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Teach IRCE to look at branch weights when recognizing range checks

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Splitting a loop to make range checks redundant is profitable only if
the range check "never" fails. Make this fact a part of recognizing a
range check -- a branch is a range check only if it is expected to
pass (via branch_weights metadata).

Differential Revision: http://reviews.llvm.org/D7192

llvm-svn: 227249
This commit is contained in:
Sanjoy Das 2015-01-27 21:38:12 +00:00
parent fbc56e7e06
commit a8dd5128cf
6 changed files with 72 additions and 17 deletions
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17
lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
View File

@ -43,6 +43,7 @@
#include "llvm/ADT/Optional.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
@ -169,7 +170,8 @@ public:
/// Create an inductive range check out of BI if possible, else return
/// nullptr.
static InductiveRangeCheck *create(AllocatorTy &Alloc, BranchInst *BI,
Loop *L, ScalarEvolution &SE);
Loop *L, ScalarEvolution &SE,
BranchProbabilityInfo &BPI);
};
class InductiveRangeCheckElimination : public LoopPass {
@ -187,6 +189,7 @@ public:
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addRequired<ScalarEvolution>();
AU.addRequired<BranchProbabilityInfo>();
}
bool runOnLoop(Loop *L, LPPassManager &LPM) override;
@ -354,13 +357,20 @@ static bool SplitRangeCheckCondition(Loop *L, ScalarEvolution &SE,
return true;
}
InductiveRangeCheck *
InductiveRangeCheck::create(InductiveRangeCheck::AllocatorTy &A, BranchInst *BI,
Loop *L, ScalarEvolution &SE) {
Loop *L, ScalarEvolution &SE,
BranchProbabilityInfo &BPI) {
if (BI->isUnconditional() || BI->getParent() == L->getLoopLatch())
return nullptr;
BranchProbability LikelyTaken(15, 16);
if (BPI.getEdgeProbability(BI->getParent(), (unsigned) 0) < LikelyTaken)
return nullptr;
Value *Length = nullptr;
const SCEV *IndexSCEV = nullptr;
@ -1175,11 +1185,12 @@ bool InductiveRangeCheckElimination::runOnLoop(Loop *L, LPPassManager &LPM) {
InductiveRangeCheck::AllocatorTy IRCAlloc;
SmallVector<InductiveRangeCheck *, 16> RangeChecks;
ScalarEvolution &SE = getAnalysis<ScalarEvolution>();
BranchProbabilityInfo &BPI = getAnalysis<BranchProbabilityInfo>();
for (auto BBI : L->getBlocks())
if (BranchInst *TBI = dyn_cast<BranchInst>(BBI->getTerminator()))
if (InductiveRangeCheck *IRC =
InductiveRangeCheck::create(IRCAlloc, TBI, L, SE))
InductiveRangeCheck::create(IRCAlloc, TBI, L, SE, BPI))
RangeChecks.push_back(IRC);
if (RangeChecks.empty())

5
test/Transforms/IRCE/multiple-access-no-preloop.ll
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@ -13,13 +13,13 @@ define void @multiple_access_no_preloop(
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds.b ]
%idx.next = add i32 %idx, 1
%abc.a = icmp slt i32 %idx, %len.a
br i1 %abc.a, label %in.bounds.a, label %out.of.bounds
br i1 %abc.a, label %in.bounds.a, label %out.of.bounds, !prof !1
in.bounds.a:
%addr.a = getelementptr i32* %arr_a, i32 %idx
store i32 0, i32* %addr.a
%abc.b = icmp slt i32 %idx, %len.b
br i1 %abc.b, label %in.bounds.b, label %out.of.bounds
br i1 %abc.b, label %in.bounds.b, label %out.of.bounds, !prof !1
in.bounds.b:
%addr.b = getelementptr i32* %arr_b, i32 %idx
@ -57,3 +57,4 @@ define void @multiple_access_no_preloop(
; CHECK: br i1 %next.postloop, label %loop.postloop, label %exit.loopexit
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}

