[PATCH] D35227: [LV] Don't allow outside uses of IVs if the SCEV is predicated on loop conditions

[Michael Kuperstein via Phabricator via llvm-commits]

mkuper created this revision.
Herald added a subscriber: mzolotukhin.

This fixes PR33706.

I'm still not 100% sure the PSCEV actually makes sense here. Sanjoy, if you could take a look (even post-commit) at the original PR, that would be great.


https://reviews.llvm.org/D35227

Files:
  lib/Transforms/Vectorize/LoopVectorize.cpp
  test/Transforms/LoopVectorize/pr33706.ll


Index: test/Transforms/LoopVectorize/pr33706.ll
===================================================================
--- test/Transforms/LoopVectorize/pr33706.ll
+++ test/Transforms/LoopVectorize/pr33706.ll
@@ -0,0 +1,61 @@
+; RUN: opt -S -loop-vectorize -force-vector-interleave=1 -force-vector-width=2 < %s | FileCheck %s
+
+ at global = local_unnamed_addr global i32 0, align 4
+ at global.1 = local_unnamed_addr global i32 0, align 4
+ at global.2 = local_unnamed_addr global float 0x3EF0000000000000, align 4
+
+; CHECK-LABEL: @PR33706
+; CHECK-NOT: <2 x i32>
+define void @PR33706(float* nocapture readonly %arg, float* nocapture %arg1, i32 %arg2) local_unnamed_addr {
+bb:
+  %tmp = load i32, i32* @global.1, align 4
+  %tmp3 = getelementptr inbounds float, float* %arg, i64 190
+  %tmp4 = getelementptr inbounds float, float* %arg1, i64 512
+  %tmp5 = and i32 %tmp, 65535
+  %tmp6 = icmp ugt i32 %arg2, 65536
+  br i1 %tmp6, label %bb7, label %bb9
+
+bb7:                                              ; preds = %bb
+  %tmp8 = load i32, i32* @global, align 4
+  br label %bb27
+
+bb9:                                              ; preds = %bb
+  %tmp10 = udiv i32 65536, %arg2
+  br label %bb11
+
+bb11:                                             ; preds = %bb11, %bb9
+  %tmp12 = phi i32 [ %tmp20, %bb11 ], [ %tmp5, %bb9 ]
+  %tmp13 = phi float* [ %tmp18, %bb11 ], [ %tmp4, %bb9 ]
+  %tmp14 = phi i32 [ %tmp16, %bb11 ], [ %tmp10, %bb9 ]
+  %tmp15 = phi i32 [ %tmp19, %bb11 ], [ %tmp, %bb9 ]
+  %tmp16 = add nsw i32 %tmp14, -1
+  %tmp17 = sitofp i32 %tmp12 to float
+  store float %tmp17, float* %tmp13, align 4
+  %tmp18 = getelementptr inbounds float, float* %tmp13, i64 1
+  %tmp19 = add i32 %tmp15, %arg2
+  %tmp20 = and i32 %tmp19, 65535
+  %tmp21 = icmp eq i32 %tmp16, 0
+  br i1 %tmp21, label %bb22, label %bb11
+
+bb22:                                             ; preds = %bb11
+  %tmp23 = phi float* [ %tmp18, %bb11 ]
+  %tmp24 = phi i32 [ %tmp19, %bb11 ]
+  %tmp25 = phi i32 [ %tmp20, %bb11 ]
+  %tmp26 = ashr i32 %tmp24, 16
+  store i32 %tmp26, i32* @global, align 4
+  br label %bb27
+
+bb27:                                             ; preds = %bb22, %bb7
+  %tmp28 = phi i32 [ %tmp26, %bb22 ], [ %tmp8, %bb7 ]
+  %tmp29 = phi float* [ %tmp23, %bb22 ], [ %tmp4, %bb7 ]
+  %tmp30 = phi i32 [ %tmp25, %bb22 ], [ %tmp5, %bb7 ]
+  %tmp31 = sext i32 %tmp28 to i64
+  %tmp32 = getelementptr inbounds float, float* %tmp3, i64 %tmp31
+  %tmp33 = load float, float* %tmp32, align 4
+  %tmp34 = sitofp i32 %tmp30 to float
+  %tmp35 = load float, float* @global.2, align 4
+  %tmp36 = fmul float %tmp35, %tmp34
+  %tmp37 = fadd float %tmp33, %tmp36
+  store float %tmp37, float* %tmp29, align 4
+  ret void
+}
Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -5315,8 +5315,13 @@
 
   // Both the PHI node itself, and the "post-increment" value feeding
   // back into the PHI node may have external users.
-  AllowedExit.insert(Phi);
-  AllowedExit.insert(Phi->getIncomingValueForBlock(TheLoop->getLoopLatch()));
+  // We can allow those uses, except if the SCEVs we have for them rely
+  // on predicates that only hold within the loop, since allowing the exit
+  // currently means re-using this SCEV outside the loop.
+  if (PSE.getUnionPredicate().isAlwaysTrue()) {
+    AllowedExit.insert(Phi);
+    AllowedExit.insert(Phi->getIncomingValueForBlock(TheLoop->getLoopLatch()));
+  }
 
   DEBUG(dbgs() << "LV: Found an induction variable.\n");
   return;


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