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The patch fixes PR27392.

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Summary:
 It is incorrect to compare TripCount (which is BECount + 1)
  with extraiters (or Count) to check if we should enter unrolled
  loop or not, because TripCount can potentially overflow
  (when BECount is max unsigned integer).
 While comparing BECount with (Count - 1) is overflow safe and
  therefore correct.

Reviewer: hfinkel

Differential Revision: http://reviews.llvm.org/D19256

From: Evgeny Stupachenko <evstupac@gmail.com>
llvm-svn: 267662
This commit is contained in:
Evgeny Stupachenko 2016-04-27 03:04:54 +00:00
parent 60e443db3d
commit 9d35c64dc2
5 changed files with 38 additions and 27 deletions
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19
lib/Transforms/Utils/LoopUnrollRuntime.cpp
View File

@ -246,7 +246,7 @@ static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
Instruction *InsertPt = NewExit->getTerminator();
IRBuilder<> B(InsertPt);
Value *BrLoopExit = B.CreateIsNotNull(ModVal);
Value *BrLoopExit = B.CreateIsNotNull(ModVal, "lcmp.mod");
assert(Exit && "Loop must have a single exit block only");
// Split the exit to maintain loop canonicalization guarantees
SmallVector<BasicBlock*, 4> Preds(predecessors(Exit));
@ -416,7 +416,7 @@ static void CloneLoopBlocks(Loop *L, Value *NewIter,
///
/// ***Epilog case***
/// extraiters = tripcount % loopfactor
/// if (extraiters == tripcount) jump LoopExit:
/// if (tripcount < loopfactor) jump LoopExit:
/// unroll_iters = tripcount - extraiters
/// Loop: LoopBody; (executes unroll_iter times);
/// unroll_iter -= 1
@ -575,14 +575,15 @@ bool llvm::UnrollRuntimeLoopRemainder(Loop *L, unsigned Count,
ConstantInt::get(BECount->getType(), Count),
"xtraiter");
}
Value *CmpOperand =
UseEpilogRemainder ? TripCount :
ConstantInt::get(TripCount->getType(), 0);
Value *BranchVal = B.CreateICmpNE(ModVal, CmpOperand, "lcmp.mod");
BasicBlock *FirstLoop = UseEpilogRemainder ? NewPreHeader : PrologPreHeader;
BasicBlock *SecondLoop = UseEpilogRemainder ? NewExit : PrologExit;
Value *BranchVal =
UseEpilogRemainder ? B.CreateICmpULT(BECount,
ConstantInt::get(BECount->getType(),
Count - 1)) :
B.CreateIsNotNull(ModVal, "lcmp.mod");
BasicBlock *RemainderLoop = UseEpilogRemainder ? NewExit : PrologPreHeader;
BasicBlock *UnrollingLoop = UseEpilogRemainder ? NewPreHeader : PrologExit;
// Branch to either remainder (extra iterations) loop or unrolling loop.
B.CreateCondBr(BranchVal, FirstLoop, SecondLoop);
B.CreateCondBr(BranchVal, RemainderLoop, UnrollingLoop);
PreHeaderBR->eraseFromParent();
Function *F = Header->getParent();
// Get an ordered list of blocks in the loop to help with the ordering of the

10
test/Transforms/LoopUnroll/AArch64/runtime-loop.ll
View File

@ -4,16 +4,14 @@
; Tests for unrolling loops with run-time trip counts
; EPILOG: %xtraiter = and i32 %n
; EPILOG: %lcmp.mod = icmp ne i32 %xtraiter, %n
; EPILOG: br i1 %lcmp.mod, label %for.body.preheader.new, label %for.end.loopexit.unr-lcssa
; EPILOG: for.body:
; EPILOG: %lcmp.mod = icmp ne i32 %xtraiter, 0
; EPILOG: br i1 %lcmp.mod, label %for.body.epil.preheader, label %for.end.loopexit
; EPILOG: for.body.epil:
; PROLOG: %xtraiter = and i32 %n
; PROLOG: %lcmp.mod = icmp ne i32 %xtraiter, 0
; PROLOG: br i1 %lcmp.mod, label %for.body.prol.preheader, label %for.body.prol.loopexit
; EPILOG: for.body:
; EPILOG: for.body.epil:
; PROLOG: for.body.prol:
; PROLOG: for.body:

