[PATCH] D158907: [RISCV][GlobalISel] Select G_ICMP, G_IMPLICIT_DEF

[Nitin John Raj via Phabricator via llvm-commits]

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Handling the `G_ICMP ugt %x -1` case



================
Comment at: llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp:231
+
+    if (!buildLTImm(TmpReg, SrcReg1, Imm + 1, IsSigned))
+      return false;
----------------
There's a corner case here for Predicate::ICMP_UGT with Imm=-1. That compare should return false because nothing is larger than -1, but if you increment it and turn it into ICMP_ULT with imm 0 followed by XOR, it would always produce true.


RISCV ISA only has instructions for checking if a number is less than another. We select for all conditional codes in terms of these.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D158907

Files:
  llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp
  llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/cmp32.mir
  llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/cmp64.mir
  llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/implicit-def32.mir
  llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/implicit-def64.mir

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