[PATCH] [DAGCombiner] Fix wrong folding of AND dag nodes.

[Phabricator]

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D8085

Files:
  llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/trunk/test/CodeGen/X86/and-load-fold.ll

Index: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2912,9 +2912,13 @@
                SplatBitSize = SplatBitSize * 2)
             SplatValue |= SplatValue.shl(SplatBitSize);
 
-        Constant = APInt::getAllOnesValue(BitWidth);
-        for (unsigned i = 0, n = SplatBitSize/BitWidth; i < n; ++i)
-          Constant &= SplatValue.lshr(i*BitWidth).zextOrTrunc(BitWidth);
+        // Make sure that variable 'Constant' is only set if 'SplatBitSize' is a
+        // multiple of 'BitWidth'. Otherwise, we could propagate a wrong value.
+        if (SplatBitSize % BitWidth == 0) {
+          Constant = APInt::getAllOnesValue(BitWidth);
+          for (unsigned i = 0, n = SplatBitSize/BitWidth; i < n; ++i)
+            Constant &= SplatValue.lshr(i*BitWidth).zextOrTrunc(BitWidth);
+        }
       }
     }
 
Index: llvm/trunk/test/CodeGen/X86/and-load-fold.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/and-load-fold.ll
+++ llvm/trunk/test/CodeGen/X86/and-load-fold.ll
@@ -0,0 +1,15 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=generic < %s | FileCheck %s
+
+; Verify that the DAGCombiner doesn't wrongly remove the 'and' from the dag.
+
+define i8 @foo(<4 x i8>* %V) {
+; CHECK-LABEL: foo:
+; CHECK: pand
+; CHECK: ret
+entry:
+  %Vp = bitcast <4 x i8>* %V to <3 x i8>*
+  %V3i8 = load <3 x i8>, <3 x i8>* %Vp, align 4
+  %0 = and <3 x i8> %V3i8, <i8 undef, i8 undef, i8 95>
+  %1 = extractelement <3 x i8> %0, i64 2
+  ret i8 %1
+}

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