4
test/Transforms/LoopUnroll/runtime-loop.ll
View File

@ -6,8 +6,8 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
; Tests for unrolling loops with run-time trip counts
; EPILOG: %xtraiter = and i32 %n
; EPILOG: %lcmp.mod = icmp ne i32 %xtraiter, %n
; EPILOG: br i1 %lcmp.mod, label %for.body.preheader.new, label %for.end.loopexit.unr-lcssa
; EPILOG: %lcmp.mod = icmp ne i32 %xtraiter, 0
; EPILOG: br i1 %lcmp.mod, label %for.body.epil.preheader, label %for.end.loopexit
; PROLOG: %xtraiter = and i32 %n
; PROLOG: %lcmp.mod = icmp ne i32 %xtraiter, 0

2
test/Transforms/LoopUnroll/runtime-loop1.ll
View File

@ -5,7 +5,7 @@
; EPILOG: for.body.preheader:
; EPILOG: br i1 %lcmp.mod, label %for.body.preheader.new, label %for.end.loopexit.unr-lcssa, !dbg [[PH_LOC:![0-9]+]]
; EPILOG: br i1 %1, label %for.end.loopexit.unr-lcssa, label %for.body.preheader.new, !dbg [[PH_LOC:![0-9]+]]
; EPILOG: for.body:
; EPILOG: br i1 %niter.ncmp.1, label %for.end.loopexit.unr-lcssa.loopexit, label %for.body, !dbg [[BODY_LOC:![0-9]+]]
; EPILOG-NOT: br i1 %niter.ncmp.2, label %for.end.loopexit{{.*}}, label %for.body

30
test/Transforms/LoopUnroll/tripcount-overflow.ll
View File

@ -1,4 +1,5 @@
; RUN: opt < %s -S -unroll-runtime -unroll-count=2 -loop-unroll | FileCheck %s
; RUN: opt < %s -S -unroll-runtime -unroll-count=2 -loop-unroll | FileCheck %s -check-prefix=EPILOG
; RUN: opt < %s -S -unroll-runtime -unroll-count=2 -loop-unroll -unroll-runtime-epilog=false | FileCheck %s -check-prefix=PROLOG
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
; This test case documents how runtime loop unrolling handles the case
@ -9,17 +10,28 @@ target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
; is divisible by 2. The prologue then branches to the unrolled loop
; and executes the 2^32 iterations there, in groups of 2.
; EPILOG: entry:
; CHECK: entry:
; CHECK-NEXT: %0 = add i32 %N, 1
; CHECK-NEXT: %xtraiter = and i32 %0, 1
; CHECK-NEXT: %lcmp.mod = icmp ne i32 %xtraiter, %0
; CHECK-NEXT: br i1 %lcmp.mod, label %entry.new, label %while.end.unr-lcssa
; EPILOG-NEXT: %0 = add i32 %N, 1
; EPILOG-NEXT: %xtraiter = and i32 %0, 1
; EPILOG-NEXT: %1 = icmp ult i32 %N, 1
; EPILOG-NEXT: br i1 %1, label %while.end.unr-lcssa, label %entry.new
; EPILOG: while.body:
; CHECK: while.body.epil:
; CHECK: br label %while.end.epilog-lcssa
; EPILOG: %lcmp.mod = icmp ne i32 %xtraiter, 0
; EPILOG-NEXT: br i1 %lcmp.mod, label %while.body.epil.preheader, label %while.end
; EPILOG: while.body.epil:
; CHECK: while.end.epilog-lcssa:
; PROLOG: entry:
; PROLOG-NEXT: %0 = add i32 %N, 1
; PROLOG-NEXT: %xtraiter = and i32 %0, 1
; PROLOG-NEXT: %lcmp.mod = icmp ne i32 %xtraiter, 0
; PROLOG-NEXT: br i1 %lcmp.mod, label %while.body.prol.preheader, label %while.body.prol.loopexit
; PROLOG: while.body.prol:
; PROLOG: %1 = icmp ult i32 %N, 1
; PROLOG-NEXT: br i1 %1, label %while.end, label %entry.new
; PROLOG: while.body:
; Function Attrs: nounwind readnone ssp uwtable
define i32 @foo(i32 %N) {