[PATCH] D98449: [RISCV] Add isel-patterns to optimize (a < 1) and (a > -1) into bge

[Philipp Tomsich via Phabricator via llvm-commits]

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  The following code-sequence showed up in a testcase (isolated from
  SPEC2017) for if-conversion and vectorization when searching for the
  maximum in an array:
          addi    a2, zero, 1
          blt     a1, a2, .LBB0_5
  which can be expressed as `bge zero,a1,.LBB0_5`.
  
  More generally, we want to express
   - (a > -1) as (a >= 0)
   - (a < 1) as (0 >= a)
  
  This adds the required isel-patterns.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98449

Files:
  llvm/lib/Target/RISCV/RISCVInstrInfo.td


Index: llvm/lib/Target/RISCV/RISCVInstrInfo.td
===================================================================
--- llvm/lib/Target/RISCV/RISCVInstrInfo.td
+++ llvm/lib/Target/RISCV/RISCVInstrInfo.td
@@ -998,6 +998,12 @@
 def : Pat<(brcond (XLenVT (xor GPR:$cond, 1)), bb:$imm12),
           (BEQ GPR:$cond, X0, bb:$imm12)>;
 
+// Lower (a > -1) to (a >= 0) and (a < 1) to (0 >= a).
+def : Pat<(brcond (XLenVT (setlt XLenVT:$lhs, 1)), bb:$dst),
+	  (BGE X0, XLenVT:$lhs, bb:$dst)>;
+def : Pat<(brcond (XLenVT (setgt XLenVT:$lhs, -1)), bb:$dst),
+	  (BGE XLenVT:$lhs, X0, bb:$dst)>;
+
 let isBarrier = 1, isBranch = 1, isTerminator = 1 in
 def PseudoBR : Pseudo<(outs), (ins simm21_lsb0_jal:$imm20), [(br bb:$imm20)]>,
                PseudoInstExpansion<(JAL X0, simm21_lsb0_jal:$imm20)>;


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