[PATCH] StructurizeCFG: Use LoopInfo analysis for better loop detection

[Michael Ilseman]

Have you considered requiring Loop Simplify? Loop Simplify, IIRC, will pull in LoopInfo. I don’t know your particular situation, but it can be useful especially if you’re already doing this based on regions and a relatively canonicalize CFG.


> On Nov 14, 2014, at 12:01 PM, Tom Stellard <thomas.stellard at amd.com> wrote:
> 
> We were assuming that each back-edge in a region represented a unique
> loop, which is not always the case.  We need to use LoopInfo to
> correctly determine which back-edges are loops.
> ---
> lib/Transforms/Scalar/StructurizeCFG.cpp           |  7 +++-
> .../StructurizeCFG/one-loop-multiple-backedges.ll  | 41 ++++++++++++++++++++++
> 2 files changed, 47 insertions(+), 1 deletion(-)
> create mode 100644 test/Transforms/StructurizeCFG/one-loop-multiple-backedges.ll
> 
> diff --git a/lib/Transforms/Scalar/StructurizeCFG.cpp b/lib/Transforms/Scalar/StructurizeCFG.cpp
> index b9673ed..7fe87f9 100644
> --- a/lib/Transforms/Scalar/StructurizeCFG.cpp
> +++ b/lib/Transforms/Scalar/StructurizeCFG.cpp
> @@ -10,6 +10,7 @@
> #include "llvm/Transforms/Scalar.h"
> #include "llvm/ADT/MapVector.h"
> #include "llvm/ADT/SCCIterator.h"
> +#include "llvm/Analysis/LoopInfo.h"
> #include "llvm/Analysis/RegionInfo.h"
> #include "llvm/Analysis/RegionIterator.h"
> #include "llvm/Analysis/RegionPass.h"
> @@ -166,6 +167,7 @@ class StructurizeCFG : public RegionPass {
>   Region *ParentRegion;
> 
>   DominatorTree *DT;
> +  LoopInfo *LI;
> 
>   RNVector Order;
>   BBSet Visited;
> @@ -247,6 +249,7 @@ public:
>   void getAnalysisUsage(AnalysisUsage &AU) const override {
>     AU.addRequiredID(LowerSwitchID);
>     AU.addRequired<DominatorTreeWrapperPass>();
> +    AU.addRequired<LoopInfo>();
>     AU.addPreserved<DominatorTreeWrapperPass>();
>     RegionPass::getAnalysisUsage(AU);
>   }
> @@ -301,8 +304,9 @@ void StructurizeCFG::analyzeLoops(RegionNode *N) {
>     for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
>       BasicBlock *Succ = Term->getSuccessor(i);
> 
> -      if (Visited.count(Succ))
> +      if (Visited.count(Succ) && LI->isLoopHeader(Succ) ) {
>         Loops[Succ] = BB;
> +      }
>     }
>   }
> }
> @@ -862,6 +866,7 @@ bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
>   ParentRegion = R;
> 
>   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
> +  LI = &getAnalysis<LoopInfo>();
> 
>   orderNodes();
>   collectInfos();
> diff --git a/test/Transforms/StructurizeCFG/one-loop-multiple-backedges.ll b/test/Transforms/StructurizeCFG/one-loop-multiple-backedges.ll
> new file mode 100644
> index 0000000..8ebd47a
> --- /dev/null
> +++ b/test/Transforms/StructurizeCFG/one-loop-multiple-backedges.ll
> @@ -0,0 +1,41 @@
> +; RUN: opt -S -structurizecfg %s -o - | FileCheck %s
> +
> +; CHECK-NOT: br i1 true
> +
> +define void @blam(i32 addrspace(1)* nocapture %arg, float %arg1, float %arg2) {
> +; CHECK: bb:
> +bb:
> +  br label %bb3
> +
> +; CHECK: bb3:
> +bb3:                                              ; preds = %bb7, %bb
> +  %tmp = phi i64 [ 0, %bb ], [ %tmp8, %bb7 ]
> +  %tmp4 = fcmp ult float %arg1, 3.500000e+00
> +; CHECK: br i1 %tmp4, label %bb7, label %Flow
> +  br i1 %tmp4, label %bb7, label %bb5
> +
> +; CHECK: Flow:
> +; CHECK: br i1 %2, label %Flow1, label %bb3
> +
> +; CHECK: Flow1:
> +; CHECK: br i1 %3, label %bb5, label %bb10
> +
> +; CHECK: bb5:
> +bb5:                                              ; preds = %bb3
> +  %tmp6 = fcmp olt float 0.000000e+00, %arg2
> +; CHECK: br label %bb10
> +  br i1 %tmp6, label %bb10, label %bb7
> +
> +; CHECK: bb7
> +bb7:                                              ; preds = %bb5, %bb3
> +  %tmp8 = add nuw nsw i64 %tmp, 1
> +  %tmp9 = icmp slt i64 %tmp8, 5
> +; CHECK: br label %Flow
> +  br i1 %tmp9, label %bb3, label %bb10
> +
> +; CHECK: bb10
> +bb10:                                             ; preds = %bb7, %bb5
> +  %tmp11 = phi i32 [ 15, %bb5 ], [ 255, %bb7 ]
> +  store i32 %tmp11, i32 addrspace(1)* %arg, align 4
> +  ret void
> +}
> -- 
> 1.8.5.5
> 
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