[llvm] r272224 - [LoopSimplify] Preserve LCSSA when merging exit blocks.

Mikael Holmén via llvm-commits llvm-commits at lists.llvm.org
Wed Jun 22 01:25:34 PDT 2016


Hi Michael,

The checks introduced in this commit fail on:

opt -S -lcssa -loop-unroll red.ll

I don't know if it's the checks or the optimization that is actually wrong.

Regards,
Mikael

On 06/09/2016 01:13 AM, Michael Zolotukhin via llvm-commits wrote:
> Author: mzolotukhin
> Date: Wed Jun  8 18:13:21 2016
> New Revision: 272224
>
> URL: http://llvm.org/viewvc/llvm-project?rev=272224&view=rev
> Log:
> [LoopSimplify] Preserve LCSSA when merging exit blocks.
>
> Summary:
> This fixes PR26682. Also add LCSSA as a preserved pass to LoopSimplify,
> that looks correct to me and allows to write a test for the issue.
>
> Reviewers: chandlerc, bogner, sanjoy
>
> Subscribers: llvm-commits
>
> Differential Revision: http://reviews.llvm.org/D21112
>
> Added:
>      llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll
> Modified:
>      llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
>
> Modified: llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp?rev=272224&r1=272223&r2=272224&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp Wed Jun  8 18:13:21 2016
> @@ -686,8 +686,10 @@ ReprocessLoop:
>         }
>         DT->eraseNode(ExitingBlock);
>
> -      BI->getSuccessor(0)->removePredecessor(ExitingBlock);
> -      BI->getSuccessor(1)->removePredecessor(ExitingBlock);
> +      BI->getSuccessor(0)->removePredecessor(
> +          ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
> +      BI->getSuccessor(1)->removePredecessor(
> +          ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
>         ExitingBlock->eraseFromParent();
>       }
>     }
> @@ -748,6 +750,7 @@ namespace {
>         AU.addPreserved<GlobalsAAWrapperPass>();
>         AU.addPreserved<ScalarEvolutionWrapperPass>();
>         AU.addPreserved<SCEVAAWrapperPass>();
> +      AU.addPreservedID(LCSSAID);
>         AU.addPreserved<DependenceAnalysisWrapperPass>();
>         AU.addPreservedID(BreakCriticalEdgesID);  // No critical edges added.
>       }
> @@ -781,11 +784,27 @@ bool LoopSimplify::runOnFunction(Functio
>     SE = SEWP ? &SEWP->getSE() : nullptr;
>     AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
>     bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
> +#ifndef NDEBUG
> +  if (PreserveLCSSA) {
> +    assert(DT && "DT not available.");
> +    assert(LI && "LI not available.");
> +    bool InLCSSA =
> +        all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
> +    assert(InLCSSA && "Requested to preserve LCSSA, but it's already broken.");
> +  }
> +#endif
>
>     // Simplify each loop nest in the function.
>     for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
>       Changed |= simplifyLoop(*I, DT, LI, SE, AC, PreserveLCSSA);
>
> +#ifndef NDEBUG
> +  if (PreserveLCSSA) {
> +    bool InLCSSA =
> +        all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
> +    assert(InLCSSA && "LCSSA is broken after loop-simplify.");
> +  }
> +#endif
>     return Changed;
>   }
>
>
> Added: llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll?rev=272224&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll (added)
> +++ llvm/trunk/test/Transforms/LoopSimplify/pr26682.ll Wed Jun  8 18:13:21 2016
> @@ -0,0 +1,32 @@
> +; RUN: opt < %s -lcssa -loop-simplify -indvars -S | FileCheck %s
> +target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
> +target triple = "x86_64-unknown-unknown"
> +
> + at a = external global i32, align 4
> +
> +; Check that loop-simplify merges two loop exits, but preserves LCSSA form.
> +; CHECK-LABEL: @foo
> +; CHECK: for:
> +; CHECK: %or.cond = and i1 %cmp1, %cmp2
> +; CHECK-NOT: for.cond:
> +; CHECK: for.end:
> +; CHECK: %a.lcssa = phi i32 [ %a, %for ]
> +define i32 @foo(i32 %x) {
> +entry:
> +  br label %for
> +
> +for:
> +  %iv = phi i32 [ 0, %entry ], [ %iv.next, %for.cond ]
> +  %cmp1 = icmp eq i32 %x, 0
> +  %iv.next = add nuw nsw i32 %iv, 1
> +  %a = load i32, i32* @a
> +  br i1 %cmp1, label %for.cond, label %for.end
> +
> +for.cond:
> +  %cmp2 = icmp slt i32 %iv.next, 4
> +  br i1 %cmp2, label %for, label %for.end
> +
> +for.end:
> +  %a.lcssa = phi i32 [ %a, %for ], [ %a, %for.cond ]
> +  ret i32 %a.lcssa
> +}
>
>
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-------------- next part --------------
; ModuleID = 'bugpoint-reduced-simplified.bc'
source_filename = "red.ll"
target triple = "x86_64-unknown-linux-gnu"

declare i32 @safe_div_func_uint32_t_u_u()

define void @func_10() {
  br label %bb1

bb1:                                              ; preds = %bb1, %0
  br i1 undef, label %bb1, label %bb29

bb40:                                             ; preds = %bb29, %bb40
  br i1 undef, label %bb40, label %bb43

bb43:                                             ; preds = %bb54, %bb45, %bb40
  %l_976.193.0 = phi i32 [ undef, %bb40 ], [ 0, %bb45 ], [ %l_976.193.0, %bb54 ]
  %l_934.130.0 = phi i32 [ 0, %bb40 ], [ %_tmp862, %bb54 ], [ %_tmp862, %bb45 ]
  br i1 undef, label %bb114, label %bb29

bb114:                                            ; preds = %bb43
  %_tmp862 = call i32 @safe_div_func_uint32_t_u_u()
  br i1 undef, label %bb45, label %bb54

bb45:                                             ; preds = %bb114
  br label %bb43

bb54:                                             ; preds = %bb114
  br label %bb43

bb71:                                             ; preds = %bb29
  ret void

bb29:                                             ; preds = %bb43, %bb1
  br i1 undef, label %bb40, label %bb71
}


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