[llvm] r295056 - [SLP] Fix for PR31879: vectorize repeated scalar ops that don't get put

[Alexey Bataev via llvm-commits]

Author: abataev
Date: Tue Feb 14 09:20:48 2017
New Revision: 295056

URL: http://llvm.org/viewvc/llvm-project?rev=295056&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
    llvm/trunk/test/Transforms/SLPVectorizer/X86/extractelement.ll

Modified: llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp?rev=295056&r1=295055&r2=295056&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp Tue Feb 14 09:20:48 2017
@@ -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);

Modified: llvm/trunk/test/Transforms/SLPVectorizer/X86/extractelement.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SLPVectorizer/X86/extractelement.ll?rev=295056&r1=295055&r2=295056&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SLPVectorizer/X86/extractelement.ll (original)
+++ llvm/trunk/test/Transforms/SLPVectorizer/X86/extractelement.ll Tue Feb 14 09:20:48 2017
@@ -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 fl
 
 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