
   addRegionIntoQueue(*RI.getTopLevelRegion(), Regions);
   while (!Regions.empty()) {
@@ -1431,14 +1404,41 @@ PreservedAnalyses StructurizeCFGPass::run(Function &F,
     StructurizeCFG SCFG;
     SCFG.init(R);
 
-    if (SkipUniform && SCFG.makeUniformRegion(R, *UI)) {
+    if (UI && SCFG.makeUniformRegion(R, *UI)) {
       Changed = true; // May have added metadata.
       continue;
     }
 
-    Changed |= SCFG.run(R, DT, TTI);
+    Changed |= SCFG.run(R, &DT, &TTI);
   }
-  if (!Changed)
+  return Changed;
+}
+
+bool StructurizeCFGLegacyPass::runOnFunction(Function &F) {
+  const ScalarOptions &Opts =
+      F.getContext().getLibraryOptions().get<ScalarOptions>();
+  UniformityInfo *UI = nullptr;
+  if (valueOr(Opts.structurizecfg_skip_uniform_regions, SkipUniformRegions))
+    UI = &getAnalysis<UniformityInfoWrapperPass>().getUniformityInfo();
+  DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  RegionInfo &RI = getAnalysis<RegionInfoPass>().getRegionInfo();
+  const TargetTransformInfo &TTI =
+      getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+  return runImpl(DT, RI, TTI, UI);
+}
+
+PreservedAnalyses StructurizeCFGPass::run(Function &F,
+                                          FunctionAnalysisManager &AM) {
+  DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
+  auto &RI = AM.getResult<RegionInfoAnalysis>(F);
+  TargetTransformInfo &TTI = AM.getResult<TargetIRAnalysis>(F);
+  const ScalarOptions &Opts =
+      F.getContext().getLibraryOptions().get<ScalarOptions>();
+  UniformityInfo *UI = nullptr;
+  if (valueOr(Opts.structurizecfg_skip_uniform_regions, SkipUniformRegions))
+    UI = &AM.getResult<UniformityInfoAnalysis>(F);
+
+  if (!runImpl(DT, RI, TTI, UI))
     return PreservedAnalyses::all();
   PreservedAnalyses PA;
   PA.preserve<DominatorTreeAnalysis>();

llvm/test/CodeGen/AMDGPU/llc-pipeline.ll

@@ -70,8 +70,7 @@
 ; GCN-O0-NEXT:      Post-Dominator Tree Construction
 ; GCN-O0-NEXT:      Dominance Frontier Construction
 ; GCN-O0-NEXT:      Detect single entry single exit regions
-; GCN-O0-NEXT:      Region Pass Manager
-; GCN-O0-NEXT:        Structurize control flow
+; GCN-O0-NEXT:      Structurize control flow
 ; GCN-O0-NEXT:      Cycle Info Analysis
 ; GCN-O0-NEXT:      Uniformity Analysis
 ; GCN-O0-NEXT:      Basic Alias Analysis (stateless AA impl)
@@ -279,8 +278,7 @@
 ; GCN-O1-NEXT:      Post-Dominator Tree Construction
 ; GCN-O1-NEXT:      Dominance Frontier Construction
 ; GCN-O1-NEXT:      Detect single entry single exit regions
-; GCN-O1-NEXT:      Region Pass Manager
-; GCN-O1-NEXT:        Structurize control flow
+; GCN-O1-NEXT:      Structurize control flow
 ; GCN-O1-NEXT:      Cycle Info Analysis
 ; GCN-O1-NEXT:      Uniformity Analysis
 ; GCN-O1-NEXT:      Basic Alias Analysis (stateless AA impl)
@@ -600,8 +598,7 @@
 ; GCN-O1-OPTS-NEXT:      Post-Dominator Tree Construction
 ; GCN-O1-OPTS-NEXT:      Dominance Frontier Construction
 ; GCN-O1-OPTS-NEXT:      Detect single entry single exit regions
-; GCN-O1-OPTS-NEXT:      Region Pass Manager
-; GCN-O1-OPTS-NEXT:        Structurize control flow
+; GCN-O1-OPTS-NEXT:      Structurize control flow
 ; GCN-O1-OPTS-NEXT:      Cycle Info Analysis
 ; GCN-O1-OPTS-NEXT:      Uniformity Analysis
 ; GCN-O1-OPTS-NEXT:      Basic Alias Analysis (stateless AA impl)
@@ -932,8 +929,7 @@
 ; GCN-O2-NEXT:      Post-Dominator Tree Construction
 ; GCN-O2-NEXT:      Dominance Frontier Construction
 ; GCN-O2-NEXT:      Detect single entry single exit regions
-; GCN-O2-NEXT:      Region Pass Manager
-; GCN-O2-NEXT:        Structurize control flow
+; GCN-O2-NEXT:      Structurize control flow
 ; GCN-O2-NEXT:      Cycle Info Analysis
 ; GCN-O2-NEXT:      Uniformity Analysis
 ; GCN-O2-NEXT:      Basic Alias Analysis (stateless AA impl)
@@ -1281,8 +1277,7 @@
 ; GCN-O3-NEXT:      Post-Dominator Tree Construction
 ; GCN-O3-NEXT:      Dominance Frontier Construction
 ; GCN-O3-NEXT:      Detect single entry single exit regions
-; GCN-O3-NEXT:      Region Pass Manager
-; GCN-O3-NEXT:        Structurize control flow
+; GCN-O3-NEXT:      Structurize control flow
 ; GCN-O3-NEXT:      Cycle Info Analysis
 ; GCN-O3-NEXT:      Uniformity Analysis
 ; GCN-O3-NEXT:      Basic Alias Analysis (stateless AA impl)