40
test/Transforms/IRCE/not-likely-taken.ll Normal file
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@ -0,0 +1,40 @@
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce < %s 2>&1 | FileCheck %s
; CHECK-NOT: constrained Loop
define void @multiple_access_no_preloop(
i32* %arr_a, i32* %a_len_ptr, i32* %arr_b, i32* %b_len_ptr, i32 %n) {
entry:
%len.a = load i32* %a_len_ptr, !range !0
%len.b = load i32* %b_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
br i1 %first.itr.check, label %loop, label %exit
loop:
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds.b ]
%idx.next = add i32 %idx, 1
%abc.a = icmp slt i32 %idx, %len.a
br i1 %abc.a, label %in.bounds.a, label %out.of.bounds, !prof !1
in.bounds.a:
%addr.a = getelementptr i32* %arr_a, i32 %idx
store i32 0, i32* %addr.a
%abc.b = icmp slt i32 %idx, %len.b
br i1 %abc.b, label %in.bounds.b, label %out.of.bounds, !prof !1
in.bounds.b:
%addr.b = getelementptr i32* %arr_b, i32 %idx
store i32 -1, i32* %addr.b
%next = icmp slt i32 %idx.next, %n
br i1 %next, label %loop, label %exit
out.of.bounds:
ret void
exit:
ret void
}
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 1, i32 1}

5
test/Transforms/IRCE/single-access-no-preloop.ll
View File

@ -10,7 +10,7 @@ define void @single_access_no_preloop_no_offset(i32 *%arr, i32 *%a_len_ptr, i32
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%abc = icmp slt i32 %idx, %len
br i1 %abc, label %in.bounds, label %out.of.bounds
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32* %arr, i32 %idx
@ -65,7 +65,7 @@ define void @single_access_no_preloop_with_offset(i32 *%arr, i32 *%a_len_ptr, i3
%idx.next = add i32 %idx, 1
%idx.for.abc = add i32 %idx, 4
%abc = icmp slt i32 %idx.for.abc, %len
br i1 %abc, label %in.bounds, label %out.of.bounds
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32* %arr, i32 %idx.for.abc
@ -108,3 +108,4 @@ define void @single_access_no_preloop_with_offset(i32 *%arr, i32 *%a_len_ptr, i3
; CHECK: br i1 %next.postloop, label %loop.postloop, label %exit.loopexit
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}

3
test/Transforms/IRCE/single-access-with-preloop.ll
View File

@ -13,7 +13,7 @@ define void @single_access_with_preloop(i32 *%arr, i32 *%a_len_ptr, i32 %n, i32
%abc.high = icmp slt i32 %array.idx, %len
%abc.low = icmp sge i32 %array.idx, 0
%abc = and i1 %abc.low, %abc.high
br i1 %abc, label %in.bounds, label %out.of.bounds
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32* %arr, i32 %array.idx
@ -57,3 +57,4 @@ define void @single_access_with_preloop(i32 *%arr, i32 *%a_len_ptr, i32 %n, i32
; CHECK: br i1 %next.postloop, label %loop.postloop, label %exit.loopexit
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}

