DAGCombine: Also shrink eq compares where the constant is exactly as …

…large as the smaller type.

if ((x & 255) == 255)

before: movzbl  %al, %eax
        cmpl  $255, %eax

after:  cmpb  $-1, %al

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182038 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -1160,7 +1160,7 @@ TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
       }
 
       // Make sure we're not losing bits from the constant.
-      if (MinBits < C1.getBitWidth() && MinBits > C1.getActiveBits()) {
+      if (MinBits < C1.getBitWidth() && MinBits >= C1.getActiveBits()) {
         EVT MinVT = EVT::getIntegerVT(*DAG.getContext(), MinBits);
         if (isTypeDesirableForOp(ISD::SETCC, MinVT)) {
           // Will get folded away.

test/CodeGen/X86/shrink-compare.ll

@@ -34,3 +34,19 @@ if.end:
 ; CHECK: test2:
 ; CHECK: cmpb $47, %{{dil|cl}}
 }
+
+define void @test3(i32 %X) nounwind {
+entry:
+  %and = and i32 %X, 255
+  %cmp = icmp eq i32 %and, 255
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  tail call void @bar() nounwind
+  br label %if.end
+
+if.end:
+  ret void
+; CHECK: test3:
+; CHECK: cmpb $-1, %{{dil|cl}}
+}