From: Sanjay Patel <spatel@rotateright.com>
Date: Thu, 16 Mar 2017 20:42:45 +0000 (+0000)
Subject: [InstCombine] avoid breaking up bitcasted vector min/max patterns (PR32306)
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=4616521acae6334c3c53d29eb7e02aa4c080ca8b;p=llvm

[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



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297989 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index b8c1daab3f6..84dace5db76 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -120,6 +120,16 @@ static Constant *getSelectFoldableConstant(Instruction *I) {
 /// 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();
diff --git a/test/Transforms/InstCombine/minmax-fold.ll b/test/Transforms/InstCombine/minmax-fold.ll
index bdb6d09ae06..19a7341fdc2 100644
--- a/test/Transforms/InstCombine/minmax-fold.ll
+++ b/test/Transforms/InstCombine/minmax-fold.ll
@@ -529,15 +529,16 @@ define float @bitcast_scalar_umax(float %x, float %y) {
 }
 
 ; 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>