[NVVM][MLIR] Remove Pure trait from clock, clock64, globaltimer Ops

This commit removes Pure trait from clock, clock64 and globaltimer Ops by creating NVVM_NCSpecialRegisterOp class to represent Ops which return non-constant values. This prevents CSE pass from optimizing away redundant uses of them

Author: schwarzschild-radius

mlir/include/mlir/Dialect/LLVMIR/NVVMOps.td

@@ -159,6 +159,13 @@ class NVVM_SpecialRegisterOp<string mnemonic, list<Trait> traits = []> :
   let assemblyFormat = "attr-dict `:` type($res)";
 }
 
+// NVVM_NCSpecialRegisterOp represents a non-constant special register
+class NVVM_NCSpecialRegisterOp<string mnemonic, list<Trait> traits = []> :
+  NVVM_IntrOp<mnemonic, traits, 1> {
+  let arguments = (ins);
+  let assemblyFormat = "attr-dict `:` type($res)";
+}
+
 class NVVM_SpecialRangeableRegisterOp<string mnemonic, list<Trait> traits = []> :
   NVVM_SpecialRegisterOp<mnemonic,
     !listconcat(traits,
@@ -249,9 +256,9 @@ def NVVM_ClusterDim : NVVM_SpecialRangeableRegisterOp<"read.ptx.sreg.cluster.nct
 
 //===----------------------------------------------------------------------===//
 // Clock registers
-def NVVM_ClockOp : NVVM_SpecialRegisterOp<"read.ptx.sreg.clock">;
-def NVVM_Clock64Op : NVVM_SpecialRegisterOp<"read.ptx.sreg.clock64">;
-def NVVM_GlobalTimerOp : NVVM_SpecialRegisterOp<"read.ptx.sreg.globaltimer">;
+def NVVM_ClockOp : NVVM_NCSpecialRegisterOp<"read.ptx.sreg.clock">;
+def NVVM_Clock64Op : NVVM_NCSpecialRegisterOp<"read.ptx.sreg.clock64">;
+def NVVM_GlobalTimerOp : NVVM_NCSpecialRegisterOp<"read.ptx.sreg.globaltimer">;
 
 //===----------------------------------------------------------------------===//
 // envreg registers

mlir/test/Dialect/LLVMIR/cse-nvvm.mlir

@@ -0,0 +1,37 @@
+// RUN: mlir-opt %s -cse -split-input-file -verify-diagnostics | FileCheck %s
+
+// CHECK-LABEL: @nvvm_special_regs_clock
+llvm.func @nvvm_special_regs_clock() -> !llvm.struct<(i32, i32)> {
+  %0 = llvm.mlir.zero: !llvm.struct<(i32, i32)>
+  // CHECK:  {{.*}} = nvvm.read.ptx.sreg.clock
+  %1 = nvvm.read.ptx.sreg.clock : i32
+  // CHECK:  {{.*}} = nvvm.read.ptx.sreg.clock
+  %2 = nvvm.read.ptx.sreg.clock : i32
+  %4 = llvm.insertvalue %1, %0[0]: !llvm.struct<(i32, i32)>
+  %5 = llvm.insertvalue %2, %4[1]: !llvm.struct<(i32, i32)>
+  llvm.return %5: !llvm.struct<(i32, i32)>
+}
+
+// CHECK-LABEL: @nvvm_special_regs_clock64
+llvm.func @nvvm_special_regs_clock64() -> !llvm.struct<(i64, i64)> {
+  %0 = llvm.mlir.zero: !llvm.struct<(i64, i64)>
+  // CHECK:  {{.*}} = nvvm.read.ptx.sreg.clock64
+  %1 = nvvm.read.ptx.sreg.clock64 : i64
+  // CHECK:  {{.*}} = nvvm.read.ptx.sreg.clock64
+  %2 = nvvm.read.ptx.sreg.clock64 : i64
+  %4 = llvm.insertvalue %1, %0[0]: !llvm.struct<(i64, i64)>
+  %5 = llvm.insertvalue %2, %4[1]: !llvm.struct<(i64, i64)>
+  llvm.return %5: !llvm.struct<(i64, i64)>
+}
+
+// CHECK-LABEL: @nvvm_special_regs_globaltimer
+llvm.func @nvvm_special_regs_globaltimer() -> !llvm.struct<(i64, i64)> {
+  %0 = llvm.mlir.zero: !llvm.struct<(i64, i64)>
+  // CHECK:  {{.*}} = nvvm.read.ptx.sreg.globaltimer
+  %1 = nvvm.read.ptx.sreg.globaltimer : i64
+  // CHECK:  {{.*}} = nvvm.read.ptx.sreg.globaltimer
+  %2 = nvvm.read.ptx.sreg.globaltimer : i64
+  %4 = llvm.insertvalue %1, %0[0]: !llvm.struct<(i64, i64)>
+  %5 = llvm.insertvalue %2, %4[1]: !llvm.struct<(i64, i64)>
+  llvm.return %5: !llvm.struct<(i64, i64)>
+}