[PATCH] D46302: [LV] Fix for PR37248, Broadcast codegen incorrectly assumed vector loop body is single basic block

[Hideki Saito via Phabricator via llvm-commits]

hsaito updated this revision to Diff 145425.
hsaito added a comment.

SafeToHoist logic made straightforward. FileCheck added to lit test. The test passes after the fix.


https://reviews.llvm.org/D46302

Files:
  lib/Transforms/Vectorize/LoopVectorize.cpp
  test/Transforms/LoopVectorize/pr37248.ll


Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -1737,14 +1737,16 @@
 //===----------------------------------------------------------------------===//
 
 Value *InnerLoopVectorizer::getBroadcastInstrs(Value *V) {
-  // We need to place the broadcast of invariant variables outside the loop.
+  // We need to place the broadcast of invariant variables outside the loop,
+  // but only if it's proven safe to do so. Else, broadcast will be inside
+  // vector loop body.
   Instruction *Instr = dyn_cast<Instruction>(V);
-  bool NewInstr = (Instr && Instr->getParent() == LoopVectorBody);
-  bool Invariant = OrigLoop->isLoopInvariant(V) && !NewInstr;
-
+  bool SafeToHoist = OrigLoop->isLoopInvariant(V) &&
+                     (!Instr ||
+                      DT->dominates(Instr->getParent(), LoopVectorPreHeader));
   // Place the code for broadcasting invariant variables in the new preheader.
   IRBuilder<>::InsertPointGuard Guard(Builder);
-  if (Invariant)
+  if (SafeToHoist)
     Builder.SetInsertPoint(LoopVectorPreHeader->getTerminator());
 
   // Broadcast the scalar into all locations in the vector.
Index: test/Transforms/LoopVectorize/pr37248.ll
===================================================================
--- test/Transforms/LoopVectorize/pr37248.ll
+++ test/Transforms/LoopVectorize/pr37248.ll
@@ -0,0 +1,42 @@
+; RUN: opt -passes='loop-vectorize' -force-vector-width=2 -S < %s | FileCheck %s
+;
+; Forcing VF=2 to trigger vector code gen
+;
+; This is a test case that let's vectorizer's code gen to generate
+; more than one BasicBlocks in the loop body (emulated masked scatter)
+; for those targets that do not support masked scatter. Broadcast
+; code generation was previously dependent on loop body being
+; a single basic block and this test case exposed incorrect code gen
+; resulting in an assert in IL verification. Test passes if IL verification
+; does not fail.
+;
+; Performing minimal check in the output to ensure the loop is actually
+; vectorized.
+;
+; CHECK: vector.body
+
+ at a = external global [2 x i16], align 1
+
+define void @f1() {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %land.end, %entry
+  %0 = phi i32 [ undef, %entry ], [ %dec, %land.end ]
+  br i1 undef, label %land.end, label %land.rhs
+
+land.rhs:                                         ; preds = %for.body
+  %1 = load i32, i32* undef, align 1
+  br label %land.end
+
+land.end:                                         ; preds = %land.rhs, %for.body
+  %2 = trunc i32 %0 to i16
+  %arrayidx = getelementptr inbounds [2 x i16], [2 x i16]* @a, i16 0, i16 %2
+  store i16 undef, i16* %arrayidx, align 1
+  %dec = add nsw i32 %0, -1
+  %cmp = icmp sgt i32 %0, 1
+  br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge
+
+for.cond.for.end_crit_edge:                       ; preds = %land.end
+  unreachable
+}


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