Fix late gc lowering issue

Author: gbaraldi

src/llvm-late-gc-lowering.cpp

@@ -1219,22 +1219,18 @@ State LateLowerGCFrame::LocalScan(Function &F) {
                                 else {
                                     Value *arg1 = (CI->arg_begin()[1])->stripInBoundsOffsets();
                                     SmallSetVector<AllocaInst *, 8>  gc_allocas = FindSretAllocas(arg1);
-                                    AllocaInst *SRet_gc = nullptr;
-                                    if (gc_allocas.size() == 1) {
-                                        SRet_gc = gc_allocas.pop_back_val();
+                                    if (gc_allocas.size() == 0) {
+                                        llvm_dump(CI);
+                                        assert(false && "Expected at least one alloca");
                                     }
                                     else {
-                                        llvm_dump(CI);
-                                        for (AllocaInst *Alloca : gc_allocas) {
-                                            llvm_dump(Alloca);
+                                        for (AllocaInst* SRet_gc : gc_allocas) {
+                                            Type *ElT = SRet_gc->getAllocatedType();
+                                            if (!(SRet_gc->isStaticAlloca() && isa<PointerType>(ElT) && ElT->getPointerAddressSpace() == AddressSpace::Tracked)) {
+                                                S.ArrayAllocas[SRet_gc] = tracked.count * cast<ConstantInt>(SRet_gc->getArraySize())->getZExtValue();
+                                            }
                                         }
-                                        assert(false && "Expected single alloca");
-                                    }
-                                    Type *ElT = SRet_gc->getAllocatedType();
-                                    if (!(SRet_gc->isStaticAlloca() && isa<PointerType>(ElT) && ElT->getPointerAddressSpace() == AddressSpace::Tracked)) {
-                                        S.ArrayAllocas[SRet_gc] = tracked.count * cast<ConstantInt>(SRet_gc->getArraySize())->getZExtValue();
                                     }
-                                    break; // Found our gc roots
                                 }
                             }
                         }

test/llvmpasses/late-lower-gc-sret.ll

@@ -47,3 +47,37 @@ ret:                                              ; preds = %false, %true
   ; CHECK: call void @julia.pop_gc_frame(ptr %gcframe)
   ret ptr addrspace(10) %1
 }
+
+declare swiftcc void @sret_call_gc(ptr noalias nocapture noundef sret({ ptr addrspace(10), i64, i64 }), ptr noalias nocapture noundef, ptr nonnull swiftself)
+
+declare ptr @julia.get_pgcstack()
+
+define hidden swiftcc void @sret_gc_root_phi(ptr nonnull swiftself %0, i1 %unpredictable) {
+top:
+  ; CHECK-LABEL: @sret_gc_root_phi
+  ; CHECK: %gcframe = call ptr @julia.new_gc_frame(i32 2)
+  ; CHECK: call ptr @julia.get_gc_frame_slot(ptr %gcframe, i32 1)
+  ; CHECK: call ptr @julia.get_gc_frame_slot(ptr %gcframe, i32 0)
+  ; CHECK: %pgcstack = call ptr @julia.get_pgcstack()
+  ; CHECK: call void @julia.push_gc_frame(ptr %gcframe, i32 2)
+  ; CHECK: alloca [3 x i64], align 8
+  %pgcstack = call ptr @julia.get_pgcstack()
+  %1 = alloca [3 x i64], align 8
+  %2 = alloca ptr addrspace(10), align 8
+  %3 = alloca ptr addrspace(10), align 8
+  store i64 0, ptr %2, align 8
+  store i64 0, ptr %3, align 8
+  br i1 %unpredictable, label %true, label %false
+
+true:                                             ; preds = %top
+  br label %ret
+
+false:                                            ; preds = %top
+  br label %ret
+
+ret:                                              ; preds = %false, %true
+  %4 = phi ptr [ %2, %true ], [ %3, %false ]
+  call swiftcc void @sret_call_gc(ptr noalias nocapture noundef sret({ ptr addrspace(10), i64, i64 }) %1, ptr noalias nocapture noundef %4, ptr nonnull swiftself %0)
+   ; CHECK: call void @julia.pop_gc_frame(ptr %gcframe)
+  ret void
+}