[X86] Add support for builtin to read performance monitoring counters.

This patch adds support for a new builtin instruction called
__builtin_ia32_rdpmc.

Builtin '__builtin_ia32_rdpmc' is defined as a 'GCC builtin'; on X86, it can
be used to read performance monitoring counters. It takes as input the index
of the performance counter to read, and returns the value of the specified
performance counter as a 64-bit number.

Calls to this new builtin will map to instruction RDPMC.
The index in input to the builtin call is moved to register %ECX. The result
of the builtin call is the value of the specified performance counter (RDPMC
would return that quantity in registers RDX:RAX).

This patch:
 - Adds builtin int_x86_rdpmc as a GCCBuiltin;
 - Adds a new x86 DAG node called 'RDPMC_DAG';
 - Teaches how to lower this new builtin;
 - Adds an ISel pattern to select instruction RDPMC;
 - Fixes the definition of instruction RDPMC adding %RAX and %RDX as
   implicit definitions, and adding %ECX as implicit use;
 - Adds a LLVM test to verify that the new builtin is correctly selected.

llvm-svn: 212049

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86InstrSystem.td b/llvm/lib/Target/X86/X86InstrSystem.td
index b5595cbd3bb..540278021f0 100644
--- a/llvm/lib/Target/X86/X86InstrSystem.td
+++ b/llvm/lib/Target/X86/X86InstrSystem.td
@@ -439,7 +439,10 @@ def LLDT16m : I<0x00, MRM2m, (outs), (ins i16mem:$src),
 let SchedRW = [WriteSystem] in {
 def WRMSR : I<0x30, RawFrm, (outs), (ins), "wrmsr", [], IIC_WRMSR>, TB;
 def RDMSR : I<0x32, RawFrm, (outs), (ins), "rdmsr", [], IIC_RDMSR>, TB;
-def RDPMC : I<0x33, RawFrm, (outs), (ins), "rdpmc", [], IIC_RDPMC>, TB;
+
+let Defs = [RAX, RDX], Uses = [ECX] in
+  def RDPMC : I<0x33, RawFrm, (outs), (ins), "rdpmc", [(X86rdpmc)], IIC_RDPMC>,
+              TB;
 
 def SMSW16r : I<0x01, MRM4r, (outs GR16:$dst), (ins), 
                 "smsw{w}\t$dst", [], IIC_SMSW>, OpSize16, TB;