[compiler] Support non-branch continuations for StackPointerGreaterThan

We previously had a DCHECK to protect the assumption that the
continuation to StackPointerGreaterThan must be a branch. This is not
a valid assumption to make, in fact the second callsite of
VisitStackPointerGreaterThan immediately violates it.

Instead, this CL additionally considers non-branch continuations when
getting the effect level.

A slight digression since it was not clear to me how comparison
results were materialized for 'Set' continuations: this happens during
codegen, where CodeGenerator::AssembleInstruction inserts a call to
AssembleArchBoolean if necessary.

Bug: v8:9829,v8:9534
Change-Id: Ib554071b7aa33e0f6b8a0d605219db6b6dc7d5b0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1871912Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64430}

src/compiler/backend/ia32/instruction-selector-ia32.cc

@@ -580,9 +580,11 @@ void InstructionSelector::VisitStackPointerGreaterThan(
   Node* const value = node->InputAt(0);
   InstructionCode opcode = kArchStackPointerGreaterThan;
 
-  DCHECK(cont->IsBranch());
-  const int effect_level =
-      GetEffectLevel(cont->true_block()->PredecessorAt(0)->control_input());
+  int effect_level = GetEffectLevel(node);
+  if (cont->IsBranch()) {
+    effect_level =
+        GetEffectLevel(cont->true_block()->PredecessorAt(0)->control_input());
+  }
 
   IA32OperandGenerator g(this);
   if (g.CanBeMemoryOperand(kIA32Cmp, node, value, effect_level)) {

src/compiler/backend/x64/instruction-selector-x64.cc

@@ -548,9 +548,11 @@ void InstructionSelector::VisitStackPointerGreaterThan(
   Node* const value = node->InputAt(0);
   InstructionCode opcode = kArchStackPointerGreaterThan;
 
-  DCHECK(cont->IsBranch());
-  const int effect_level =
-      GetEffectLevel(cont->true_block()->PredecessorAt(0)->control_input());
+  int effect_level = GetEffectLevel(node);
+  if (cont->IsBranch()) {
+    effect_level =
+        GetEffectLevel(cont->true_block()->PredecessorAt(0)->control_input());
+  }
 
   X64OperandGenerator g(this);
   if (g.CanBeMemoryOperand(kX64Cmp, node, value, effect_level)) {