[InstCombine] Fix incorrect rule from rL236202

The rule for SMIN introduced in rL236202 doesn't work as advertised: the
check for Pred == ICmpInst::ICMP_SGT was missing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264996 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ValueTracking.cpp

@@ -3552,7 +3552,8 @@ static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred,
 
     // Y >s C ? ~Y : ~C == ~Y <s ~C ? ~Y : ~C = SMIN(~Y, ~C)
     if (const auto *C2 = dyn_cast<ConstantInt>(FalseVal)) {
-      if (C1->getType() == C2->getType() && ~C1->getValue() == C2->getValue() &&
+      if (Pred == ICmpInst::ICMP_SGT && C1->getType() == C2->getType() &&
+          ~C1->getValue() == C2->getValue() &&
           (match(TrueVal, m_Not(m_Specific(CmpLHS))) ||
            match(CmpLHS, m_Not(m_Specific(TrueVal))))) {
         LHS = TrueVal;

test/Transforms/InstCombine/select.ll

@@ -1589,3 +1589,21 @@ define i32 @PR23757(i32 %x) {
   %sel = select i1 %cmp, i32 -2147483648, i32 %add
   ret i32 %sel
 }
+
+
+define i32 @PR27137(i32 %a) {
+; CHECK-LABEL: @PR27137(
+; CHECK-NEXT:  %not_a = xor i32 %a, -1
+; CHECK-NEXT:  %c0 = icmp slt i32 %a, 0
+; CHECK-NEXT:  %s0 = select i1 %c0, i32 %not_a, i32 -1
+; CHECK-NEXT:  %c1 = icmp sgt i32 %s0, -1
+; CHECK-NEXT:  %s1 = select i1 %c1, i32 %s0, i32 -1
+; CHECK-NEXT:  ret i32 %s1
+
+  %not_a = xor i32 %a, -1
+  %c0 = icmp slt i32 %a, 0
+  %s0 = select i1 %c0, i32 %not_a, i32 -1
+  %c1 = icmp sgt i32 %s0, -1
+  %s1 = select i1 %c1, i32 %s0, i32 -1
+  ret i32 %s1
+}