SILGen KeyPath: Create a basic block to split the critical edge.

This is the one place in SILGen where we need to explicitly split the
critical edge. createBasicBlockAndBranch is a simply utility for that.

Author: atrick

lib/SILGen/SILGenExpr.cpp

@@ -3346,9 +3346,11 @@ getOrCreateKeyPathEqualsAndHash(SILGenModule &SGM,
         C.getBoolDecl()->getStoredProperties().front(), i1Ty);
 
       auto isTrueBB = subSGF.createBasicBlock();
-      
-      subSGF.B.createCondBranch(loc, isEqualI1, isTrueBB, isFalseBB);
-      
+      // Each false condition needs its own block to avoid critical edges.
+      auto falseEdgeBB = subSGF.createBasicBlockAndBranch(loc, isFalseBB);
+
+      subSGF.B.createCondBranch(loc, isEqualI1, isTrueBB, falseEdgeBB);
+
       subSGF.B.emitBlock(isTrueBB);
     }
 

lib/SILGen/SILGenStmt.cpp

@@ -79,6 +79,14 @@ SILBasicBlock *SILGenFunction::createBasicBlock(FunctionSection section) {
   llvm_unreachable("bad function section");
 }
 
+SILBasicBlock *
+SILGenFunction::createBasicBlockAndBranch(SILLocation loc,
+                                          SILBasicBlock *destBB) {
+  auto *newBB = createBasicBlock();
+  SILGenBuilder(B, newBB).createBranch(loc, destBB);
+  return newBB;
+}
+
 void SILGenFunction::eraseBasicBlock(SILBasicBlock *block) {
   assert(block->pred_empty() && "erasing block with predecessors");
   assert(block->empty() && "erasing block with content");