[LV] Relax Small Size Reduction Type Requirement

This patch enables small size reductions in which the source types are smaller
than the reduction type (e.g., computing an i16 sum from the values in an i8
array). The previous behavior was to only allow small size reductions if the
source types and reduction type were the same. The change accounts for the fact
that the existing sign- and zero-extend instructions in these cases should
still be included in the cost model.

Differential Revision: http://reviews.llvm.org/D12770

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247337 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/LoopUtils.cpp b/lib/Transforms/Utils/LoopUtils.cpp
index 785e2d4917ffac70d412cb1e511bcc9deffaa514..a8d20c65c1545362853911f456fc3e8e8c8c9ae2 100644 (file)
--- a/lib/Transforms/Utils/LoopUtils.cpp
+++ b/lib/Transforms/Utils/LoopUtils.cpp
@@ -98,6 +98,7 @@ bool RecurrenceDescriptor::getSourceExtensionKind(
 
   SmallVector<Instruction *, 8> Worklist;
   bool FoundOneOperand = false;
+  unsigned DstSize = RT->getPrimitiveSizeInBits();
   Worklist.push_back(Exit);
 
   // Traverse the instructions in the reduction expression, beginning with the
@@ -120,11 +121,16 @@ bool RecurrenceDescriptor::getSourceExtensionKind(
 
       // If the operand is not in Visited, it is not a reduction operation, but
       // it does feed into one. Make sure it is either a single-use sign- or
-      // zero-extend of the recurrence type.
+      // zero-extend instruction.
       CastInst *Cast = dyn_cast<CastInst>(J);
       bool IsSExtInst = isa<SExtInst>(J);
-      if (!Cast || !Cast->hasOneUse() || Cast->getSrcTy() != RT ||
-          !(isa<ZExtInst>(J) || IsSExtInst))
+      if (!Cast || !Cast->hasOneUse() || !(isa<ZExtInst>(J) || IsSExtInst))
+        return false;
+
+      // Ensure the source type of the extend is no larger than the reduction
+      // type. It is not necessary for the types to be identical.
+      unsigned SrcSize = Cast->getSrcTy()->getPrimitiveSizeInBits();
+      if (SrcSize > DstSize)
         return false;
 
       // Furthermore, ensure that all such extends are of the same kind.
@@ -136,9 +142,11 @@ bool RecurrenceDescriptor::getSourceExtensionKind(
         IsSigned = IsSExtInst;
       }
 
-      // Lastly, add the sign- or zero-extend to CI so that we can avoid
-      // accounting for it in the cost model.
-      CI.insert(Cast);
+      // Lastly, if the source type of the extend matches the reduction type,
+      // add the extend to CI so that we can avoid accounting for it in the
+      // cost model.
+      if (SrcSize == DstSize)
+        CI.insert(Cast);
     }
   }
   return true;

diff --git a/test/Transforms/LoopVectorize/AArch64/reduction-small-size.ll b/test/Transforms/LoopVectorize/AArch64/reduction-small-size.ll
index fdb21a94913f74b7dfcc6225b76d47c198875583..be08a63b212c035e0844d7eeed76d5886749f297 100644 (file)
--- a/test/Transforms/LoopVectorize/AArch64/reduction-small-size.ll
+++ b/test/Transforms/LoopVectorize/AArch64/reduction-small-size.ll
@@ -66,9 +66,9 @@ for.body:
   br i1 %exitcond, label %for.cond.for.cond.cleanup_crit_edge, label %for.body
 }
 
-; CHECK-LABEL: @reduction_i16
+; CHECK-LABEL: @reduction_i16_1
 ;
-; short reduction_i16(short *a, short *b, int n) {
+; short reduction_i16_1(short *a, short *b, int n) {
 ;   short sum = 0;
 ;   for (int i = 0; i < n; ++i)
 ;     sum += (a[i] + b[i]);
@@ -92,7 +92,7 @@ for.body:
 ; CHECK:   [[Rdx:%[a-zA-Z0-9.]+]] = extractelement <8 x i16>
 ; CHECK:   zext i16 [[Rdx]] to i32
 ;
-define i16 @reduction_i16(i16* nocapture readonly %a, i16* nocapture readonly %b, i32 %n) {
+define i16 @reduction_i16_1(i16* nocapture readonly %a, i16* nocapture readonly %b, i32 %n) {
 entry:
   %cmp.16 = icmp sgt i32 %n, 0
   br i1 %cmp.16, label %for.body.preheader, label %for.cond.cleanup
@@ -126,3 +126,66 @@ for.body:
   %exitcond = icmp eq i32 %lftr.wideiv, %n
   br i1 %exitcond, label %for.cond.for.cond.cleanup_crit_edge, label %for.body
 }
+
+; CHECK-LABEL: @reduction_i16_2
+;
+; short reduction_i16_2(char *a, char *b, int n) {
+;   short sum = 0;
+;   for (int i = 0; i < n; ++i)
+;     sum += (a[i] + b[i]);
+;   return sum;
+; }
+;
+; CHECK: vector.body:
+; CHECK:   phi <8 x i16>
+; CHECK:   [[Ld1:%[a-zA-Z0-9.]+]] = load <8 x i8>
+; CHECK:   zext <8 x i8> [[Ld1]] to <8 x i16>
+; CHECK:   [[Ld2:%[a-zA-Z0-9.]+]] = load <8 x i8>
+; CHECK:   zext <8 x i8> [[Ld2]] to <8 x i16>
+; CHECK:   add <8 x i16>
+; CHECK:   add <8 x i16>
+;
+; CHECK: middle.block:
+; CHECK:   shufflevector <8 x i16>
+; CHECK:   add <8 x i16>
+; CHECK:   shufflevector <8 x i16>
+; CHECK:   add <8 x i16>
+; CHECK:   shufflevector <8 x i16>
+; CHECK:   add <8 x i16>
+; CHECK:   [[Rdx:%[a-zA-Z0-9.]+]] = extractelement <8 x i16>
+; CHECK:   zext i16 [[Rdx]] to i32
+;
+define i16 @reduction_i16_2(i8* nocapture readonly %a, i8* nocapture readonly %b, i32 %n) {
+entry:
+  %cmp.14 = icmp sgt i32 %n, 0
+  br i1 %cmp.14, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:
+  br label %for.body
+
+for.cond.for.cond.cleanup_crit_edge:
+  %add5.lcssa = phi i32 [ %add5, %for.body ]
+  %conv6 = trunc i32 %add5.lcssa to i16
+  br label %for.cond.cleanup
+
+for.cond.cleanup:
+  %sum.0.lcssa = phi i16 [ %conv6, %for.cond.for.cond.cleanup_crit_edge ], [ 0, %entry ]
+  ret i16 %sum.0.lcssa
+
+for.body:
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %for.body.preheader ]
+  %sum.015 = phi i32 [ %add5, %for.body ], [ 0, %for.body.preheader ]
+  %arrayidx = getelementptr inbounds i8, i8* %a, i64 %indvars.iv
+  %0 = load i8, i8* %arrayidx, align 1
+  %conv = zext i8 %0 to i32
+  %arrayidx2 = getelementptr inbounds i8, i8* %b, i64 %indvars.iv
+  %1 = load i8, i8* %arrayidx2, align 1
+  %conv3 = zext i8 %1 to i32
+  %conv4.13 = and i32 %sum.015, 65535
+  %add = add nuw nsw i32 %conv, %conv4.13
+  %add5 = add nuw nsw i32 %add, %conv3
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.cond.for.cond.cleanup_crit_edge, label %for.body
+}