[ValueTracking] recognize even more variants of smin/smax

Similar to:
https://reviews.llvm.org/rL285499
https://reviews.llvm.org/rL286318

We can't minimally expose this in IR tests because we don't have min/max intrinsics,
but the difference is visible in codegen because SelectionDAGBuilder::visitSelect() 
uses matchSelectPattern().

We're not canonicalizing these patterns in IR (yet), so I don't expect there to be any
regressions as noted here:
http://lists.llvm.org/pipermail/llvm-dev/2016-November/106868.html

llvm-svn: 286776

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5a6ca943638..18117f66a34 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3861,6 +3861,26 @@ static SelectPatternResult matchMinMax(CmpInst::Predicate Pred,
   if (Pred != CmpInst::ICMP_SGT && Pred != CmpInst::ICMP_SLT)
     return {SPF_UNKNOWN, SPNB_NA, false};
 
+  // Z = X -nsw Y
+  // (X >s Y) ? 0 : Z ==> (Z >s 0) ? 0 : Z ==> SMIN(Z, 0)
+  // (X <s Y) ? 0 : Z ==> (Z <s 0) ? 0 : Z ==> SMAX(Z, 0)
+  if (match(TrueVal, m_Zero()) &&
+      match(FalseVal, m_NSWSub(m_Specific(CmpLHS), m_Specific(CmpRHS)))) {
+    LHS = TrueVal;
+    RHS = FalseVal;
+    return {Pred == CmpInst::ICMP_SGT ? SPF_SMIN : SPF_SMAX, SPNB_NA, false};
+  }
+
+  // Z = X -nsw Y
+  // (X >s Y) ? Z : 0 ==> (Z >s 0) ? Z : 0 ==> SMAX(Z, 0)
+  // (X <s Y) ? Z : 0 ==> (Z <s 0) ? Z : 0 ==> SMIN(Z, 0)
+  if (match(FalseVal, m_Zero()) &&
+      match(TrueVal, m_NSWSub(m_Specific(CmpLHS), m_Specific(CmpRHS)))) {
+    LHS = TrueVal;
+    RHS = FalseVal;
+    return {Pred == CmpInst::ICMP_SGT ? SPF_SMAX : SPF_SMIN, SPNB_NA, false};
+  }
+
   const APInt *C1;
   if (!match(CmpRHS, m_APInt(C1)))
     return {SPF_UNKNOWN, SPNB_NA, false};