[CIR][FlattenCFG] Let results of CIR ScopeOp forwarded during FlattenCFG (#1147)

This PR implements NYI in CIRScopeOpFlattening. It seems to me the best
way is to let results of ScopeOp forwarded as block arguments of the
last block split from the cir.scope block.

Author: ghehg

clang/lib/CIR/Dialect/Transforms/FlattenCFG.cpp

@@ -135,13 +135,10 @@ class CIRScopeOpFlattening : public mlir::OpRewritePattern<cir::ScopeOp> {
     // Split the current block before the ScopeOp to create the inlining
     // point.
     auto *currentBlock = rewriter.getInsertionBlock();
-    auto *remainingOpsBlock =
+    mlir::Block *continueBlock =
         rewriter.splitBlock(currentBlock, rewriter.getInsertionPoint());
-    mlir::Block *continueBlock;
-    if (scopeOp.getNumResults() == 0)
-      continueBlock = remainingOpsBlock;
-    else
-      llvm_unreachable("NYI");
+    if (scopeOp.getNumResults() > 0)
+      continueBlock->addArguments(scopeOp.getResultTypes(), loc);
 
     // Inline body region.
     auto *beforeBody = &scopeOp.getRegion().front();

clang/test/CIR/CodeGen/fullexpr.cpp

@@ -1,5 +1,10 @@
 // RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
 // RUN: FileCheck --input-file=%t.cir %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir-flat %s -o %t.cir.flat
+// RUN: FileCheck --check-prefix=FLAT  --input-file=%t.cir.flat %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm -o - %s \
+// RUN: | opt -S -passes=instcombine,mem2reg,simplifycfg -o %t.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t.ll %s
 
 int go(int const& val);
 
@@ -18,3 +23,31 @@ int go1() {
 // CHECK-NEXT:   cir.yield %[[#RValTmp]] : !s32i
 // CHECK-NEXT: }
 // CHECK-NEXT: cir.store %[[#RVal]], %[[#XAddr]] : !s32i, !cir.ptr<!s32i>
+
+// FLAT: cir.func @_Z3go1v() -> !s32i
+// FLAT: %[[#TmpAddr:]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["ref.tmp0", init] {alignment = 4 : i64}
+// FLAT: %[[#XAddr:]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init] {alignment = 4 : i64}
+// FLAT: cir.br ^[[before_body:.*]]{{ loc.*}}
+// FLAT-NEXT: ^[[before_body]]:  // pred: ^bb0
+// FLAT-NEXT:   %[[#One:]] = cir.const #cir.int<1> : !s32i
+// FLAT-NEXT:   cir.store %[[#One]], %[[#TmpAddr]] : !s32i, !cir.ptr<!s32i>
+// FLAT-NEXT:   %[[#RValTmp:]] = cir.call @_Z2goRKi(%[[#TmpAddr]]) : (!cir.ptr<!s32i>) -> !s32i
+// FLAT-NEXT:   cir.br ^[[continue_block:.*]](%[[#RValTmp]] : !s32i) {{loc.*}}
+// FLAT-NEXT: ^[[continue_block]](%[[#BlkArgRval:]]: !s32i {{loc.*}}):  // pred: ^[[before_body]]
+// FLAT-NEXT:   cir.store %[[#BlkArgRval]], %[[#XAddr]] : !s32i, !cir.ptr<!s32i>
+
+// LLVM-LABEL: @_Z3go1v()
+// LLVM-NEXT: %[[#TmpAddr:]] = alloca i32, i64 1, align 4
+// LLVM: br label %[[before_body:[0-9]+]]
+// LLVM: [[before_body]]:
+// LLVM-NEXT: store i32 1, ptr %[[#TmpAddr]], align 4
+// LLVM-NEXT: %[[#RValTmp:]] = call i32 @_Z2goRKi(ptr %[[#TmpAddr]])
+// LLVM-NEXT: br label %[[continue_block:[0-9]+]] 
+
+// LLVM: [[continue_block]]:
+// LLVM-NEXT: [[PHI:%.*]] = phi i32 [ %[[#RValTmp]], %[[before_body]] ]
+// LLVM: store i32 [[PHI]], ptr [[TMP0:%.*]], align 4
+// LLVM: [[TMP1:%.*]] = load i32, ptr [[TMP0]], align 4
+// LLVM: store i32 [[TMP1]], ptr [[TMP2:%.*]], align 4
+// LLVM: [[TMP3:%.*]] = load i32, ptr [[TMP2]], align 4
+// LLVM: ret i32 [[TMP3]]