[llvm] r210721 - Teach LoopUnrollPass to respect loop unrolling hints in metadata.

David Blaikie dblaikie at gmail.com
Wed Jun 11 21:43:14 PDT 2014


I think this may've broken some things... a few of our internal tests
are failing, and one of the GDB tester's tests is segfaulting (
http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/15423
) - mind taking a look/reverting? Let me know if you'd like more
specific reproductions, steps, etc.

On Wed, Jun 11, 2014 at 4:15 PM, Eli Bendersky <eliben at google.com> wrote:
> Author: eliben
> Date: Wed Jun 11 18:15:35 2014
> New Revision: 210721
>
> URL: http://llvm.org/viewvc/llvm-project?rev=210721&view=rev
> Log:
> Teach LoopUnrollPass to respect loop unrolling hints in metadata.
>
> See http://reviews.llvm.org/D4090 for more details.
>
> The Clang change that produces this metadata was committed in r210667
>
> Patch by Mark Heffernan.
>
>
> Added:
>     llvm/trunk/test/Transforms/LoopUnroll/unroll-pragmas.ll
> Modified:
>     llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp?rev=210721&r1=210720&r2=210721&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp Wed Jun 11 18:15:35 2014
> @@ -20,6 +20,7 @@
>  #include "llvm/IR/DataLayout.h"
>  #include "llvm/IR/Dominators.h"
>  #include "llvm/IR/IntrinsicInst.h"
> +#include "llvm/IR/Metadata.h"
>  #include "llvm/Support/CommandLine.h"
>  #include "llvm/Support/Debug.h"
>  #include "llvm/Support/raw_ostream.h"
> @@ -36,7 +37,8 @@ UnrollThreshold("unroll-threshold", cl::
>
>  static cl::opt<unsigned>
>  UnrollCount("unroll-count", cl::init(0), cl::Hidden,
> -  cl::desc("Use this unroll count for all loops, for testing purposes"));
> +  cl::desc("Use this unroll count for all loops including those with "
> +           "unroll_count pragma values, for testing purposes"));
>
>  static cl::opt<bool>
>  UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
> @@ -47,6 +49,13 @@ static cl::opt<bool>
>  UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden,
>    cl::desc("Unroll loops with run-time trip counts"));
>
> +// Maximum allowed unroll count for a loop being fully unrolled
> +// because of a pragma unroll(enable) statement (ie, metadata
> +// "llvm.loopunroll.enable" is true).  This prevents unexpected
> +// behavior like crashing when using this pragma on high trip count
> +// loops.
> +static const unsigned PragmaFullUnrollCountLimit = 1024;
> +
>  namespace {
>    class LoopUnroll : public LoopPass {
>    public:
> @@ -151,6 +160,63 @@ static unsigned ApproximateLoopSize(cons
>    return LoopSize;
>  }
>
> +// Returns the value associated with the given metadata node name (for
> +// example, "llvm.loopunroll.count").  If no such named metadata node
> +// exists, then nullptr is returned.
> +static const ConstantInt *GetUnrollMetadataValue(const Loop *L,
> +                                                 StringRef Name) {
> +  MDNode *LoopID = L->getLoopID();
> +  if (!LoopID) return nullptr;
> +
> +  // First operand should refer to the loop id itself.
> +  assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
> +  assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
> +
> +  for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
> +    const MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
> +    if (!MD) continue;
> +
> +    const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
> +    if (!S) continue;
> +
> +    if (Name.equals(S->getString())) {
> +      assert(MD->getNumOperands() == 2 &&
> +             "Unroll hint metadata should have two operands.");
> +      return cast<ConstantInt>(MD->getOperand(1));
> +    }
> +  }
> +  return nullptr;
> +}
> +
> +// Returns true if the loop has an unroll(enable) pragma.
> +static bool HasUnrollEnablePragma(const Loop *L) {
> +  const ConstantInt *EnableValue =
> +      GetUnrollMetadataValue(L, "llvm.loopunroll.enable");
> +  return (EnableValue && EnableValue->getZExtValue());
> +  return false;
> +}
> +
> +// Returns true if the loop has an unroll(disable) pragma.
> +static bool HasUnrollDisablePragma(const Loop *L) {
> +  const ConstantInt *EnableValue =
> +      GetUnrollMetadataValue(L, "llvm.loopunroll.enable");
> +  return (EnableValue && !EnableValue->getZExtValue());
> +  return false;
> +}
> +
> +// Check for unroll_count(N) pragma.  If found, return true and set
> +// Count to the integer parameter of the pragma.
