[PATCH] [OPENMP] llvm.loop.vectorize.enable metadata are lost after critical edge splitting
Johannes Doerfert
doerfert at cs.uni-saarland.de
Tue Sep 30 06:11:01 PDT 2014
I'm not completely sure but this sounds similar to what I did a couple
of weeks ago (http://reviews.llvm.org/D5344) however I didn't force
LoopInfo to be present but rather handled the case it isn't. For the
record, I don't know the benefits/drawbacks for either.
If we use your patch we could possibly add my test cases.
On 09/30, Zinovy Nis wrote:
> Hi chandlerc, atrick,
>
> Critical edge splitting called by GVN and Loop Rotation leads to losing of ```llvm.loop.vectorize.enable``` metadata for loops as critical edge splitting replaces a branch, corresponding to the loop latch, with a new one.
>
> My patch clones loop latch metadata to a new latch branch thus fixing the issue.
>
> I also had to add LoopInfo analysis for GVN, as it's needed for latch metadata cloning.
>
> http://reviews.llvm.org/D5539
>
> Files:
> lib/Transforms/Scalar/GVN.cpp
> lib/Transforms/Utils/BreakCriticalEdges.cpp
> test/Transforms/LoopVectorize/vect.omp.persistence.gvn.ll
> Index: lib/Transforms/Scalar/GVN.cpp
> ===================================================================
> --- lib/Transforms/Scalar/GVN.cpp
> +++ lib/Transforms/Scalar/GVN.cpp
> @@ -48,6 +48,7 @@
> #include "llvm/Transforms/Utils/BasicBlockUtils.h"
> #include "llvm/Transforms/Utils/Local.h"
> #include "llvm/Transforms/Utils/SSAUpdater.h"
> +#include "llvm/Analysis/LoopPass.h"
> #include <vector>
> using namespace llvm;
> using namespace PatternMatch;
> @@ -691,6 +692,7 @@
>
> AU.addPreserved<DominatorTreeWrapperPass>();
> AU.addPreserved<AliasAnalysis>();
> + AU.addRequired<LoopInfo>();
> }
>
>
> @@ -736,6 +738,7 @@
> INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
> INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
> INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
> +INITIALIZE_PASS_DEPENDENCY(LoopInfo)
> INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false)
>
> #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
> Index: lib/Transforms/Utils/BreakCriticalEdges.cpp
> ===================================================================
> --- lib/Transforms/Utils/BreakCriticalEdges.cpp
> +++ lib/Transforms/Utils/BreakCriticalEdges.cpp
> @@ -150,6 +150,14 @@
> BasicBlock *TIBB = TI->getParent();
> BasicBlock *DestBB = TI->getSuccessor(SuccNum);
>
> + LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : nullptr;
> +
> + Loop *TIBBLoop = LI ? LI->getLoopFor(TIBB) : nullptr;
> + Loop *DestBBLoop = LI ? LI->getLoopFor(DestBB) : nullptr;
> +
> + MDNode *TILoopMD = TIBBLoop ? TIBBLoop->getLoopID() : nullptr;
> + MDNode *DestLoopMD = DestBBLoop ? DestBBLoop->getLoopID() : nullptr;
> +
> // Splitting the critical edge to a landing pad block is non-trivial. Don't do
> // it in this generic function.
> if (DestBB->isLandingPad()) return nullptr;
> @@ -205,15 +213,12 @@
> }
> }
>
> -
> -
> // If we don't have a pass object, we can't update anything...
> if (!P) return NewBB;
>
> DominatorTreeWrapperPass *DTWP =
> P->getAnalysisIfAvailable<DominatorTreeWrapperPass>();
> DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
> - LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();
>
> // If we have nothing to update, just return.
> if (!DT && !LI)
> @@ -351,6 +356,12 @@
> "SplitCriticalEdge doesn't know how to update LCCSA form "
> "without LoopSimplify!");
> }
> + // Loop metadata are stored in the loop latch branch.
> + // If loops latches were changed let's update new latches metadata.
> + if (TILoopMD)
> + TIBBLoop->setLoopID(TILoopMD);
> + if (DestLoopMD && DestBBLoop != TIBBLoop)
> + DestBBLoop->setLoopID(DestLoopMD);
> }
>
> return NewBB;
> Index: test/Transforms/LoopVectorize/vect.omp.persistence.gvn.ll
> ===================================================================
> --- /dev/null
> +++ test/Transforms/LoopVectorize/vect.omp.persistence.gvn.ll
> @@ -0,0 +1,41 @@
> +; RUN: opt < %s -basicaa -gvn -S 2>&1 | FileCheck %s
> +
> +; CHECK-LABEL: @test_gvn
> +; CHECK-LABEL: for.body:
> +; Find a branch to critical edge
> +; CHECK: br {{.*}} %[[CE:[^_ ]+]]_crit_edge
> +; BB where critical edge was found
> +; CHECK: [[CE]]_crit_edge:
> +; Check that OMP SIMD branch metadata survived after critical edge splitting
> +; CHECK: br label %for.body, !llvm.loop !0
> +
> +target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
> +target triple = "x86_64-unknown-linux-gnu"
> +
> +;
> +; Ensure that "llvm.loop.vectorize.enable" metadata were not lost after GVN splitted critical edges.
> +; In past splitting critical edges was leading to clearing that metadata.
> +;
> +
> +define i64 @test_gvn(i64* nocapture readonly %a, i64* nocapture readonly %b) {
> +entry:
> + %0 = load i64* %b, align 4, !llvm.mem.parallel_loop_access !0
> + br label %for.body
> +for.body:
> + %i.0 = phi i64 [ 0, %entry ], [ %inc, %for.body ]
> + %arrayidx = getelementptr inbounds i64* %a, i64 %i.0
> + %1 = load i64* %arrayidx, align 4, !llvm.mem.parallel_loop_access !1
> + %arrayidx2 = getelementptr inbounds i64* %b, i64 %i.0
> + %2 = load i64* %arrayidx2, align 4, !llvm.mem.parallel_loop_access !1
> + %cmp3 = icmp sgt i64 %1, %2
> + %add16 = select i1 %cmp3, i64 0, i64 %2
> + %inc = add nsw i64 %i.0, 1
> + %add = add nsw i64 %0, %inc
> + %cmp = icmp slt i64 %i.0, %add
> + br i1 %cmp, label %for.body, label %for.end, !llvm.loop !0
> +for.end:
> + ret i64 %inc
> +}
> +
> +!0 = metadata !{metadata !0, metadata !1}
> +!1 = metadata !{metadata !"llvm.loop.vectorize.enable", i1 true}
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--
Johannes Doerfert
Researcher / PhD Student
Compiler Design Lab (Prof. Hack)
Saarland University, Computer Science
Building E1.3, Room 4.26
Tel. +49 (0)681 302-57521 : doerfert at cs.uni-saarland.de
Fax. +49 (0)681 302-3065 : http://www.cdl.uni-saarland.de/people/doerfert
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