[llvm] r185081 - LoopVectorize: Use vectorized loop invariant gep index anchored in loop

[Arnold Schwaighofer]

Author: arnolds
Date: Thu Jun 27 10:11:55 2013
New Revision: 185081

URL: http://llvm.org/viewvc/llvm-project?rev=185081&view=rev
Log:
LoopVectorize: Use vectorized loop invariant gep index anchored in loop

Use vectorized instruction instead of original instruction anchored in the
original loop.

Fixes PR16452 and t2075.c of PR16455.

Added:
    llvm/trunk/test/Transforms/LoopVectorize/undef-inst-bug.ll
Modified:
    llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp

Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=185081&r1=185080&r2=185081&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Thu Jun 27 10:11:55 2013
@@ -1205,16 +1205,28 @@ void InnerLoopVectorizer::vectorizeMemor
     // The last index does not have to be the induction. It can be
     // consecutive and be a function of the index. For example A[I+1];
     unsigned NumOperands = Gep->getNumOperands();
-
-    Value *LastGepOperand = Gep->getOperand(NumOperands - 1);
-    VectorParts &GEPParts = getVectorValue(LastGepOperand);
-    Value *LastIndex = GEPParts[0];
-    LastIndex = Builder.CreateExtractElement(LastIndex, Zero);
-
+    unsigned LastOperand = NumOperands - 1;
     // Create the new GEP with the new induction variable.
     GetElementPtrInst *Gep2 = cast<GetElementPtrInst>(Gep->clone());
-    Gep2->setOperand(NumOperands - 1, LastIndex);
-    Gep2->setName("gep.indvar.idx");
+
+    for (unsigned i = 0; i < NumOperands; ++i) {
+      Value *GepOperand = Gep->getOperand(i);
+      Instruction *GepOperandInst = dyn_cast<Instruction>(GepOperand);
+
+      // Update last index or loop invariant instruction anchored in loop.
+      if (i == LastOperand ||
+          (GepOperandInst && OrigLoop->contains(GepOperandInst))) {
+        assert((i == LastOperand ||
+               SE->isLoopInvariant(SE->getSCEV(GepOperandInst), OrigLoop)) &&
+               "Must be last index or loop invariant");
+
+        VectorParts &GEPParts = getVectorValue(GepOperand);
+        Value *Index = GEPParts[0];
+        Index = Builder.CreateExtractElement(Index, Zero);
+        Gep2->setOperand(i, Index);
+        Gep2->setName("gep.indvar.idx");
+      }
+    }
     Ptr = Builder.Insert(Gep2);
   } else {
     // Use the induction element ptr.

Added: llvm/trunk/test/Transforms/LoopVectorize/undef-inst-bug.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/undef-inst-bug.ll?rev=185081&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/undef-inst-bug.ll (added)
+++ llvm/trunk/test/Transforms/LoopVectorize/undef-inst-bug.ll Thu Jun 27 10:11:55 2013
@@ -0,0 +1,36 @@
+; RUN: opt -S -loop-vectorize -force-vector-width=4 -force-vector-unroll=1 < %s | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+; We use to fail on this loop because we did not properly handle the loop
+; invariant instruction anchored in the loop when used as a getelementptr index.
+; We would use the index from the original loop resulting in a use not dominated
+; by the definition.
+
+; PR16452
+
+; Verify that we don't miscompile this loop.
+
+; CHECK: @t
+; CHECK: <4 x i32>
+
+define void @t() {
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv17 = phi i64 [ %indvars.next, %for.body ], [ 128, %entry ]
+
+  ; Loop invariant anchored in loop.
+  %idxprom21 = zext i32 undef to i64
+
+  %arrayidx23 = getelementptr inbounds [100 x [100 x i32]]* undef, i64 0, i64 %idxprom21, i64 %indvars.iv17
+  store i32 undef, i32* %arrayidx23, align 4
+  %indvars.next= add i64 %indvars.iv17, -1
+  %0 = trunc i64 %indvars.next to i32
+  %cmp15 = icmp ugt i32 %0, undef
+  br i1 %cmp15, label %for.body, label %loopexit
+
+loopexit:
+  ret void
+}