[arm] Do not emit the constant pool before a branch

backes · V8 LUCI CQ · commit 9be597d194e1 · 2022-12-14T06:45:53.000Z
After computing the branch offset but before emitting the actual branch, we should not emit a constant pool. Otherwise the previously computed offset would be off. Instead of handling this indirectly via the Assembler::branch_offset method, do this directly in the Assembler::b method (and friends), so it is not missed on other call sites. R=jkummerow@chromium.org Bug: chromium:1399424 Change-Id: I0cbb219ced5b671001a296b1cc7c339f395abffe Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4102800 Commit-Queue: Clemens Backes <clemensb@chromium.org> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org> Cr-Commit-Position: refs/heads/main@{#84828}
diff --git a/src/codegen/arm/assembler-arm.cc b/src/codegen/arm/assembler-arm.cc
@@ -1444,10 +1444,6 @@ int Assembler::branch_offset(Label* L) {
     L->link_to(pc_offset());
   }
 
-  // Block the emission of the constant pool, since the branch instruction must
-  // be emitted at the pc offset recorded by the label.
-  if (!is_const_pool_blocked()) BlockConstPoolFor(1);
-
   return target_pos - (pc_offset() + Instruction::kPcLoadDelta);
 }
 
@@ -1458,6 +1454,11 @@ void Assembler::b(int branch_offset, Condition cond, RelocInfo::Mode rmode) {
   int imm24 = branch_offset >> 2;
   const bool b_imm_check = is_int24(imm24);
   CHECK(b_imm_check);
+
+  // Block the emission of the constant pool before the next instruction.
+  // Otherwise the passed-in branch offset would be off.
+  BlockConstPoolFor(1);
+
   emit(cond | B27 | B25 | (imm24 & kImm24Mask));
 
   if (cond == al) {
@@ -1472,6 +1473,11 @@ void Assembler::bl(int branch_offset, Condition cond, RelocInfo::Mode rmode) {
   int imm24 = branch_offset >> 2;
   const bool bl_imm_check = is_int24(imm24);
   CHECK(bl_imm_check);
+
+  // Block the emission of the constant pool before the next instruction.
+  // Otherwise the passed-in branch offset would be off.
+  BlockConstPoolFor(1);
+
   emit(cond | B27 | B25 | B24 | (imm24 & kImm24Mask));
 }
 
@@ -1481,6 +1487,11 @@ void Assembler::blx(int branch_offset) {
   int imm24 = branch_offset >> 2;
   const bool blx_imm_check = is_int24(imm24);
   CHECK(blx_imm_check);
+
+  // Block the emission of the constant pool before the next instruction.
+  // Otherwise the passed-in branch offset would be off.
+  BlockConstPoolFor(1);
+
   emit(kSpecialCondition | B27 | B25 | h | (imm24 & kImm24Mask));
 }
 
