[PowerPC] Fix calls to non-function objects

Looking at r225438 inspired me to see how the PowerPC backend handled the
situation (calling a bitcasted TLS global), and it turns out we also produced
an error (cannot select ...). What it means to "call" something that is not a
function is implementation and platform specific, but in the name of doing
something (besides crashing), this makes sure we do what GCC does (treat all
such calls as calls through a function pointer -- meaning that the pointer is
assumed, as is the convention on PPC, to point to a function descriptor
structure holding the actual code address along with the function's TOC pointer
and environment pointer). As GCC does, we now do the same for calling regular
(non-TLS) non-function globals too.

I'm not sure whether this is the most useful way to define the behavior, but at
least we won't be alone.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225617 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/PowerPC/ppc64-nonfunc-calls.ll

@@ -0,0 +1,69 @@
+; RUN: llc -mcpu=ppc64 < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+%struct.cd = type { i64, i64, i64 }
+
+@something = global [33 x i8] c"this is not really code, but...\0A\00", align 1
+@tls_something = thread_local global %struct.cd zeroinitializer, align 8
+@extern_something = external global %struct.cd
+
+; Function Attrs: nounwind
+define void @foo() #0 {
+entry:
+  tail call void bitcast ([33 x i8]* @something to void ()*)() #0
+  ret void
+
+; CHECK-LABEL: @foo
+; CHECK-DAG: addis [[REG1:[0-9]+]], 2, something@toc@ha
+; CHECK-DAG: std 2, 40(1)
+; CHECK-DAG: addi [[REG3:[0-9]+]], [[REG1]], something@toc@l
+; CHECK-DAG: ld [[REG2:[0-9]+]], 0([[REG3]])
+; CHECK-DAG: ld 11, 16([[REG3]])
+; CHECK-DAG: ld 2, 8([[REG3]])
+; CHECK-DAG: mtctr [[REG2]]
+; CHECK: bctrl
+; CHECK: ld 2, 40(1)
+; CHECK: blr
+}
+
+; Function Attrs: nounwind
+define void @bar() #0 {
+entry:
+  tail call void bitcast (%struct.cd* @tls_something to void ()*)() #0
+  ret void
+
+; CHECK-LABEL: @bar
+; CHECK-DAG: addis [[REG1:[0-9]+]], 13, tls_something@tprel@ha
+; CHECK-DAG: std 2, 40(1)
+; CHECK-DAG: addi [[REG3:[0-9]+]], [[REG1]], tls_something@tprel@l
+; CHECK-DAG: ld [[REG2:[0-9]+]], 0([[REG3]])
+; CHECK-DAG: ld 11, 16([[REG3]])
+; CHECK-DAG: ld 2, 8([[REG3]])
+; CHECK-DAG: mtctr [[REG2]]
+; CHECK: bctrl
+; CHECK: ld 2, 40(1)
+; CHECK: blr
+}
+
+; Function Attrs: nounwind
+define void @ext() #0 {
+entry:
+  tail call void bitcast (%struct.cd* @extern_something to void ()*)() #0
+  ret void
+
+; CHECK-LABEL: @ext
+; CHECK-DAG: addis [[REG1:[0-9]+]], 2, [[NAME:[._A-Za-z0-9]+]]@toc@ha
+; CHECK-DAG: std 2, 40(1)
+; CHECK-DAG: ld [[REG3:[0-9]+]], [[NAME]]@toc@l(3)
+; CHECK-DAG: ld [[REG2:[0-9]+]], 0([[REG3]])
+; CHECK-DAG: ld 11, 16([[REG3]])
+; CHECK-DAG: ld 2, 8([[REG3]])
+; CHECK-DAG: mtctr [[REG2]]
+; CHECK: bctrl
+; CHECK: ld 2, 40(1)
+; CHECK: blr
+}
+
+attributes #0 = { nounwind }
+