[MIPS GlobalISel] Lower SRet pointer arguments

[Petar.Avramovic]

Summary

Instead of returning structure by value clang usually adds pointer to
that structure as an argument. Pointers don't require special handling
no matter the SRet flag. Remove unsuccessful exit from lowerCall
for arguments with SRet flag if they are pointers.

[atanasyan]

LGTM

lib/Target/Mips/MipsCallLowering.cpp

bool MipsCallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
                                  CallLoweringInfo &Info) const {
 
   if (Info.CallConv != CallingConv::C)
     return false;
 
   for (auto &Arg : Info.OrigArgs) {
     if (!isSupportedType(Arg.Ty))
       return false;
-    if (Arg.Flags[0].isByVal() || Arg.Flags[0].isSRet())
+    if (Arg.Flags[0].isByVal())
+      return false;
+    if (Arg.Flags[0].isSRet() && !Arg.Ty->isPointerTy())
       return false;
   }
 
   if (!Info.OrigRet.Ty->isVoidTy() && !isSupportedType(Info.OrigRet.Ty))
     return false;
 
   MachineFunction &MF = MIRBuilder.getMF();
   const Function &F = MF.getFunction();

test/CodeGen/Mips/GlobalISel/irtranslator/sret_pointer.ll

+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+; RUN: llc -O0 -mtriple=mipsel-linux-gnu -global-isel -stop-after=irtranslator -verify-machineinstrs %s -o - | FileCheck %s -check-prefixes=MIPS32
+
+%struct.S = type { i32, i32 }
+
+define void @ZeroInit(%struct.S* noalias sret %agg.result) {
+  ; MIPS32-LABEL: name: ZeroInit
+  ; MIPS32: bb.1.entry:
+  ; MIPS32:   liveins: $a0
+  ; MIPS32:   [[COPY:%[0-9]+]]:_(p0) = COPY $a0
+  ; MIPS32:   [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+  ; MIPS32:   [[COPY1:%[0-9]+]]:_(p0) = COPY [[COPY]](p0)
+  ; MIPS32:   G_STORE [[C]](s32), [[COPY1]](p0) :: (store 4 into %ir.x)
+  ; MIPS32:   [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 4
+  ; MIPS32:   [[GEP:%[0-9]+]]:_(p0) = G_GEP [[COPY]], [[C1]](s32)
+  ; MIPS32:   G_STORE [[C]](s32), [[GEP]](p0) :: (store 4 into %ir.y)
+  ; MIPS32:   RetRA
+entry:
+  %x = getelementptr inbounds %struct.S, %struct.S* %agg.result, i32 0, i32 0
+  store i32 0, i32* %x, align 4
+  %y = getelementptr inbounds %struct.S, %struct.S* %agg.result, i32 0, i32 1
+  store i32 0, i32* %y, align 4
+  ret void
+}
+
+define void @CallZeroInit(%struct.S* noalias sret %agg.result) {
+  ; MIPS32-LABEL: name: CallZeroInit
+  ; MIPS32: bb.1.entry:
+  ; MIPS32:   liveins: $a0
+  ; MIPS32:   [[COPY:%[0-9]+]]:_(p0) = COPY $a0
+  ; MIPS32:   ADJCALLSTACKDOWN 16, 0, implicit-def $sp, implicit $sp
+  ; MIPS32:   $a0 = COPY [[COPY]](p0)
+  ; MIPS32:   JAL @ZeroInit, csr_o32, implicit-def $ra, implicit-def $sp, implicit $a0
+  ; MIPS32:   ADJCALLSTACKUP 16, 0, implicit-def $sp, implicit $sp
+  ; MIPS32:   RetRA
+entry:
+  call void @ZeroInit(%struct.S* sret %agg.result)
+  ret void
+}

test/CodeGen/Mips/GlobalISel/llvm-ir/sret_pointer.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc  -O0 -mtriple=mipsel-linux-gnu -global-isel  -verify-machineinstrs %s -o -| FileCheck %s -check-prefixes=MIPS32
+
+%struct.S = type { i32, i32 }
+
+define void @ZeroInit(%struct.S* noalias sret %agg.result) {
+; MIPS32-LABEL: ZeroInit:
+; MIPS32:       # %bb.0: # %entry
+; MIPS32-NEXT:    ori $1, $zero, 0
+; MIPS32-NEXT:    sw $1, 0($4)
+; MIPS32-NEXT:    sw $1, 4($4)
+; MIPS32-NEXT:    jr $ra
+; MIPS32-NEXT:    nop
+entry:
+  %x = getelementptr inbounds %struct.S, %struct.S* %agg.result, i32 0, i32 0
+  store i32 0, i32* %x, align 4
+  %y = getelementptr inbounds %struct.S, %struct.S* %agg.result, i32 0, i32 1
+  store i32 0, i32* %y, align 4
+  ret void
+}
+
+define void @CallZeroInit(%struct.S* noalias sret %agg.result) {
+; MIPS32-LABEL: CallZeroInit:
+; MIPS32:       # %bb.0: # %entry
+; MIPS32-NEXT:    addiu $sp, $sp, -24
+; MIPS32-NEXT:    .cfi_def_cfa_offset 24
+; MIPS32-NEXT:    sw $ra, 20($sp) # 4-byte Folded Spill
+; MIPS32-NEXT:    .cfi_offset 31, -4
+; MIPS32-NEXT:    jal ZeroInit
+; MIPS32-NEXT:    nop
+; MIPS32-NEXT:    lw $ra, 20($sp) # 4-byte Folded Reload
+; MIPS32-NEXT:    addiu $sp, $sp, 24
+; MIPS32-NEXT:    jr $ra
+; MIPS32-NEXT:    nop
+entry:
+  call void @ZeroInit(%struct.S* sret %agg.result)
+  ret void
+}