[PATCH] D22114: [InstCombine] extend vector select matching for non-splat constants

[Sanjay Patel via llvm-commits]

spatel created this revision.
spatel added reviewers: eli.friedman, majnemer, RKSimon.
spatel added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

In D21740, we discussed trying to make this a more general matcher. However, I didn't see a clean way to handle the regular m_Not cases and these non-splat vector patterns, so I've just opted for the direct approach here. If there are other potential uses of areInverseVectorBitmasks(), we could move that to a higher level.

http://reviews.llvm.org/D22114

Files:
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  test/Transforms/InstCombine/logical-select.ll

Index: test/Transforms/InstCombine/logical-select.ll
===================================================================
--- test/Transforms/InstCombine/logical-select.ll
+++ test/Transforms/InstCombine/logical-select.ll
@@ -308,10 +308,8 @@
 
 define <4 x i32> @vec_sel_consts(<4 x i32> %a, <4 x i32> %b) {
 ; CHECK-LABEL: @vec_sel_consts(
-; CHECK-NEXT:    [[AND1:%.*]] = and <4 x i32> %a, <i32 -1, i32 0, i32 0, i32 -1>
-; CHECK-NEXT:    [[AND2:%.*]] = and <4 x i32> %b, <i32 0, i32 -1, i32 -1, i32 0>
-; CHECK-NEXT:    [[OR:%.*]] = or <4 x i32> [[AND1]], [[AND2]]
-; CHECK-NEXT:    ret <4 x i32> [[OR]]
+; CHECK-NEXT:    [[TMP1:%.*]] = select <4 x i1> <i1 true, i1 false, i1 false, i1 true>, <4 x i32> %a, <4 x i32> %b
+; CHECK-NEXT:    ret <4 x i32> [[TMP1]]
 ;
   %and1 = and <4 x i32> %a, <i32 -1, i32 0, i32 0, i32 -1>
   %and2 = and <4 x i32> %b, <i32 0, i32 -1, i32 -1, i32 0>
@@ -323,10 +321,8 @@
 
 define <3 x i129> @vec_sel_consts_weird(<3 x i129> %a, <3 x i129> %b) {
 ; CHECK-LABEL: @vec_sel_consts_weird(
-; CHECK-NEXT:    [[AND1:%.*]] = and <3 x i129> %a, <i129 -1, i129 0, i129 -1>
-; CHECK-NEXT:    [[AND2:%.*]] = and <3 x i129> %b, <i129 0, i129 -1, i129 0>
-; CHECK-NEXT:    [[OR:%.*]] = or <3 x i129> [[AND2]], [[AND1]]
-; CHECK-NEXT:    ret <3 x i129> [[OR]]
+; CHECK-NEXT:    [[TMP1:%.*]] = select <3 x i1> <i1 false, i1 true, i1 false>, <3 x i129> %b, <3 x i129> %a
+; CHECK-NEXT:    ret <3 x i129> [[TMP1]]
 ;
   %and1 = and <3 x i129> %a, <i129 -1, i129 0, i129 -1>
   %and2 = and <3 x i129> %b, <i129 0, i129 -1, i129 0>
@@ -353,13 +349,8 @@
 
 define <4 x i32> @vec_sel_xor(<4 x i32> %a, <4 x i32> %b, <4 x i1> %c) {
 ; CHECK-LABEL: @vec_sel_xor(
-; CHECK-NEXT:    [[MASK:%.*]] = sext <4 x i1> %c to <4 x i32>
-; CHECK-NEXT:    [[MASK_FLIP1:%.*]] = xor <4 x i32> [[MASK]], <i32 -1, i32 0, i32 0, i32 0>
-; CHECK-NEXT:    [[NOT_MASK_FLIP1:%.*]] = xor <4 x i32> [[MASK]], <i32 0, i32 -1, i32 -1, i32 -1>
-; CHECK-NEXT:    [[AND1:%.*]] = and <4 x i32> [[NOT_MASK_FLIP1]], %a
-; CHECK-NEXT:    [[AND2:%.*]] = and <4 x i32> [[MASK_FLIP1]], %b
-; CHECK-NEXT:    [[OR:%.*]] = or <4 x i32> [[AND1]], [[AND2]]
-; CHECK-NEXT:    ret <4 x i32> [[OR]]
+; CHECK-NEXT:    [[TMP1:%.*]] = select <4 x i1> %c, <4 x i32> %a, <4 x i32> %b
+; CHECK-NEXT:    ret <4 x i32> [[TMP1]]
 ;
   %mask = sext <4 x i1> %c to <4 x i32>
   %mask_flip1 = xor <4 x i32> %mask, <i32 -1, i32 0, i32 0, i32 0>
Index: lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1589,6 +1589,23 @@
   return LastInst;
 }
 
+/// If all elements of two constant vectors are 0/-1 and inverses, return true.
+static bool areInverseVectorBitmasks(Constant *C1, Constant *C2) {
+  unsigned NumElts = C1->getType()->getVectorNumElements();
+  for (unsigned i = 0; i != NumElts; ++i) {
+    Constant *EltC1 = C1->getAggregateElement(i);
+    Constant *EltC2 = C2->getAggregateElement(i);
+    if (!EltC1 || !EltC2)
+      return false;
+
+    // One element must be all ones, and the other must be all zeros.
+    if (!((match(EltC1, m_Zero()) && match(EltC2, m_AllOnes())) ||
+          (match(EltC2, m_Zero()) && match(EltC1, m_AllOnes()))))
+      return false;
+  }
+  return true;
+}
+
 /// We have an expression of the form (A & C) | (B & D). If A is a scalar or
 /// vector composed of all-zeros or all-ones values and is the bitwise 'not' of
 /// B, it can be used as the condition operand of a select instruction.
@@ -1606,7 +1623,24 @@
                            m_SExt(m_Not(m_Specific(Cond))))))
     return Cond;
 
-  // TODO: Try more matches that only apply to non-splat constant vectors.
+  // All scalar (and most vector) possibilities should be handled now.
+  // Try more matches that only apply to non-splat constant vectors.
+  if (!Ty->isVectorTy())
+    return nullptr;
+
+  // If both operands are constants, see if the constants are inverse bitmasks.
+  Constant *AC, *BC;
+  if (match(A, m_Constant(AC)) && match(B, m_Constant(BC)) &&
+      areInverseVectorBitmasks(AC, BC))
+    return ConstantExpr::getTrunc(AC, CmpInst::makeCmpResultType(Ty));
+
+  // If both operands are xor'd with constants using the same sexted boolean
+  // operand, see if the constants are inverse bitmasks.
+  if (match(A, m_Xor(m_SExt(m_Value(Cond)), m_Constant(AC))) &&
+      match(B, m_Xor(m_SExt(m_Specific(Cond)), m_Constant(BC))) &&
+      Cond->getType()->getScalarType()->isIntegerTy(1) &&
+      areInverseVectorBitmasks(AC, BC))
+    return Cond;
 
   return nullptr;
 }


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