Chained comparison of two integers against a constant is not coalesced

[pedrobsaila]

Fixes #101347

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[neon-sunset]

Seems to have regressions on arm64 too 😢 I suppose Clang/LLVM reasons about these in a more generalized way...

612735.dasm - Program:InstanceMethodTest():ubyte (FullOpts)
@@ -174,11 +174,14 @@ G_M34320_IG08:        ; bbWeight=1, gcrefRegs=0000 {}, byrefRegs=0000 {}, byref
             ldr     x3, [x3]
             blr     x3
             ; gcrRegs -[x1-x2 x22]
-            cmn     w20, #1
+            movn    w0, #41
+            eor     w0, w21, w0
+            movn    w1, #0
+            eor     w1, w20, w1
+            orr     w0, w0, w1
+            cmp     w0, #0
             cset    x0, eq
-            cmn     w21, #42
-            csel    w0, wzr, w0, ne
-						;; size=88 bbWeight=1 PerfScore 16.00
+						;; size=100 bbWeight=1 PerfScore 17.50

[pedrobsaila]

It seems the regressions happen on ARM because it already supports conditional select in assembly which prevents from creating branches. Our optimization seems to confuse the JIT from recognizing the pattern and using the csel in certain methods.