[LoopUtils, LV] Fix PR26734

The vectorization of first-order recurrences (r261346) caused PR26734. When
detecting these recurrences, we need to ensure that the previous value is
actually defined inside the loop. This patch includes the fix and test case.

llvm-svn: 262624

2 files changed, 50 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 42ba0124db1..1f84eca6059 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -543,7 +543,7 @@ bool RecurrenceDescriptor::isFirstOrderRecurrence(PHINode *Phi, Loop *TheLoop,
   // Get the previous value. The previous value comes from the latch edge while
   // the initial value comes form the preheader edge.
   auto *Previous = dyn_cast<Instruction>(Phi->getIncomingValueForBlock(Latch));
-  if (!Previous)
+  if (!Previous || !TheLoop->contains(Previous))
     return false;
 
   // Ensure every user of the phi node is dominated by the previous value. The
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/first-order-recurrence.ll b/llvm/test/Transforms/LoopVectorize/AArch64/first-order-recurrence.ll
index f556cd1319f..de950a84a1a 100644
--- a/llvm/test/Transforms/LoopVectorize/AArch64/first-order-recurrence.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/first-order-recurrence.ll
@@ -207,3 +207,52 @@ for.end.loopexit:
 for.end:
   ret void
 }
+
+; CHECK-LABEL: @PR26734
+;
+; void PR26734(short *a, int *b, int *c, int d, short *e) {
+;   for (; d != 21; d++) {
+;     *b &= *c;
+;     *e = *a - 6;
+;     *c = *e;
+;   }
+; }
+;
+; CHECK-NOT: vector.ph:
+;
+define void @PR26734(i16* %a, i32* %b, i32* %c, i32 %d, i16* %e) {
+entry:
+  %cmp4 = icmp eq i32 %d, 21
+  br i1 %cmp4, label %entry.for.end_crit_edge, label %for.body.lr.ph
+
+entry.for.end_crit_edge:
+  %.pre = load i32, i32* %b, align 4
+  br label %for.end
+
+for.body.lr.ph:
+  %0 = load i16, i16* %a, align 2
+  %sub = add i16 %0, -6
+  %conv2 = sext i16 %sub to i32
+  %c.promoted = load i32, i32* %c, align 4
+  %b.promoted = load i32, i32* %b, align 4
+  br label %for.body
+
+for.body:
+  %inc7 = phi i32 [ %d, %for.body.lr.ph ], [ %inc, %for.body ]
+  %and6 = phi i32 [ %b.promoted, %for.body.lr.ph ], [ %and, %for.body ]
+  %conv25 = phi i32 [ %c.promoted, %for.body.lr.ph ], [ %conv2, %for.body ]
+  %and = and i32 %and6, %conv25
+  %inc = add nsw i32 %inc7, 1
+  %cmp = icmp eq i32 %inc, 21
+  br i1 %cmp, label %for.cond.for.end_crit_edge, label %for.body
+
+for.cond.for.end_crit_edge:
+  %and.lcssa = phi i32 [ %and, %for.body ]
+  store i32 %conv2, i32* %c, align 4
+  store i32 %and.lcssa, i32* %b, align 4
+  store i16 %sub, i16* %e, align 2
+  br label %for.end
+
+for.end:
+  ret void
+}