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[SLP] Fix for PR31879: vectorize repeated scalar ops that don't get put 

back into a vector

Previously the cost of the existing ExtractElement/ExtractValue
instructions was considered as a dead cost only if it was detected that
they have only one use. But these instructions may be considered
dead also if users of the instructions are also going to be vectorized,
like:
```
%x0 = extractelement <2 x float> %x, i32 0
%x1 = extractelement <2 x float> %x, i32 1
%x0x0 = fmul float %x0, %x0
%x1x1 = fmul float %x1, %x1
%add = fadd float %x0x0, %x1x1
```
This can be transformed to
```
%1 = fmul <2 x float> %x, %x
%2 = extractelement <2 x float> %1, i32 0
%3 = extractelement <2 x float> %1, i32 1
%add = fadd float %2, %3
```
because though `%x0` and `%x1` have 2 users each other, these users are
part of the vectorized tree and we can consider these `extractelement`
instructions as dead.

Differential Revision: https://reviews.llvm.org/D29900

llvm-svn: 295056
This commit is contained in:
Alexey Bataev 2017-02-14 15:20:48 +00:00
parent dc66a82dc7
commit 2a2f35d59c
2 changed files with 25 additions and 17 deletions
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8
llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
View File

@ -1660,7 +1660,13 @@ int BoUpSLP::getEntryCost(TreeEntry *E) {
int DeadCost = 0;
for (unsigned i = 0, e = VL.size(); i < e; ++i) {
Instruction *E = cast<Instruction>(VL[i]);
if (E->hasOneUse())
// If all users are going to be vectorized, instruction can be
// considered as dead.
// The same, if have only one user, it will be vectorized for sure.
if (E->hasOneUse() ||
std::all_of(E->user_begin(), E->user_end(), [this](User *U) {
return ScalarToTreeEntry.count(U) > 0;
}))
// Take credit for instruction that will become dead.
DeadCost +=
TTI->getVectorInstrCost(Instruction::ExtractElement, VecTy, i);

34
llvm/test/Transforms/SLPVectorizer/X86/extractelement.ll
View File

@ -7,11 +7,10 @@
define float @f(<2 x float> %x) {
; CHECK-LABEL: @f(
; CHECK-NEXT: [[X0:%.*]] = extractelement <2 x float> [[X:%.*]], i32 0
; CHECK-NEXT: [[X1:%.*]] = extractelement <2 x float> [[X]], i32 1
; CHECK-NEXT: [[X0X0:%.*]] = fmul float [[X0]], [[X0]]
; CHECK-NEXT: [[X1X1:%.*]] = fmul float [[X1]], [[X1]]
; CHECK-NEXT: [[ADD:%.*]] = fadd float [[X0X0]], [[X1X1]]
; CHECK-NEXT: [[TMP1:%.*]] = fmul <2 x float> [[X:%.*]], [[X]]
; CHECK-NEXT: [[TMP2:%.*]] = extractelement <2 x float> [[TMP1]], i32 0
; CHECK-NEXT: [[TMP3:%.*]] = extractelement <2 x float> [[TMP1]], i32 1
; CHECK-NEXT: [[ADD:%.*]] = fadd float [[TMP2]], [[TMP3]]
; CHECK-NEXT: ret float [[ADD]]
;
%x0 = extractelement <2 x float> %x, i32 0
@ -24,13 +23,13 @@ define float @f(<2 x float> %x) {
define float @f_used_out_of_tree(<2 x float> %x) {
; THRESH2-LABEL: @f_used_out_of_tree(
; THRESH2-NEXT: [[X0:%.*]] = extractelement <2 x float> [[X:%.*]], i32 0
; THRESH2-NEXT: [[X1:%.*]] = extractelement <2 x float> [[X]], i32 1
; THRESH2-NEXT: [[X0X0:%.*]] = fmul float [[X0]], [[X0]]
; THRESH2-NEXT: [[X1X1:%.*]] = fmul float [[X1]], [[X1]]
; THRESH2-NEXT: [[ADD:%.*]] = fadd float [[X0X0]], [[X1X1]]
; THRESH2-NEXT: [[TMP1:%.*]] = extractelement <2 x float> [[X:%.*]], i32 0
; THRESH2-NEXT: [[TMP2:%.*]] = fmul <2 x float> [[X]], [[X]]
; THRESH2-NEXT: [[TMP3:%.*]] = extractelement <2 x float> [[TMP2]], i32 0
; THRESH2-NEXT: [[TMP4:%.*]] = extractelement <2 x float> [[TMP2]], i32 1
; THRESH2-NEXT: [[ADD:%.*]] = fadd float [[TMP3]], [[TMP4]]
; THRESH2-NEXT: store float [[ADD]], float* @a
; THRESH2-NEXT: ret float [[X0]]
; THRESH2-NEXT: ret float [[TMP1]]
;
%x0 = extractelement <2 x float> %x, i32 0
%x1 = extractelement <2 x float> %x, i32 1
@ -43,12 +42,15 @@ define float @f_used_out_of_tree(<2 x float> %x) {
define float @f_used_twice_in_tree(<2 x float> %x) {
; THRESH1-LABEL: @f_used_twice_in_tree(
; THRESH1-NEXT: [[X0:%.*]] = extractelement <2 x float> [[X:%.*]], i32 0
; THRESH1-NEXT: [[X1:%.*]] = extractelement <2 x float> [[X]], i32 1
; THRESH1-NEXT: [[X0X0:%.*]] = fmul float [[X0]], [[X1]]
; THRESH1-NEXT: [[X1X1:%.*]] = fmul float [[X1]], [[X1]]
; THRESH1-NEXT: [[ADD:%.*]] = fadd float [[X0X0]], [[X1X1]]
; THRESH1-NEXT: [[TMP1:%.*]] = extractelement <2 x float> [[X:%.*]], i32 1
; THRESH1-NEXT: [[TMP2:%.*]] = insertelement <2 x float> undef, float [[TMP1]], i32 0
; THRESH1-NEXT: [[TMP3:%.*]] = insertelement <2 x float> [[TMP2]], float [[TMP1]], i32 1
; THRESH1-NEXT: [[TMP4:%.*]] = fmul <2 x float> [[X]], [[TMP3]]
; THRESH1-NEXT: [[TMP5:%.*]] = extractelement <2 x float> [[TMP4]], i32 0
; THRESH1-NEXT: [[TMP6:%.*]] = extractelement <2 x float> [[TMP4]], i32 1
; THRESH1-NEXT: [[ADD:%.*]] = fadd float [[TMP5]], [[TMP6]]
; THRESH1-NEXT: ret float [[ADD]]
;
%x0 = extractelement <2 x float> %x, i32 0
%x1 = extractelement <2 x float> %x, i32 1
%x0x0 = fmul float %x0, %x1