[llvm] r345959 - [LV] Avoid vectorizing loops under opt for size that involve SCEV checks
Ayal Zaks via llvm-commits
llvm-commits at lists.llvm.org
Fri Nov 2 02:16:12 PDT 2018
Author: ayalz
Date: Fri Nov 2 02:16:12 2018
New Revision: 345959
URL: http://llvm.org/viewvc/llvm-project?rev=345959&view=rev
Log:
[LV] Avoid vectorizing loops under opt for size that involve SCEV checks
Fix PR39417, PR39497
The loop vectorizer may generate runtime SCEV checks for overflow and stride==1
cases, leading to execution of original scalar loop. The latter is forbidden
when optimizing for size. An assert introduced in r344743 triggered the above
PR's showing it does happen. This patch fixes this behavior by preventing
vectorization in such cases.
Differential Revision: https://reviews.llvm.org/D53612
Added:
llvm/trunk/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll
Modified:
llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
llvm/trunk/test/Transforms/LoopVectorize/X86/optsize.ll
Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=345959&r1=345958&r2=345959&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Fri Nov 2 02:16:12 2018
@@ -2557,7 +2557,8 @@ void InnerLoopVectorizer::emitSCEVChecks
if (C->isZero())
return;
- assert(!Cost->foldTailByMasking() && "Cannot check stride when folding tail");
+ assert(!Cost->foldTailByMasking() &&
+ "Cannot SCEV check stride or overflow when folding tail");
// Create a new block containing the stride check.
BB->setName("vector.scevcheck");
auto *NewBB = BB->splitBasicBlock(BB->getTerminator(), "vector.ph");
@@ -4637,6 +4638,29 @@ Optional<unsigned> LoopVectorizationCost
return None;
}
+ if (!PSE.getUnionPredicate().getPredicates().empty()) {
+ ORE->emit(createMissedAnalysis("CantVersionLoopWithOptForSize")
+ << "runtime SCEV checks needed. Enable vectorization of this "
+ "loop with '#pragma clang loop vectorize(enable)' when "
+ "compiling with -Os/-Oz");
+ LLVM_DEBUG(
+ dbgs()
+ << "LV: Aborting. Runtime SCEV check is required with -Os/-Oz.\n");
+ return None;
+ }
+
+ // FIXME: Avoid specializing for stride==1 instead of bailing out.
+ if (!Legal->getLAI()->getSymbolicStrides().empty()) {
+ ORE->emit(createMissedAnalysis("CantVersionLoopWithOptForSize")
+ << "runtime stride == 1 checks needed. Enable vectorization of "
+ "this loop with '#pragma clang loop vectorize(enable)' when "
+ "compiling with -Os/-Oz");
+ LLVM_DEBUG(
+ dbgs()
+ << "LV: Aborting. Runtime stride check is required with -Os/-Oz.\n");
+ return None;
+ }
+
// If we optimize the program for size, avoid creating the tail loop.
LLVM_DEBUG(dbgs() << "LV: Found trip count: " << TC << '\n');
Modified: llvm/trunk/test/Transforms/LoopVectorize/X86/optsize.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/X86/optsize.ll?rev=345959&r1=345958&r2=345959&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/X86/optsize.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/X86/optsize.ll Fri Nov 2 02:16:12 2018
@@ -3,6 +3,7 @@
; will produce a tail loop with the optimize for size or the minimize size
; attributes. This is a target-dependent version of the test.
; RUN: opt < %s -loop-vectorize -force-vector-width=64 -S -mtriple=x86_64-unknown-linux -mcpu=skx | FileCheck %s
+; RUN: opt < %s -loop-vectorize -S -mtriple=x86_64-unknown-linux -mcpu=skx | FileCheck %s --check-prefix AUTOVF
target datalayout = "E-m:e-p:32:32-i64:32-f64:32:64-a:0:32-n32-S128"
@@ -136,3 +137,62 @@ for.end:
attributes #1 = { minsize }
+
+; We can't vectorize this one because we version for stride==1; even having TC
+; a multiple of VF.
