Implement cpu_dispatch/cpu_specific Multiversioning

As documented here: https://software.intel.com/en-us/node/682969 and
https://software.intel.com/en-us/node/523346. cpu_dispatch multiversioning
is an ICC feature that provides for function multiversioning.

This feature is implemented with two attributes: First, cpu_specific,
which specifies the individual function versions. Second, cpu_dispatch,
which specifies the location of the resolver function and the list of
resolvable functions.

This is valuable since it provides a mechanism where the resolver's TU
can be specified in one location, and the individual implementions
each in their own translation units.

The goal of this patch is to be source-compatible with ICC, so this
implementation diverges from the ICC implementation in a few ways:
1- Linux x86/64 only: This implementation uses ifuncs in order to
properly dispatch functions. This is is a valuable performance benefit
over the ICC implementation. A future patch will be provided to enable
this feature on Windows, but it will obviously more closely fit ICC's
implementation.
2- CPU Identification functions: ICC uses a set of custom functions to identify
the feature list of the host processor. This patch uses the cpu_supports
functionality in order to better align with 'target' multiversioning.
1- cpu_dispatch function def/decl: ICC's cpu_dispatch requires that the function
marked cpu_dispatch be an empty definition. This patch supports that as well,
however declarations are also permitted, since the linker will solve the
issue of multiple emissions.

Differential Revision: https://reviews.llvm.org/D47474

llvm-svn: 337552

1 files changed, 101 insertions, 0 deletions

diff --git a/clang/test/CodeGen/attr-cpuspecific.c b/clang/test/CodeGen/attr-cpuspecific.c
new file mode 100644
index 00000000000..1b98b5dc967
--- /dev/null
+++ b/clang/test/CodeGen/attr-cpuspecific.c
@@ -0,0 +1,101 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+
+
+// Each called version should have an IFunc.
+// CHECK: @SingleVersion.ifunc = ifunc void (), void ()* ()* @SingleVersion.resolver
+// CHECK: @TwoVersions.ifunc = ifunc void (), void ()* ()* @TwoVersions.resolver
+// CHECK: @TwoVersionsSameAttr.ifunc = ifunc void (), void ()* ()* @TwoVersionsSameAttr.resolver
+// CHECK: @ThreeVersionsSameAttr.ifunc = ifunc void (), void ()* ()* @ThreeVersionsSameAttr.resolver
+
+__attribute__((cpu_specific(ivybridge)))
+void SingleVersion(void){}
+// CHECK: define void @SingleVersion.S() #[[S:[0-9]+]]
+
+__attribute__((cpu_specific(ivybridge)))
+void NotCalled(void){}
+// CHECK: define void @NotCalled.S() #[[S]]
+
+// Done before any of the implementations.
+__attribute__((cpu_dispatch(ivybridge, knl)))
+void TwoVersions(void);
+// CHECK: define void ()* @TwoVersions.resolver()
+// CHECK: call void @__cpu_indicator_init
+// CHECK: ret void ()* @TwoVersions.Z
+// CHECK: ret void ()* @TwoVersions.S
+// CHECK: call void @llvm.trap
+// CHECK: unreachable
+
+__attribute__((cpu_specific(ivybridge)))
+void TwoVersions(void){}
+// CHECK: define void @TwoVersions.S() #[[S]]
+
+__attribute__((cpu_specific(knl)))
+void TwoVersions(void){}
+// CHECK: define void @TwoVersions.Z() #[[K:[0-9]+]]
+
+__attribute__((cpu_specific(ivybridge, knl)))
+void TwoVersionsSameAttr(void){}
+// CHECK: define void @TwoVersionsSameAttr.S() #[[S]]
+// CHECK: define void @TwoVersionsSameAttr.Z() #[[K]]
+
+__attribute__((cpu_specific(atom, ivybridge, knl)))
+void ThreeVersionsSameAttr(void){}
+// CHECK: define void @ThreeVersionsSameAttr.O() #[[O:[0-9]+]]
+// CHECK: define void @ThreeVersionsSameAttr.S() #[[S]]
+// CHECK: define void @ThreeVersionsSameAttr.Z() #[[K]]
+
+void usages() {
+  SingleVersion();
+  // CHECK: @SingleVersion.ifunc()
+  TwoVersions();
+  // CHECK: @TwoVersions.ifunc()
+  TwoVersionsSameAttr();
+  // CHECK: @TwoVersionsSameAttr.ifunc()
+  ThreeVersionsSameAttr();
+  // CHECK: @ThreeVersionsSameAttr.ifunc()
+}
+
+// has an extra config to emit!
+__attribute__((cpu_dispatch(ivybridge, knl, atom)))
+void TwoVersionsSameAttr(void);
+// CHECK: define void ()* @TwoVersionsSameAttr.resolver()
+// CHECK: ret void ()* @TwoVersionsSameAttr.Z
+// CHECK: ret void ()* @TwoVersionsSameAttr.S
+// CHECK: ret void ()* @TwoVersionsSameAttr.O
+// CHECK: call void @llvm.trap
+// CHECK: unreachable
+
+__attribute__((cpu_dispatch(atom, ivybridge, knl)))
+void ThreeVersionsSameAttr(void){}
+// CHECK: define void ()* @ThreeVersionsSameAttr.resolver()
+// CHECK: call void @__cpu_indicator_init
+// CHECK: ret void ()* @ThreeVersionsSameAttr.Z
+// CHECK: ret void ()* @ThreeVersionsSameAttr.S
+// CHECK: ret void ()* @ThreeVersionsSameAttr.O
+// CHECK: call void @llvm.trap
+// CHECK: unreachable
+
+// No Cpu Specific options.
+__attribute__((cpu_dispatch(atom, ivybridge, knl)))
+void NoSpecifics(void);
+// CHECK: define void ()* @NoSpecifics.resolver()
+// CHECK: call void @__cpu_indicator_init
+// CHECK: ret void ()* @NoSpecifics.Z
+// CHECK: ret void ()* @NoSpecifics.S
+// CHECK: ret void ()* @NoSpecifics.O
+// CHECK: call void @llvm.trap
+// CHECK: unreachable
+
+__attribute__((cpu_dispatch(atom, generic, ivybridge, knl)))
+void HasGeneric(void);
+// CHECK: define void ()* @HasGeneric.resolver()
+// CHECK: call void @__cpu_indicator_init
+// CHECK: ret void ()* @HasGeneric.Z
+// CHECK: ret void ()* @HasGeneric.S
+// CHECK: ret void ()* @HasGeneric.O
+// CHECK: ret void ()* @HasGeneric.A
+// CHECK-NOT: call void @llvm.trap
+
+// CHECK: attributes #[[S]] = {{.*}}"target-features"="+avx,+cmov,+f16c,+mmx,+popcnt,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave"
+// CHECK: attributes #[[K]] = {{.*}}"target-features"="+adx,+avx,+avx2,+avx512cd,+avx512er,+avx512f,+avx512pf,+bmi,+cmov,+f16c,+fma,+lzcnt,+mmx,+movbe,+popcnt,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave"
+// CHECK: attributes #[[O]] = {{.*}}"target-features"="+cmov,+mmx,+movbe,+sse,+sse2,+sse3,+ssse3,+x87"