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

Nitin John Raj via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Mon Aug 28 10:47:54 PDT 2023

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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.

  rG LLVM Github Monorepo



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