+; CHECK-LABEL: @scev4stride1
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: for.body:
+; AUTOVF-LABEL: @scev4stride1
+; AUTOVF-NOT: vector.scevcheck
+; AUTOVF-NOT: vector.body:
+; AUTOVF-LABEL: for.body:
+define void @scev4stride1(i32* noalias nocapture %a, i32* noalias nocapture readonly %b, i32 %k) #2 {
+for.body.preheader:
+ br label %for.body
+
+for.body: ; preds = %for.body.preheader, %for.body
+ %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+ %mul = mul nsw i32 %i.07, %k
+ %arrayidx = getelementptr inbounds i32, i32* %b, i32 %mul
+ %0 = load i32, i32* %arrayidx, align 4
+ %arrayidx1 = getelementptr inbounds i32, i32* %a, i32 %i.07
+ store i32 %0, i32* %arrayidx1, align 4
+ %inc = add nuw nsw i32 %i.07, 1
+ %exitcond = icmp eq i32 %inc, 256
+ br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit: ; preds = %for.body
+ ret void
+}
+
+attributes #2 = { optsize }
+
+
+; PR39497
+; We can't vectorize this one because we version for overflow check and tiny
+; trip count leads to opt-for-size (which otherwise could fold the tail by
+; masking).
+; CHECK-LABEL: @main
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: for.cond:
+; AUTOVF-LABEL: @main
+; AUTOVF-NOT: vector.scevcheck
+; AUTOVF-NOT: vector.body:
+; AUTOVF-LABEL: for.cond:
+define i32 @main() local_unnamed_addr {
+while.cond:
+ br label %for.cond
+
+for.cond:
+ %d.0 = phi i32 [ 0, %while.cond ], [ %add, %for.cond ]
+ %conv = and i32 %d.0, 65535
+ %cmp = icmp ult i32 %conv, 4
+ %add = add nuw nsw i32 %conv, 1
+ br i1 %cmp, label %for.cond, label %while.cond.loopexit
+
+while.cond.loopexit:
+ ret i32 0
+}
Added: llvm/trunk/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll?rev=345959&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll (added)
+++ llvm/trunk/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll Fri Nov 2 02:16:12 2018
@@ -0,0 +1,54 @@
+; RUN: opt -S -loop-vectorize -force-vector-width=4 -force-vector-interleave=1 < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; PR39417
+; Check that the need for overflow check prevents vectorizing a loop with tiny
+; trip count (which implies opt for size).
+; CHECK-LABEL: @func_34
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: bb67:
+define void @func_34() {
+bb1:
+ br label %bb67
+
+bb67:
+ %storemerge2 = phi i32 [ 0, %bb1 ], [ %_tmp2300, %bb67 ]
+ %sext = shl i32 %storemerge2, 16
+ %_tmp2299 = ashr exact i32 %sext, 16
+ %_tmp2300 = add nsw i32 %_tmp2299, 1
+ %_tmp2310 = trunc i32 %_tmp2300 to i16
+ %_tmp2312 = icmp slt i16 %_tmp2310, 3
+ br i1 %_tmp2312, label %bb67, label %bb68
+
+bb68:
+ ret void
+}
+
+; Check that the need for stride==1 check prevents vectorizing a loop under opt
+; for size.
+; CHECK-LABEL: @scev4stride1
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: for.body:
+define void @scev4stride1(i32* noalias nocapture %a, i32* noalias nocapture readonly %b, i32 %k) #0 {
+for.body.preheader:
+ br label %for.body
+
+for.body:
+ %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+ %mul = mul nsw i32 %i.07, %k
+ %arrayidx = getelementptr inbounds i32, i32* %b, i32 %mul
+ %0 = load i32, i32* %arrayidx, align 4
+ %arrayidx1 = getelementptr inbounds i32, i32* %a, i32 %i.07
+ store i32 %0, i32* %arrayidx1, align 4
+ %inc = add nuw nsw i32 %i.07, 1
+ %exitcond = icmp eq i32 %inc, 1024
+ br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:
+ ret void
+}
+
+attributes #0 = { optsize }
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