[llvm] 48c20e7 - [RISCV][VLOPT] Do not optimize VL when isVectorOpUsedAsScalarOp (#120291)

[via llvm-commits]

Author: Michael Maitland
Date: 2024-12-17T16:10:02-05:00
New Revision: 48c20e7106bb15398b55a13d0a2ec74cb51d055e

URL: https://github.com/llvm/llvm-project/commit/48c20e7106bb15398b55a13d0a2ec74cb51d055e
DIFF: https://github.com/llvm/llvm-project/commit/48c20e7106bb15398b55a13d0a2ec74cb51d055e.diff

LOG: [RISCV][VLOPT] Do not optimize VL when isVectorOpUsedAsScalarOp (#120291)

This does not have tests, so we will remove this for now and add it back
later with tests.

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
index bd48d730a5704b..a9e5bb6ecd9b8a 100644
--- a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
+++ b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
@@ -887,13 +887,10 @@ bool RISCVVLOptimizer::checkUsers(const MachineOperand *&CommonVL,
     // Instructions like reductions may use a vector register as a scalar
     // register. In this case, we should treat it like a scalar register which
     // does not impact the decision on whether to optimize VL.
+    // TODO: Treat it like a scalar register instead of bailing out.
     if (isVectorOpUsedAsScalarOp(UserOp)) {
-      [[maybe_unused]] Register R = UserOp.getReg();
-      [[maybe_unused]] const TargetRegisterClass *RC = MRI->getRegClass(R);
-      assert(RISCV::VRRegClass.hasSubClassEq(RC) &&
-             "Expect LMUL 1 register class for vector as scalar operands!");
-      LLVM_DEBUG(dbgs() << "    Use this operand as a scalar operand\n");
-      continue;
+      CanReduceVL = false;
+      break;
     }
 
     if (mayReadPastVL(UserMI)) {