Fix braino when handling branches fallthrough in arm backend.

bug: 62210114
Test: 657-branches

(cherry picked from commit 6fda42718a348cfb758d8714e223cab7e855765b)

Change-Id: I0e4f0577bcb1f3960459fe5d35473af191fc6534

3 files changed, 16 insertions, 9 deletions

diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index c9a6898e3b..419b2afe91 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -2522,21 +2522,28 @@ void InstructionCodeGeneratorARM::GenerateCompareTestAndBranch(HCondition* condi
   if (CanGenerateTest(condition, codegen_->GetAssembler())) {
     Label* non_fallthrough_target;
     bool invert;
+    bool emit_both_branches;
 
     if (true_target_in == nullptr) {
+      // The true target is fallthrough.
       DCHECK(false_target_in != nullptr);
       non_fallthrough_target = false_target_in;
       invert = true;
+      emit_both_branches = false;
     } else {
+      // Either the false target is fallthrough, or there is no fallthrough
+      // and both branches must be emitted.
       non_fallthrough_target = true_target_in;
       invert = false;
+      emit_both_branches = (false_target_in != nullptr);
     }
 
     const auto cond = GenerateTest(condition, invert, codegen_);
 
     __ b(non_fallthrough_target, cond.first);
 
-    if (false_target_in != nullptr && false_target_in != non_fallthrough_target) {
+    if (emit_both_branches) {
+      // No target falls through, we need to branch.
       __ b(false_target_in);
     }
 
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index fccb56786f..da146d72cd 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -3563,9 +3563,6 @@ void InstructionCodeGeneratorARM64::GenerateTestAndBranch(HInstruction* instruct
                                                           size_t condition_input_index,
                                                           vixl::aarch64::Label* true_target,
                                                           vixl::aarch64::Label* false_target) {
-  // FP branching requires both targets to be explicit. If either of the targets
-  // is nullptr (fallthrough) use and bind `fallthrough_target` instead.
-  vixl::aarch64::Label fallthrough_target;
   HInstruction* cond = instruction->InputAt(condition_input_index);
 
   if (true_target == nullptr && false_target == nullptr) {
@@ -3666,10 +3663,6 @@ void InstructionCodeGeneratorARM64::GenerateTestAndBranch(HInstruction* instruct
   if (true_target != nullptr && false_target != nullptr) {
     __ B(false_target);
   }
-
-  if (fallthrough_target.IsLinked()) {
-    __ Bind(&fallthrough_target);
-  }
 }
 
 void LocationsBuilderARM64::VisitIf(HIf* if_instr) {
diff --git a/compiler/optimizing/code_generator_arm_vixl.cc b/compiler/optimizing/code_generator_arm_vixl.cc
index 59cd5f951d..c37cc52a2b 100644
--- a/compiler/optimizing/code_generator_arm_vixl.cc
+++ b/compiler/optimizing/code_generator_arm_vixl.cc
@@ -2557,21 +2557,28 @@ void InstructionCodeGeneratorARMVIXL::GenerateCompareTestAndBranch(HCondition* c
   if (CanGenerateTest(condition, codegen_->GetAssembler())) {
     vixl32::Label* non_fallthrough_target;
     bool invert;
+    bool emit_both_branches;
 
     if (true_target_in == nullptr) {
+      // The true target is fallthrough.
       DCHECK(false_target_in != nullptr);
       non_fallthrough_target = false_target_in;
       invert = true;
+      emit_both_branches = false;
     } else {
       non_fallthrough_target = true_target_in;
       invert = false;
+      // Either the false target is fallthrough, or there is no fallthrough
+      // and both branches must be emitted.
+      emit_both_branches = (false_target_in != nullptr);
     }
 
     const auto cond = GenerateTest(condition, invert, codegen_);
 
     __ B(cond.first, non_fallthrough_target);
 
-    if (false_target_in != nullptr && false_target_in != non_fallthrough_target) {
+    if (emit_both_branches) {
+      // No target falls through, we need to branch.
       __ B(false_target_in);
     }