[PATCH] D98542: [RISCV] Teach normaliseSetCC to canonicalize X > -1 to X >= 0 and X < 1 to 0 >= X.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: jrtc27, asb, luismarques.
Herald added subscribers: StephenFan, vkmr, frasercrmck, evandro, apazos, sameer.abuasal, s.egerton, Jim, benna, psnobl, jocewei, PkmX, the_o, brucehoult, MartinMosbeck, rogfer01, edward-jones, zzheng, shiva0217, kito-cheng, niosHD, sabuasal, simoncook, johnrusso, rbar, hiraditya.
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This allows the use of BGE with X0 instead of puting -1/1 in a
register.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98542

Files:
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/test/CodeGen/RISCV/select-cc.ll


Index: llvm/test/CodeGen/RISCV/select-cc.ll
===================================================================
--- llvm/test/CodeGen/RISCV/select-cc.ll
+++ llvm/test/CodeGen/RISCV/select-cc.ll
@@ -58,14 +58,12 @@
 ; RV32I-NEXT:    mv a0, a2
 ; RV32I-NEXT:  .LBB0_20:
 ; RV32I-NEXT:    lw a2, 0(a1)
-; RV32I-NEXT:    addi a3, zero, 1
-; RV32I-NEXT:    blt a2, a3, .LBB0_22
+; RV32I-NEXT:    blez a2, .LBB0_22
 ; RV32I-NEXT:  # %bb.21:
 ; RV32I-NEXT:    mv a0, a2
 ; RV32I-NEXT:  .LBB0_22:
 ; RV32I-NEXT:    lw a1, 0(a1)
-; RV32I-NEXT:    addi a3, zero, -1
-; RV32I-NEXT:    blt a3, a2, .LBB0_24
+; RV32I-NEXT:    bgez a2, .LBB0_24
 ; RV32I-NEXT:  # %bb.23:
 ; RV32I-NEXT:    mv a0, a1
 ; RV32I-NEXT:  .LBB0_24:
Index: llvm/lib/Target/RISCV/RISCVISelLowering.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -822,7 +822,22 @@
 // Changes the condition code and swaps operands if necessary, so the SetCC
 // operation matches one of the comparisons supported directly in the RISC-V
 // ISA.
-static void normaliseSetCC(SDValue &LHS, SDValue &RHS, ISD::CondCode &CC) {
+static void normaliseSetCC(const SDLoc &DL, SDValue &LHS, SDValue &RHS,
+                           ISD::CondCode &CC, SelectionDAG &DAG) {
+  // Convert X > -1 to X >= 0.
+  if (CC == ISD::SETGT && isAllOnesConstant(RHS)) {
+    RHS = DAG.getConstant(0, DL, RHS.getValueType());
+    CC = ISD::SETGE;
+    return;
+  }
+  // Convert X < 1 to 0 >= X.
+  if (CC == ISD::SETLT && isOneConstant(RHS)) {
+    RHS = LHS;
+    LHS = DAG.getConstant(0, DL, RHS.getValueType());
+    CC = ISD::SETGE;
+    return;
+  }
+
   switch (CC) {
   default:
     break;
@@ -1869,7 +1884,7 @@
     auto CC = cast<CondCodeSDNode>(CondV.getOperand(2));
     ISD::CondCode CCVal = CC->get();
 
-    normaliseSetCC(LHS, RHS, CCVal);
+    normaliseSetCC(DL, LHS, RHS, CCVal, DAG);
 
     SDValue TargetCC = DAG.getConstant(CCVal, DL, XLenVT);
     SDValue Ops[] = {LHS, RHS, TargetCC, TrueV, FalseV};
@@ -4156,11 +4171,11 @@
       if (Invert)
         CCVal = ISD::getSetCCInverse(CCVal, LHS.getValueType());
 
+      SDLoc DL(N);
       RHS = LHS.getOperand(1);
       LHS = LHS.getOperand(0);
-      normaliseSetCC(LHS, RHS, CCVal);
+      normaliseSetCC(DL, LHS, RHS, CCVal, DAG);
 
-      SDLoc DL(N);
       SDValue TargetCC = DAG.getConstant(CCVal, DL, Subtarget.getXLenVT());
       return DAG.getNode(
           RISCVISD::SELECT_CC, DL, N->getValueType(0),


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