[NVPTX] Lower loads from global constants using ld.global.nc (aka LDG).

Summary:
After D43914, loads from global variables in addrspace(1) happen with
ld.global.  But since they're constants, even better would be to use
ld.global.nc, aka ldg.

Reviewers: tra

Subscribers: jholewinski, sanjoy, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D43915

llvm-svn: 326390

1 files changed, 29 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/NVPTX/read-global-variable-constant.ll b/llvm/test/CodeGen/NVPTX/read-global-variable-constant.ll
new file mode 100644
index 00000000000..cb9e6dc3a45
--- /dev/null
+++ b/llvm/test/CodeGen/NVPTX/read-global-variable-constant.ll
@@ -0,0 +1,29 @@
+; RUN: llc < %s -march=nvptx -mcpu=sm_35 | FileCheck %s
+
+; Check load from constant global variables.  These loads should be
+; ld.global.nc (aka ldg).
+
+@gv_float = external constant float
+@gv_float2 = external constant <2 x float>
+@gv_float4 = external constant <4 x float>
+
+; CHECK-LABEL: test_gv_float()
+define float @test_gv_float() {
+; CHECK: ld.global.nc.f32
+  %v = load float, float* @gv_float
+  ret float %v
+}
+
+; CHECK-LABEL: test_gv_float2()
+define <2 x float> @test_gv_float2() {
+; CHECK: ld.global.nc.v2.f32
+  %v = load <2 x float>, <2 x float>* @gv_float2
+  ret <2 x float> %v
+}
+
+; CHECK-LABEL: test_gv_float4()
+define <4 x float> @test_gv_float4() {
+; CHECK: ld.global.nc.v4.f32
+  %v = load <4 x float>, <4 x float>* @gv_float4
+  ret <4 x float> %v
+}