> +static bool HasUnrollCountPragma(const Loop *L, int &Count) {
> +  const ConstantInt *CountValue =
> +      GetUnrollMetadataValue(L, "llvm.loopunroll.count");
> +  if (CountValue) {
> +    Count = CountValue->getZExtValue();
> +    assert(Count >= 1 && "Unroll count must be positive.");
> +    return true;
> +  }
> +  return false;
> +}
> +
>  bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
>    if (skipOptnoneFunction(L))
>      return false;
> @@ -202,12 +268,49 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPa
>      TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock);
>    }
>
> -  bool Runtime = UserRuntime ? CurrentRuntime : UP.Runtime;
> +  // User-specified count (either as a command-line option or
> +  // constructor parameter) has highest precedence.
> +  unsigned Count = UserCount ? CurrentCount : 0;
> +
> +  // If there is no user-specified count, unroll pragmas have the next
> +  // highest precendence.
> +  if (Count == 0) {
> +    if (HasUnrollDisablePragma(L)) {
> +      // Loop has unroll(disable) pragma.
> +      return false;
> +    }
>
> -  // Use a default unroll-count if the user doesn't specify a value
> -  // and the trip count is a run-time value.  The default is different
> -  // for run-time or compile-time trip count loops.
> -  unsigned Count = UserCount ? CurrentCount : UP.Count;
> +    int PragmaCount;
> +    if (HasUnrollCountPragma(L, PragmaCount)) {
> +      if (PragmaCount == 1) {
> +        // Nothing to do.
> +        return false;
> +      }
> +      Count = PragmaCount;
> +      Threshold = NoThreshold;
> +    } else if (HasUnrollEnablePragma(L)) {
> +      // Loop has unroll(enable) pragma without a unroll_count pragma,
> +      // so unroll loop fully if possible.
> +      if (TripCount == 0) {
> +        DEBUG(dbgs() << "  Loop has unroll(enable) pragma but loop cannot be "
> +                        "fully unrolled because trip count is unknown.\n");
> +        // Continue with standard heuristic unrolling.
> +      } else if (TripCount > PragmaFullUnrollCountLimit) {
> +        DEBUG(dbgs() << "  Loop has unroll(enable) pragma but loop cannot be "
> +                        "fully unrolled because loop count is greater than "
> +                     << PragmaFullUnrollCountLimit);
> +        // Continue with standard heuristic unrolling.
> +      } else {
> +        Count = TripCount;
> +        Threshold = NoThreshold;
> +      }
> +    }
> +  }
> +
> +  if (Count == 0)
> +    Count = UP.Count;
> +
> +  bool Runtime = UserRuntime ? CurrentRuntime : UP.Runtime;
>    if (Runtime && Count == 0 && TripCount == 0)
>      Count = UnrollRuntimeCount;
>
>
> Added: llvm/trunk/test/Transforms/LoopUnroll/unroll-pragmas.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/unroll-pragmas.ll?rev=210721&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopUnroll/unroll-pragmas.ll (added)
> +++ llvm/trunk/test/Transforms/LoopUnroll/unroll-pragmas.ll Wed Jun 11 18:15:35 2014
> @@ -0,0 +1,285 @@
> +; RUN: opt < %s -loop-unroll -S | FileCheck %s
> +
> +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
> +target triple = "x86_64-unknown-linux-gnu"
> +
> +; loop4 contains a small loop which should be completely unrolled by
> +; the default unrolling heuristics.  It serves as a control for the
> +; unroll(disable) pragma test loop4_with_disable.
> +;
> +; CHECK-LABEL: @loop4(
> +; CHECK-NOT: br i1
> +define void @loop4(i32* nocapture %a) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 4
> +  br i1 %exitcond, label %for.end, label %for.body
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +
> +; #pragma clang loop unroll(disable)
> +;
> +; CHECK-LABEL: @loop4_with_disable(
> +; CHECK: store i32
> +; CHECK-NOT: store i32
> +; CHECK: br i1
> +define void @loop4_with_disable(i32* nocapture %a) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 4
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !1
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +!1 = metadata !{metadata !1, metadata !2}
> +!2 = metadata !{metadata !"llvm.loopunroll.enable", i1 false}
> +
> +; loop64 has a high enough count that it should *not* be unrolled by
> +; the default unrolling heuristic.  It serves as the control for the
> +; unroll(enable) pragma test loop64_with_.* tests below.
> +;
> +; CHECK-LABEL: @loop64(
> +; CHECK: store i32
> +; CHECK-NOT: store i32
> +; CHECK: br i1
> +define void @loop64(i32* nocapture %a) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 64
> +  br i1 %exitcond, label %for.end, label %for.body
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +
> +; #pragma clang loop unroll(enable)
> +; Loop should be fully unrolled.
