[NVPTX] Allow libcalls that are defined in the current module.

The patch adds a possibility to make library calls on NVPTX.

An important thing about library functions - they must be defined within
the current module. This basically should guarantee that we produce a
valid PTX assembly (without calls to not defined functions). The one who
wants to use the libcalls is probably will have to link against
compiler-rt or any other implementation.

Currently, it's completely impossible to make library calls because of
error LLVM ERROR: Cannot select: i32 = ExternalSymbol '...'. But we can
lower ExternalSymbol to TargetExternalSymbol and verify if the function
definition is available.

Also, there was an issue with a DAG during legalisation. When we expand
instruction into libcall, the inner call-chain isn't being "integrated"
into outer chain. Since the last "data-flow" (call retval load) node is
located in call-chain earlier than CALLSEQ_END node, the latter becomes
a leaf and therefore a dead node (and is being removed quite fast).
Proposed here solution relies on another data-flow pseudo nodes
(ProxyReg) which purpose is only to keep CALLSEQ_END at legalisation and
instruction selection phases - we remove the pseudo instructions before
register scheduling phase.

Patch by Denys Zariaiev!

Differential Revision: https://reviews.llvm.org/D34708

llvm-svn: 350069

1 files changed, 31 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/NVPTX/libcall-fulfilled.ll b/llvm/test/CodeGen/NVPTX/libcall-fulfilled.ll
new file mode 100644
index 00000000000..9d6777d59c3
--- /dev/null
+++ b/llvm/test/CodeGen/NVPTX/libcall-fulfilled.ll
@@ -0,0 +1,31 @@
+; RUN: llc < %s -march=nvptx 2>&1 | FileCheck %s
+; Allow to make libcalls that are defined in the current module
+
+; Underlying libcall declaration
+; CHECK: .visible .func  (.param .align 16 .b8 func_retval0[16]) __umodti3
+
+define i128 @remainder(i128, i128) {
+bb0:
+  ; CHECK:      { // callseq 0, 0
+  ; CHECK:      call.uni (retval0),
+  ; CHECK-NEXT: __umodti3,
+  ; CHECK-NEXT: (
+  ; CHECK-NEXT: param0,
+  ; CHECK-NEXT: param1
+  ; CHECK-NEXT: );
+  ; CHECK-NEXT: ld.param.v2.b64 {%[[REG0:rd[0-9]+]], %[[REG1:rd[0-9]+]]}, [retval0+0];
+  ; CHECK-NEXT: } // callseq 0
+  %a = urem i128 %0, %1
+  br label %bb1
+
+bb1:
+  ; CHECK-NEXT: st.param.v2.b64 [func_retval0+0], {%[[REG0]], %[[REG1]]};
+  ; CHECK-NEXT: ret;
+  ret i128 %a
+}
+
+; Underlying libcall definition
+; CHECK: .visible .func  (.param .align 16 .b8 func_retval0[16]) __umodti3(
+define i128 @__umodti3(i128, i128) {
+  ret i128 0
+}