ARM: spot SBFX-compatbile code expressed with sign_extend_inreg

We were assuming all SBFX-like operations would have the shl/asr form, but
often when the field being extracted is an i8 or i16, we end up with a
SIGN_EXTEND_INREG acting on a shift instead. Simple enough to check for though.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213754 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/ARM/sbfx.ll

@@ -45,3 +45,21 @@ entry:
     %tmp2 = ashr i32 %tmp, 1
     ret i32 %tmp2
 }
+
+define signext i8 @f6(i32 %a) {
+; CHECK-LABEL: f6:
+; CHECK: sbfx r0, r0, #23, #8
+
+  %tmp = lshr i32 %a, 23
+  %res = trunc i32 %tmp to i8
+  ret i8 %res
+}
+
+define signext i8 @f7(i32 %a) {
+; CHECK-LABEL: f7:
+; CHECK-NOT: sbfx
+
+  %tmp = lshr i32 %a, 25
+  %res = trunc i32 %tmp to i8
+  ret i8 %res
+}

test/CodeGen/Thumb2/thumb2-sxt_rot.ll

@@ -10,8 +10,7 @@ define i32 @test0(i8 %A) {
 
 define signext i8 @test1(i32 %A)  {
 ; CHECK-LABEL: test1:
-; CHECK: lsrs r0, r0, #8
-; CHECK: sxtb r0, r0
+; CHECK: sbfx r0, r0, #8, #8
 	%B = lshr i32 %A, 8
 	%C = shl i32 %A, 24
 	%D = or i32 %B, %C