> +;
> +; CHECK-LABEL: @loop64_with_enable(
> +; CHECK-NOT: br i1
> +define void @loop64_with_enable(i32* nocapture %a) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 64
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !3
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +!3 = metadata !{metadata !3, metadata !4}
> +!4 = metadata !{metadata !"llvm.loopunroll.enable", i1 true}
> +
> +; #pragma clang loop unroll_count(4)
> +; Loop should be unrolled 4 times.
> +;
> +; CHECK-LABEL: @loop64_with_count4(
> +; CHECK: store i32
> +; CHECK: store i32
> +; CHECK: store i32
> +; CHECK: store i32
> +; CHECK-NOT: store i32
> +; CHECK: br i1
> +define void @loop64_with_count4(i32* nocapture %a) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 64
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !5
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +!5 = metadata !{metadata !5, metadata !6}
> +!6 = metadata !{metadata !"llvm.loopunroll.count", i32 4}
> +
> +
> +; #pragma clang loop unroll_count(enable) unroll_count(4)
> +; Loop should be unrolled 4 times.
> +;
> +; CHECK-LABEL: @loop64_with_enable_and_count4(
> +; CHECK: store i32
> +; CHECK: store i32
> +; CHECK: store i32
> +; CHECK: store i32
> +; CHECK-NOT: store i32
> +; CHECK: br i1
> +define void @loop64_with_enable_and_count4(i32* nocapture %a) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 64
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !7
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +!7 = metadata !{metadata !7, metadata !6, metadata !4}
> +
> +; #pragma clang loop unroll_count(enable)
> +; Full unrolling is requested, but loop has a dynamic trip count so
> +; no unrolling should occur.
> +;
> +; CHECK-LABEL: @dynamic_loop_with_enable(
> +; CHECK: store i32
> +; CHECK-NOT: store i32
> +; CHECK: br i1
> +define void @dynamic_loop_with_enable(i32* nocapture %a, i32 %b) {
> +entry:
> +  %cmp3 = icmp sgt i32 %b, 0
> +  br i1 %cmp3, label %for.body, label %for.end, !llvm.loop !8
> +
> +for.body:                                         ; preds = %entry, %for.body
> +  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
> +  %exitcond = icmp eq i32 %lftr.wideiv, %b
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !8
> +
> +for.end:                                          ; preds = %for.body, %entry
> +  ret void
> +}
> +!8 = metadata !{metadata !8, metadata !4}
> +
> +; #pragma clang loop unroll_count(4)
> +; Loop has a dynamic trip count.  Unrolling should occur, but no
> +; conditional branches can be removed.
> +;
> +; CHECK-LABEL: @dynamic_loop_with_count4(
> +; CHECK-NOT: store
> +; CHECK: br i1
> +; CHECK: store
> +; CHECK: br i1
> +; CHECK: store
> +; CHECK: br i1
> +; CHECK: store
> +; CHECK: br i1
> +; CHECK: store
> +; CHECK: br i1
> +; CHECK-NOT: br i1
> +define void @dynamic_loop_with_count4(i32* nocapture %a, i32 %b) {
> +entry:
> +  %cmp3 = icmp sgt i32 %b, 0
> +  br i1 %cmp3, label %for.body, label %for.end, !llvm.loop !9
> +
> +for.body:                                         ; preds = %entry, %for.body
> +  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
> +  %exitcond = icmp eq i32 %lftr.wideiv, %b
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !9
> +
> +for.end:                                          ; preds = %for.body, %entry
> +  ret void
> +}
> +!9 = metadata !{metadata !9, metadata !6}
> +
> +; #pragma clang loop unroll_count(1)
> +; Loop should not be unrolled
> +;
> +; CHECK-LABEL: @unroll_1(
> +; CHECK: store i32
> +; CHECK-NOT: store i32
> +; CHECK: br i1
> +define void @unroll_1(i32* nocapture %a, i32 %b) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 4
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !10
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +!10 = metadata !{metadata !10, metadata !11}
> +!11 = metadata !{metadata !"llvm.loopunroll.count", i32 1}
> +
> +; #pragma clang loop unroll(enable)
> +; Loop has very high loop count (1 million) and full unrolling was requested.
> +; Loop should not be unrolled.
> +;
> +; CHECK-LABEL: @unroll_1M(
> +; CHECK: store i32
> +; CHECK-NOT: store i32
> +; CHECK: br i1
> +define void @unroll_1M(i32* nocapture %a, i32 %b) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %for.body, %entry
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
> +  %0 = load i32* %arrayidx, align 4
> +  %inc = add nsw i32 %0, 1
> +  store i32 %inc, i32* %arrayidx, align 4
> +  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> +  %exitcond = icmp eq i64 %indvars.iv.next, 1000000
> +  br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !12
> +
> +for.end:                                          ; preds = %for.body
> +  ret void
> +}
> +!12 = metadata !{metadata !12, metadata !4}
>
>
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