[NVPTX] Add builtin support for 'globaltimer' (#79765)

Summary:
This patch adds support for `globaltimer` to match `clock` and
`clock64`. See the PTX ISA reference for details. This patch does not
implement the `hi` or `lo` variants for brevity as they can be obtained
from this with the cost of an additional register.

https://docs.nvidia.com/cuda/parallel-thread-execution/index.html#special-registers-globaltimer-globaltimer-lo-globaltimer-hi

Author: jhuber6

clang/include/clang/Basic/BuiltinsNVPTX.def

@@ -148,6 +148,7 @@ BUILTIN(__nvvm_read_ptx_sreg_lanemask_gt, "i", "nc")
 
 BUILTIN(__nvvm_read_ptx_sreg_clock, "i", "n")
 BUILTIN(__nvvm_read_ptx_sreg_clock64, "LLi", "n")
+BUILTIN(__nvvm_read_ptx_sreg_globaltimer, "LLi", "n")
 
 BUILTIN(__nvvm_read_ptx_sreg_pm0, "i", "n")
 BUILTIN(__nvvm_read_ptx_sreg_pm1, "i", "n")

clang/test/CodeGen/builtins-nvptx.c

@@ -134,11 +134,13 @@ __device__ long long read_clocks() {
 
 // CHECK: call i32 @llvm.nvvm.read.ptx.sreg.clock()
 // CHECK: call i64 @llvm.nvvm.read.ptx.sreg.clock64()
+// CHECK: call i64 @llvm.nvvm.read.ptx.sreg.globaltimer()
 
   int a = __nvvm_read_ptx_sreg_clock();
   long long b = __nvvm_read_ptx_sreg_clock64();
+  long long c = __nvvm_read_ptx_sreg_globaltimer();
 
-  return a + b;
+  return a + b + c;
 }
 
 __device__ int read_pms() {

llvm/include/llvm/IR/IntrinsicsNVVM.td

@@ -4510,6 +4510,8 @@ def int_nvvm_read_ptx_sreg_lanemask_gt :
 def int_nvvm_read_ptx_sreg_clock : PTXReadNCSRegIntrinsic_r32<"clock">;
 def int_nvvm_read_ptx_sreg_clock64 : PTXReadNCSRegIntrinsic_r64<"clock64">;
 
+def int_nvvm_read_ptx_sreg_globaltimer : PTXReadNCSRegIntrinsic_r64<"globaltimer">;
+
 def int_nvvm_read_ptx_sreg_pm0 : PTXReadNCSRegIntrinsic_r32<"pm0">;
 def int_nvvm_read_ptx_sreg_pm1 : PTXReadNCSRegIntrinsic_r32<"pm1">;
 def int_nvvm_read_ptx_sreg_pm2 : PTXReadNCSRegIntrinsic_r32<"pm2">;

llvm/lib/Target/NVPTX/NVPTXIntrinsics.td

@@ -6376,6 +6376,8 @@ def INT_PTX_SREG_CLOCK :
     PTX_READ_SREG_R32<"clock", int_nvvm_read_ptx_sreg_clock>;
 def INT_PTX_SREG_CLOCK64 :
     PTX_READ_SREG_R64<"clock64", int_nvvm_read_ptx_sreg_clock64>;
+def INT_PTX_SREG_GLOBALTIMER :
+    PTX_READ_SREG_R64<"globaltimer", int_nvvm_read_ptx_sreg_globaltimer>;
 
 def INT_PTX_SREG_PM0 : PTX_READ_SREG_R32<"pm0", int_nvvm_read_ptx_sreg_pm0>;
 def INT_PTX_SREG_PM1 : PTX_READ_SREG_R32<"pm1", int_nvvm_read_ptx_sreg_pm1>;

llvm/test/CodeGen/NVPTX/intrinsics.ll

@@ -140,6 +140,17 @@ define void @test_exit() {
   ret void
 }
 
+; CHECK-LABEL: test_globaltimer
+define i64 @test_globaltimer() {
+; CHECK: mov.u64         %r{{.*}}, %globaltimer;
+  %a = tail call i64 @llvm.nvvm.read.ptx.sreg.globaltimer()
+; CHECK: mov.u64         %r{{.*}}, %globaltimer;
+  %b = tail call i64 @llvm.nvvm.read.ptx.sreg.globaltimer()
+  %ret = add i64 %a, %b
+; CHECK: ret
+  ret i64 %ret
+}
+
 declare float @llvm.fabs.f32(float)
 declare double @llvm.fabs.f64(double)
 declare float @llvm.nvvm.sqrt.f(float)
@@ -154,3 +165,4 @@ declare i32 @llvm.nvvm.read.ptx.sreg.tid.x()
 declare i32 @llvm.nvvm.read.ptx.sreg.clock()
 declare i64 @llvm.nvvm.read.ptx.sreg.clock64()
 declare void @llvm.nvvm.exit()
+declare i64 @llvm.nvvm.read.ptx.sreg.globaltimer()