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
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index a256eb1..b6d30a9 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -8904,11 +8904,10 @@
return EmitX86CpuSupports(FeatureStr);
}
-Value *CodeGenFunction::EmitX86CpuSupports(ArrayRef<StringRef> FeatureStrs) {
+uint32_t
+CodeGenFunction::GetX86CpuSupportsMask(ArrayRef<StringRef> FeatureStrs) {
// Processor features and mapping to processor feature value.
-
uint32_t FeaturesMask = 0;
-
for (const StringRef &FeatureStr : FeatureStrs) {
unsigned Feature =
StringSwitch<unsigned>(FeatureStr)
@@ -8917,7 +8916,14 @@
;
FeaturesMask |= (1U << Feature);
}
+ return FeaturesMask;
+}
+Value *CodeGenFunction::EmitX86CpuSupports(ArrayRef<StringRef> FeatureStrs) {
+ return EmitX86CpuSupports(GetX86CpuSupportsMask(FeatureStrs));
+}
+
+llvm::Value *CodeGenFunction::EmitX86CpuSupports(uint32_t FeaturesMask) {
// Matching the struct layout from the compiler-rt/libgcc structure that is
// filled in:
// unsigned int __cpu_vendor;