[X86] Turn setne X, signedmin into setgt X, signedmin in LowerVSETCC to avoid an invert

[craig.topper]

Summary

This will fix one of the regressions from D42948.

[spatel]

LGTM.

llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

if (BC0.getOpcode() == ISD::AND) {
         if (llvm::all_of(EltBits, [](APInt &V) { return V.isPowerOf2(); })) {
           Cond = ISD::SETEQ;
           Op1 = DAG.getBitcast(VT, BC0.getOperand(1));
         }
       }
     }
   }
 
+  // If this is a SETNE against the signed minimum value, change it to SETGT.
+  // Otherwise we use PCMPEQ+invert.
+  APInt ConstValue;
+  if (Cond == ISD::SETNE &&
+      ISD::isConstantSplatVector(Op1.getNode(), ConstValue),
+      ConstValue.isMinSignedValue()) {
+    Cond = ISD::SETGT;
+  }
+
   // If both operands are known non-negative, then an unsigned compare is the
   // same as a signed compare and there's no need to flip signbits.
   // TODO: We could check for more general simplifications here since we're
   // computing known bits.
   bool FlipSigns = ISD::isUnsignedIntSetCC(Cond) &&
                    !(DAG.SignBitIsZero(Op0) && DAG.SignBitIsZero(Op1));
 
   // Special case: Use min/max operations for unsigned compares. We only want

llvm/trunk/test/CodeGen/X86/vector-compare-simplify.ll

 ; CHECK-NEXT:    pcmpeqd %xmm0, %xmm0
 ; CHECK-NEXT:    pxor %xmm1, %xmm0
 ; CHECK-NEXT:    retq
   %cmp = icmp uge <4 x i32> %x, <i32 -2147483648, i32 -2147483648, i32 -2147483648, i32 -2147483648>
   %r = sext <4 x i1> %cmp to <4 x i32>
   ret <4 x i32> %r
 }
 
+; Make sure we can efficiently handle ne smin by turning into sgt.
+define <4 x i32> @ne_smin(<4 x i32> %x) {
+; CHECK-LABEL: ne_smin:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pcmpgtd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %cmp = icmp ne <4 x i32> %x, <i32 -2147483648, i32 -2147483648, i32 -2147483648, i32 -2147483648>
+  %r = sext <4 x i1> %cmp to <4 x i32>
+  ret <4 x i32> %r
+}
+