IRGen: Hint condfail branches.

Mark the condfail condition as expected-false, and arrange the generated code so that the trap
basic block is emitted out-of-line, and the happy path falls through.

Author: jckarter

lib/IRGen/IRGenSIL.cpp

@@ -5466,11 +5466,19 @@ void IRGenSILFunction::visitCondFailInst(swift::CondFailInst *i) {
   Explosion e = getLoweredExplosion(i->getOperand());
   llvm::Value *cond = e.claimNext();
 
+  // The condition should be false, or we die.
+  auto expectedCond = Builder.CreateExpect(cond,
+                                         llvm::ConstantInt::get(IGM.Int1Ty, 0));
+  
   // Emit individual fail blocks so that we can map the failure back to a source
   // line.
+  auto origInsertionPoint = Builder.GetInsertBlock();
+
   llvm::BasicBlock *failBB = llvm::BasicBlock::Create(IGM.getLLVMContext());
   llvm::BasicBlock *contBB = llvm::BasicBlock::Create(IGM.getLLVMContext());
-  Builder.CreateCondBr(cond, failBB, contBB);
+  Builder.CreateCondBr(expectedCond, failBB, contBB);
+    
+  Builder.SetInsertPoint(&CurFn->back());
   Builder.emitBlock(failBB);
   if (IGM.DebugInfo)
     // If we are emitting DWARF, this does nothing. Otherwise the ``llvm.trap``
@@ -5479,6 +5487,8 @@ void IRGenSILFunction::visitCondFailInst(swift::CondFailInst *i) {
     // in CodeView.
     IGM.DebugInfo->setInlinedTrapLocation(Builder, i->getDebugScope());
   emitTrap(i->getMessage(), /*EmitUnreachable=*/true);
+  
+  Builder.SetInsertPoint(origInsertionPoint);
   Builder.emitBlock(contBB);
   FailBBs.push_back(failBB);
 }

test/IRGen/builtins.swift

@@ -314,10 +314,12 @@ func testStaticReport(_ b: Bool, ptr: Builtin.RawPointer) -> () {
 
 // CHECK-LABEL: define hidden {{.*}}void @"$s8builtins12testCondFail{{[_0-9a-zA-Z]*}}F"(i1, i1)
 func testCondFail(_ b: Bool, c: Bool) {
-  // CHECK: br i1 %0, label %[[FAIL:.*]], label %[[CONT:.*]]
+  // CHECK: [[EXPECT:%.*]] = call i1 @llvm.expect.i1(i1 %0, i1 false)
+  // CHECK: br i1 [[EXPECT]], label %[[FAIL:.*]], label %[[CONT:.*]]
   Builtin.condfail_message(b, StaticString("message").unsafeRawPointer)
   // CHECK: [[CONT]]
-  // CHECK: br i1 %1, label %[[FAIL2:.*]], label %[[CONT:.*]]
+  // CHECK: [[EXPECT:%.*]] = call i1 @llvm.expect.i1(i1 %1, i1 false)
+  // CHECK: br i1 [[EXPECT]], label %[[FAIL2:.*]], label %[[CONT:.*]]
   Builtin.condfail_message(c, StaticString("message").unsafeRawPointer)
   // CHECK: [[CONT]]
   // CHECK: ret void