[GlobalISel] Accept multiple vregs for lowerCall's result

Change the interface of CallLowering::lowerCall to accept several
virtual registers for the call result, instead of just one.  This is a
follow-up to D46018.

CallLowering::lowerReturn was similarly refactored in D49660 and
lowerFormalArguments in D63549.

With this change, we no longer pack the virtual registers generated for
aggregates into one big lump before delegating to the target. Therefore,
the target can decide itself whether it wants to handle them as separate
pieces or use one big register.

ARM and AArch64 have been updated to use the passed in virtual registers
directly, which means we no longer need to generate so many
merge/extract instructions.

NFCI for AMDGPU, Mips and X86.

Differential Revision: https://reviews.llvm.org/D63550

llvm-svn: 364511

1 files changed, 3 insertions, 10 deletions

diff --git a/llvm/lib/Target/ARM/ARMCallLowering.cpp b/llvm/lib/Target/ARM/ARMCallLowering.cpp
index ea5bfb595a9..71b92517620 100644
--- a/llvm/lib/Target/ARM/ARMCallLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMCallLowering.cpp
@@ -619,21 +619,14 @@ bool ARMCallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
       return false;
 
     ArgInfos.clear();
-    SmallVector<Register, 8> SplitRegs;
-    splitToValueTypes(OrigRet, ArgInfos, MF,
-                      [&](Register Reg) { SplitRegs.push_back(Reg); });
+    splitToValueTypes(OrigRet, ArgInfos, MF, [&](Register Reg) {
+      llvm_unreachable("Call results should already be split");
+    });
 
     auto RetAssignFn = TLI.CCAssignFnForReturn(CallConv, IsVarArg);
     CallReturnHandler RetHandler(MIRBuilder, MRI, MIB, RetAssignFn);
     if (!handleAssignments(MIRBuilder, ArgInfos, RetHandler))
       return false;
-
-    if (!SplitRegs.empty()) {
-      // We have split the value and allocated each individual piece, now build
-      // it up again.
-      assert(OrigRet.Regs.size() == 1 && "Can't handle multple regs yet");
-      MIRBuilder.buildMerge(OrigRet.Regs[0], SplitRegs);
-    }
   }
 
   // We now know the size of the stack - update the ADJCALLSTACKDOWN