19
test/Transforms/IRCE/with-parent-loops.ll
View File

@ -16,7 +16,7 @@ loop: ; preds = %in.bounds, %entry
%idx = phi i32 [ 0, %entry ], [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%abc = icmp slt i32 %idx, %len
br i1 %abc, label %in.bounds, label %out.of.bounds
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds: ; preds = %loop
%addr = getelementptr i32* %arr, i32 %idx
@ -50,7 +50,7 @@ loop.i: ; preds = %in.bounds.i, %loop
%idx.i = phi i32 [ 0, %loop ], [ %idx.next.i, %in.bounds.i ]
%idx.next.i = add i32 %idx.i, 1
%abc.i = icmp slt i32 %idx.i, %len.i
br i1 %abc.i, label %in.bounds.i, label %out.of.bounds.i
br i1 %abc.i, label %in.bounds.i, label %out.of.bounds.i, !prof !1
in.bounds.i: ; preds = %loop.i
%addr.i = getelementptr i32* %arr, i32 %idx.i
@ -96,7 +96,7 @@ loop.i.i: ; preds = %in.bounds.i.i, %loo
%idx.i.i = phi i32 [ 0, %loop.i ], [ %idx.next.i.i, %in.bounds.i.i ]
%idx.next.i.i = add i32 %idx.i.i, 1
%abc.i.i = icmp slt i32 %idx.i.i, %len.i.i
br i1 %abc.i.i, label %in.bounds.i.i, label %out.of.bounds.i.i
br i1 %abc.i.i, label %in.bounds.i.i, label %out.of.bounds.i.i, !prof !1
in.bounds.i.i: ; preds = %loop.i.i
%addr.i.i = getelementptr i32* %arr, i32 %idx.i.i
@ -140,7 +140,7 @@ loop.i: ; preds = %in.bounds.i, %loop
%idx.i = phi i32 [ 0, %loop ], [ %idx.next.i, %in.bounds.i ]
%idx.next.i = add i32 %idx.i, 1
%abc.i = icmp slt i32 %idx.i, %len.i
br i1 %abc.i, label %in.bounds.i, label %out.of.bounds.i
br i1 %abc.i, label %in.bounds.i, label %out.of.bounds.i, !prof !1
in.bounds.i: ; preds = %loop.i
%addr.i = getelementptr i32* %arr, i32 %idx.i
@ -163,7 +163,7 @@ loop.i6: ; preds = %in.bounds.i9, %inne
%idx.i3 = phi i32 [ 0, %inner_loop.exit ], [ %idx.next.i4, %in.bounds.i9 ]
%idx.next.i4 = add i32 %idx.i3, 1
%abc.i5 = icmp slt i32 %idx.i3, %len.i1
br i1 %abc.i5, label %in.bounds.i9, label %out.of.bounds.i10
br i1 %abc.i5, label %in.bounds.i9, label %out.of.bounds.i10, !prof !1
in.bounds.i9: ; preds = %loop.i6
%addr.i7 = getelementptr i32* %arr, i32 %idx.i3
@ -210,7 +210,7 @@ loop.i.i: ; preds = %in.bounds.i.i, %loo
%idx.i.i = phi i32 [ 0, %loop.i ], [ %idx.next.i.i, %in.bounds.i.i ]
%idx.next.i.i = add i32 %idx.i.i, 1
%abc.i.i = icmp slt i32 %idx.i.i, %len.i.i
br i1 %abc.i.i, label %in.bounds.i.i, label %out.of.bounds.i.i
br i1 %abc.i.i, label %in.bounds.i.i, label %out.of.bounds.i.i, !prof !1
in.bounds.i.i: ; preds = %loop.i.i
%addr.i.i = getelementptr i32* %arr, i32 %idx.i.i
@ -242,7 +242,7 @@ loop.i.i10: ; preds = %in.bounds.i.i13, %l
%idx.i.i7 = phi i32 [ 0, %loop.i6 ], [ %idx.next.i.i8, %in.bounds.i.i13 ]
%idx.next.i.i8 = add i32 %idx.i.i7, 1
%abc.i.i9 = icmp slt i32 %idx.i.i7, %len.i.i4
br i1 %abc.i.i9, label %in.bounds.i.i13, label %out.of.bounds.i.i14
br i1 %abc.i.i9, label %in.bounds.i.i13, label %out.of.bounds.i.i14, !prof !1
in.bounds.i.i13: ; preds = %loop.i.i10
%addr.i.i11 = getelementptr i32* %arr, i32 %idx.i.i7
@ -286,7 +286,7 @@ loop.i: ; preds = %in.bounds.i, %loop
%idx.i = phi i32 [ 0, %loop ], [ %idx.next.i, %in.bounds.i ]
%idx.next.i = add i32 %idx.i, 1
%abc.i = icmp slt i32 %idx.i, %len.i
br i1 %abc.i, label %in.bounds.i, label %out.of.bounds.i
br i1 %abc.i, label %in.bounds.i, label %out.of.bounds.i, !prof !1
in.bounds.i: ; preds = %loop.i
%addr.i = getelementptr i32* %arr, i32 %idx.i
@ -315,7 +315,7 @@ loop.i.i: ; preds = %in.bounds.i.i, %loo
%idx.i.i = phi i32 [ 0, %loop.i4 ], [ %idx.next.i.i, %in.bounds.i.i ]
%idx.next.i.i = add i32 %idx.i.i, 1
%abc.i.i = icmp slt i32 %idx.i.i, %len.i.i
br i1 %abc.i.i, label %in.bounds.i.i, label %out.of.bounds.i.i
br i1 %abc.i.i, label %in.bounds.i.i, label %out.of.bounds.i.i, !prof !1
in.bounds.i.i: ; preds = %loop.i.i
%addr.i.i = getelementptr i32* %arr, i32 %idx.i.i
@ -342,3 +342,4 @@ exit: ; preds = %with_parent.exit
attributes #0 = { alwaysinline }
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}