For the current Atom processor, the fastest way to handle a call

indirect through a memory address is to load the memory address into
a register and then call indirect through the register.

This patch implements this improvement by modifying SelectionDAG to
force a function address which is a memory reference to be loaded
into a virtual register.

Patch by Sriram Murali.

llvm-svn: 178171

1 files changed, 45 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/atom-call-reg-indirect.ll b/llvm/test/CodeGen/X86/atom-call-reg-indirect.ll
new file mode 100644
index 00000000000..632781130d0
--- /dev/null
+++ b/llvm/test/CodeGen/X86/atom-call-reg-indirect.ll
@@ -0,0 +1,45 @@
+; RUN: llc < %s -mcpu=atom -mtriple=i686-linux  | FileCheck -check-prefix=ATOM32 %s
+; RUN: llc < %s -mcpu=core2 -mtriple=i686-linux | FileCheck -check-prefix=ATOM-NOT32 %s
+; RUN: llc < %s -mcpu=atom -mtriple=x86_64-linux  | FileCheck -check-prefix=ATOM64 %s
+; RUN: llc < %s -mcpu=core2 -mtriple=x86_64-linux | FileCheck -check-prefix=ATOM-NOT64 %s
+
+
+; fn_ptr.ll
+%class.A = type { i32 (...)** }
+
+define i32 @test1() #0 {
+  ;ATOM: test1
+entry:
+  %call = tail call %class.A* @_Z3facv()
+  %0 = bitcast %class.A* %call to void (%class.A*)***
+  %vtable = load void (%class.A*)*** %0, align 8
+  %1 = load void (%class.A*)** %vtable, align 8
+  ;ATOM32: movl (%ecx), %ecx
+  ;ATOM32: calll *%ecx
+  ;ATOM-NOT32: calll *(%ecx)
+  ;ATOM64: movq (%rcx), %rcx
+  ;ATOM64: callq *%rcx
+  ;ATOM-NOT64: callq *(%rcx)
+  tail call void %1(%class.A* %call)
+  ret i32 0
+}
+
+declare %class.A* @_Z3facv() #1
+
+; virt_fn.ll
+@p = external global void (i32)**
+
+define i32 @test2() #0 {
+  ;ATOM: test2
+entry:
+  %0 = load void (i32)*** @p, align 8
+  %1 = load void (i32)** %0, align 8
+  ;ATOM32: movl (%eax), %eax
+  ;ATOM32: calll *%eax
+  ;ATOM-NOT: calll *(%eax)
+  ;ATOM64: movq (%rax), %rax
+  ;ATOM64: callq *%rax
+  ;ATOM-NOT64: callq *(%rax)
+  tail call void %1(i32 2)
+  ret i32 0
+}