[llvm] [RISCV] Add short forward branch support for `lb`, `lbu`, `lh`, `lhu`, `lw`, `lwu` and `ld` (PR #170829)

[Craig Topper via llvm-commits]

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@@ -897,6 +897,80 @@ MachineInstr *RISCVInstrInfo::foldMemoryOperandImpl(
       .addImm(0);
 }
 
+unsigned getLoadPredicatedOpcode(unsigned Opcode) {
+  switch (Opcode) {
+  case RISCV::LB:
+    return RISCV::PseudoCCLB;
+  case RISCV::LBU:
+    return RISCV::PseudoCCLBU;
+  case RISCV::LH:
+    return RISCV::PseudoCCLH;
+  case RISCV::LHU:
+    return RISCV::PseudoCCLHU;
+  case RISCV::LW:
+    return RISCV::PseudoCCLW;
+  case RISCV::LWU:
+    return RISCV::PseudoCCLWU;
+  case RISCV::LD:
+    return RISCV::PseudoCCLD;
+  default:
+    return 0;
+  }
+}
+
+MachineInstr *RISCVInstrInfo::foldMemoryOperandImpl(
+    MachineFunction &MF, MachineInstr &MI, ArrayRef<unsigned> Ops,
+    MachineBasicBlock::iterator InsertPt, MachineInstr &LoadMI,
+    LiveIntervals *LIS) const {
+  // For now, only handle RISCV::PseudoCCMOVGPR.
+  if (MI.getOpcode() != RISCV::PseudoCCMOVGPR)
+    return nullptr;
+
+  if (!STI.hasShortForwardBranchILoad() ||
+      (LoadMI.getOpcode() != RISCV::LB && LoadMI.getOpcode() != RISCV::LBU &&
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topperc wrote:

Can we move the call to `getLoadPredicatedOpcode` earlier and the return value of 0 to detect unsupported cases? Then we don't need to list all 7 opcodes in two places.

https://github.com/llvm/llvm-project/pull/170829