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LoopVectorize: PHIs with only outside users should prevent vectorization

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We check that instructions in the loop don't have outside users (except if
they are reduction values). Unfortunately, we skipped this check for
if-convertable PHIs.

Fixes PR16184.

llvm-svn: 183035
This commit is contained in:
Arnold Schwaighofer 2013-05-31 19:53:50 +00:00
parent c60747c08c
commit 12f1ab46d1
2 changed files with 71 additions and 13 deletions
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43
lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -2637,6 +2637,26 @@ static Type* getWiderType(DataLayout &DL, Type *Ty0, Type *Ty1) {
return Ty1;
}
/// \brief Check that the instruction has outside loop users and is not an
/// identified reduction variable.
static bool hasOutsideLoopUser(const Loop *TheLoop, Instruction *Inst,
SmallPtrSet<Value *, 4> &Reductions) {
// Reduction instructions are allowed to have exit users. All other
// instructions must not have external users.
if (!Reductions.count(Inst))
//Check that all of the users of the loop are inside the BB.
for (Value::use_iterator I = Inst->use_begin(), E = Inst->use_end();
I != E; ++I) {
Instruction *U = cast<Instruction>(*I);
// This user may be a reduction exit value.
if (!TheLoop->contains(U)) {
DEBUG(dbgs() << "LV: Found an outside user for : "<< *U << "\n");
return true;
}
}
return false;
}
bool LoopVectorizationLegality::canVectorizeInstrs() {
BasicBlock *PreHeader = TheLoop->getLoopPreheader();
BasicBlock *Header = TheLoop->getHeader();
@ -2669,8 +2689,13 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
// If this PHINode is not in the header block, then we know that we
// can convert it to select during if-conversion. No need to check if
// the PHIs in this block are induction or reduction variables.
if (*bb != Header)
continue;
if (*bb != Header) {
// Check that this instruction has no outside users or is an
// identified reduction value with an outside user.
if(!hasOutsideLoopUser(TheLoop, it, AllowedExit))
continue;
return false;
}
// We only allow if-converted PHIs with more than two incoming values.
if (Phi->getNumIncomingValues() != 2) {
@ -2769,17 +2794,9 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
// Reduction instructions are allowed to have exit users.
// All other instructions must not have external users.
if (!AllowedExit.count(it))
//Check that all of the users of the loop are inside the BB.
for (Value::use_iterator I = it->use_begin(), E = it->use_end();
I != E; ++I) {
Instruction *U = cast<Instruction>(*I);
// This user may be a reduction exit value.
if (!TheLoop->contains(U)) {
DEBUG(dbgs() << "LV: Found an outside user for : "<< *U << "\n");
return false;
}
}
if (hasOutsideLoopUser(TheLoop, it, AllowedExit))
return false;
} // next instr.
}

41
test/Transforms/LoopVectorize/no_outside_user.ll Normal file
View File

@ -0,0 +1,41 @@
; RUN: opt -S -loop-vectorize -force-vector-unroll=1 -force-vector-width=2 < %s | FileCheck %s
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32-S128"
@f = common global i32 0, align 4
@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
@c = common global i32 0, align 4
@a = common global i32 0, align 4
@b = common global i32 0, align 4
@e = common global i32 0, align 4
; We used to vectorize this loop. But it has a value that is used outside of the
; and is not a recognized reduction variable "tmp17".
; CHECK-NOT: <2 x i32>
define i32 @main() {
bb:
%b.promoted = load i32* @b, align 4
br label %.lr.ph.i
.lr.ph.i:
%tmp8 = phi i32 [ %tmp18, %bb16 ], [ %b.promoted, %bb ]
%tmp2 = icmp sgt i32 %tmp8, 10
br i1 %tmp2, label %bb16, label %bb10
bb10:
br label %bb16
bb16:
%tmp17 = phi i32 [ 0, %bb10 ], [ 1, %.lr.ph.i ]
%tmp18 = add nsw i32 %tmp8, 1
%tmp19 = icmp slt i32 %tmp18, 4
br i1 %tmp19, label %.lr.ph.i, label %f1.exit.loopexit
f1.exit.loopexit:
%.lcssa = phi i32 [ %tmp17, %bb16 ]
ret i32 %.lcssa
}