[llvm] r297989 - [InstCombine] avoid breaking up bitcasted vector min/max patterns (PR32306)

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Thu Mar 16 15:42:45 2017
New Revision: 297989

URL: http://llvm.org/viewvc/llvm-project?rev=297989&view=rev
Log:
[InstCombine] avoid breaking up bitcasted vector min/max patterns (PR32306)

As the related tests show, we're not canonicalizing to this form for scalars or vectors yet,
but this solves the immediate problem in:
https://bugs.llvm.org/show_bug.cgi?id=32306


Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp?rev=297989&r1=297988&r2=297989&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Thu Mar 16 15:42:45 2017
@@ -120,6 +120,16 @@ static Constant *getSelectFoldableConsta
 /// We have (select c, TI, FI), and we know that TI and FI have the same opcode.
 Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
                                           Instruction *FI) {
+  // Don't break up min/max patterns. The hasOneUse checks below prevent that
+  // for most cases, but vector min/max with bitcasts can be transformed. If the
+  // one-use restrictions are eased for other patterns, we still don't want to
+  // obfuscate min/max.
+  if ((match(&SI, m_SMin(m_Value(), m_Value())) ||
+       match(&SI, m_SMax(m_Value(), m_Value())) ||
+       match(&SI, m_UMin(m_Value(), m_Value())) ||
+       match(&SI, m_UMax(m_Value(), m_Value()))))
+    return nullptr;
+
   // If this is a cast from the same type, merge.
   if (TI->getNumOperands() == 1 && TI->isCast()) {
     Type *FIOpndTy = FI->getOperand(0)->getType();

Modified: llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll?rev=297989&r1=297988&r2=297989&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll Thu Mar 16 15:42:45 2017
@@ -529,15 +529,16 @@ define float @bitcast_scalar_umax(float
 }
 
 ; PR32306 - https://bugs.llvm.org/show_bug.cgi?id=32306
-; FIXME: The icmp/select form a canonical smin, so don't hide that by folding the final bitcast into the select.
+; The icmp/select form a canonical smin, so don't hide that by folding the final bitcast into the select.
 
 define <8 x float> @bitcast_vector_smin(<8 x float> %x, <8 x float> %y) {
 ; CHECK-LABEL: @bitcast_vector_smin(
 ; CHECK-NEXT:    [[BCX:%.*]] = bitcast <8 x float> %x to <8 x i32>
 ; CHECK-NEXT:    [[BCY:%.*]] = bitcast <8 x float> %y to <8 x i32>
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt <8 x i32> [[BCX]], [[BCY]]
-; CHECK-NEXT:    [[SEL_V:%.*]] = select <8 x i1> [[CMP]], <8 x float> %x, <8 x float> %y
-; CHECK-NEXT:    ret <8 x float> [[SEL_V]]
+; CHECK-NEXT:    [[SEL:%.*]] = select <8 x i1> [[CMP]], <8 x i32> [[BCX]], <8 x i32> [[BCY]]
+; CHECK-NEXT:    [[BCS:%.*]] = bitcast <8 x i32> [[SEL]] to <8 x float>
+; CHECK-NEXT:    ret <8 x float> [[BCS]]
 ;
   %bcx = bitcast <8 x float> %x to <8 x i32>
   %bcy = bitcast <8 x float> %y to <8 x i32>