[PATCH] D142281: [AVR] Optimize 16-bit comparison with a constant

[Ben Shi via Phabricator via llvm-commits]

benshi001 added inline comments.


================
Comment at: llvm/lib/Target/AVR/AVRISelLowering.cpp:659
+    if (Imm != 0)
+      llvm_unreachable("unexpected i16 comparison node");
+    // Generate a CPI/CPC pair.
----------------
Only a zero constant with be put at left by previous DAG transform, all other non-zero constant are dropped as RHS. So we have to handle it specially.


================
Comment at: llvm/test/CodeGen/AVR/cmp.ll:212
+; CHECK-NEXT:    cpc r1, r25
+; CHECK-NEXT:    brlt
+  %2 = icmp sgt i16 %0, 0
----------------
`x > 0` is compiled to `0 < x`, and the low 0 value byte and the high 0 value byte are represented by the zero register.


Repository:
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  https://reviews.llvm.org/D142281/new/

https://reviews.llvm.org/D142281