[clang] [llvm] [SPIRV][HLSL] Add lowering of `rsqrt` to SPIRV (PR #95849)

[Farzon Lotfi via cfe-commits]

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+; RUN: llc -O0 -mtriple=spirv-unknown-unknown %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv-unknown-unknown %s -o - -filetype=obj | spirv-val %}
+
+; CHECK: OpExtInstImport "GLSL.std.450"
+
+define noundef float @rsqrt_float(float noundef %a) {
+entry:
+; CHECK: %[[#]] = OpExtInst %[[#]] %[[#]] InverseSqrt %[[#]]
+  %elt.rsqrt = call float @llvm.spv.rsqrt.f32(float %a)
+  ret float %elt.rsqrt
+}
+
+define noundef half @rsqrt_half(half noundef %a) {
+entry:
+; CHECK: %[[#]] = OpExtInst %[[#]] %[[#]] InverseSqrt %[[#]]
+  %elt.rsqrt = call half @llvm.spv.rsqrt.f16(half %a)
+  ret half %elt.rsqrt
+}
+
+define noundef double @rsqrt_double(double noundef %a) {
+entry:
+; CHECK: %[[#]] = OpExtInst %[[#]] %[[#]] InverseSqrt %[[#]]
+  %elt.rsqrt = call double @llvm.spv.rsqrt.f64(double %a)
+  ret double %elt.rsqrt
+}
+
+declare half @llvm.spv.sqrt.f16(half)
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farzonl wrote:

add vector tests, spirv backedn supports vectors so we might aswell add those tests.

https://github.com/llvm/llvm-project/pull/95849