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Unified Diff: src/compiler/ia32/instruction-selector-ia32.cc

Issue 931623002: [turbofan] Optimize certain chains of Branch into a Switch. (Closed) Base URL: https://chromium.googlesource.com/v8/v8.git@master
Patch Set: Addrssed comments. Created 5 years, 10 months ago
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Index: src/compiler/ia32/instruction-selector-ia32.cc
diff --git a/src/compiler/ia32/instruction-selector-ia32.cc b/src/compiler/ia32/instruction-selector-ia32.cc
index da2a6594196951d33fd196a3070bda2b7958695f..beec701903ec4598f26fb3d093b7898b2ea27804 100644
--- a/src/compiler/ia32/instruction-selector-ia32.cc
+++ b/src/compiler/ia32/instruction-selector-ia32.cc
@@ -928,6 +928,67 @@ void InstructionSelector::VisitBranch(Node* branch, BasicBlock* tbranch,
}
+void InstructionSelector::VisitSwitch(Node* node, BasicBlock* default_branch,
+ BasicBlock** case_branches,
+ int32_t* case_values, size_t case_count,
+ int32_t min_value, int32_t max_value) {
+ IA32OperandGenerator g(this);
+ InstructionOperand value_operand = g.UseRegister(node->InputAt(0));
+ InstructionOperand default_operand = g.Label(default_branch);
+
+ // Note that {value_range} can be 0 if {min_value} is -2^31 and {max_value}
+ // is 2^31-1, so don't assume that it's non-zero below.
+ size_t value_range =
+ 1u + bit_cast<uint32_t>(max_value) - bit_cast<uint32_t>(min_value);
+
+ // Determine whether to issue an ArchTableSwitch or an ArchLookupSwitch
+ // instruction.
+ size_t table_space_cost = 4 + value_range;
+ size_t table_time_cost = 3;
+ size_t lookup_space_cost = 3 + 2 * case_count;
+ size_t lookup_time_cost = case_count;
+ if (case_count > 4 &&
+ table_space_cost + 3 * table_time_cost <=
+ lookup_space_cost + 3 * lookup_time_cost &&
+ min_value > std::numeric_limits<int32_t>::min()) {
+ InstructionOperand index_operand = value_operand;
+ if (min_value) {
+ index_operand = g.TempRegister();
+ Emit(kIA32Lea | AddressingModeField::encode(kMode_MRI), index_operand,
+ value_operand, g.TempImmediate(-min_value));
+ }
+ size_t input_count = 2 + value_range;
+ auto* inputs = zone()->NewArray<InstructionOperand>(input_count);
+ inputs[0] = index_operand;
+ std::fill(&inputs[1], &inputs[input_count], default_operand);
+ for (size_t index = 0; index < case_count; ++index) {
+ size_t value = case_values[index] - min_value;
+ BasicBlock* branch = case_branches[index];
+ DCHECK_LE(0u, value);
+ DCHECK_LT(value + 2, input_count);
+ inputs[value + 2] = g.Label(branch);
+ }
+ Emit(kArchTableSwitch, 0, nullptr, input_count, inputs, 0, nullptr)
+ ->MarkAsControl();
+ return;
+ }
+
+ // Generate a sequence of conditional jumps.
+ size_t input_count = 2 + case_count * 2;
+ auto* inputs = zone()->NewArray<InstructionOperand>(input_count);
+ inputs[0] = value_operand;
+ inputs[1] = default_operand;
+ for (size_t index = 0; index < case_count; ++index) {
+ int32_t value = case_values[index];
+ BasicBlock* branch = case_branches[index];
+ inputs[index * 2 + 2 + 0] = g.TempImmediate(value);
+ inputs[index * 2 + 2 + 1] = g.Label(branch);
+ }
+ Emit(kArchLookupSwitch, 0, nullptr, input_count, inputs, 0, nullptr)
+ ->MarkAsControl();
+}
+
+
void InstructionSelector::VisitWord32Equal(Node* const node) {
FlagsContinuation cont(kEqual, node);
Int32BinopMatcher m(node);
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