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Manually short circuit in lb_build_if_stmt for constant conditions

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gingerBill
2021-07-26 10:59:07 +01:00
parent 3ac674cf02
commit 08dc829b70
1 changed files with 52 additions and 10 deletions
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62
src/llvm_backend.cpp
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@@ -5486,6 +5486,7 @@ void lb_build_return_stmt(lbProcedure *p, Slice<Ast *> const &return_results) {
void lb_build_if_stmt(lbProcedure *p, Ast *node) {
ast_node(is, IfStmt, node);
lb_open_scope(p, node->scope); // Scope #1
defer (lb_close_scope(p, lbDeferExit_Default, nullptr));
if (is->init != nullptr) {
// TODO(bill): Should this have a separate block to begin with?
@@ -5503,30 +5504,67 @@ void lb_build_if_stmt(lbProcedure *p, Ast *node) {
else_ = lb_create_block(p, "if.else");
}
lb_build_cond(p, is->cond, then, else_);
lb_start_block(p, then);
lbValue cond = lb_build_cond(p, is->cond, then, else_);
if (is->label != nullptr) {
lbTargetList *tl = lb_push_target_list(p, is->label, done, nullptr, nullptr);
tl->is_block = true;
}
lb_build_stmt(p, is->body);
if (LLVMIsConstant(cond.value)) {
// NOTE(bill): Do a compile time short circuit for when the condition is constantly known.
// This done manually rather than relying on the SSA passes because sometimes the SSA passes
// miss some even if they are constantly known, especially with few optimization passes.
lb_emit_jump(p, done);
bool const_cond = LLVMConstIntGetZExtValue(cond.value) != 0;
if (is->else_stmt != nullptr) {
lb_start_block(p, else_);
LLVMValueRef if_instr = LLVMGetLastInstruction(p->curr_block->block);
GB_ASSERT(LLVMGetInstructionOpcode(if_instr) == LLVMBr);
GB_ASSERT(LLVMIsConditional(if_instr));
LLVMInstructionEraseFromParent(if_instr);
lb_open_scope(p, is->else_stmt->scope);
lb_build_stmt(p, is->else_stmt);
lb_close_scope(p, lbDeferExit_Default, nullptr);
if (const_cond) {
lb_emit_jump(p, then);
lb_start_block(p, then);
lb_build_stmt(p, is->body);
lb_emit_jump(p, done);
} else {
if (is->else_stmt != nullptr) {
lb_emit_jump(p, else_);
lb_start_block(p, else_);
lb_open_scope(p, is->else_stmt->scope);
lb_build_stmt(p, is->else_stmt);
lb_close_scope(p, lbDeferExit_Default, nullptr);
}
lb_emit_jump(p, done);
}
} else {
lb_start_block(p, then);
lb_build_stmt(p, is->body);
lb_emit_jump(p, done);
if (is->else_stmt != nullptr) {
lb_start_block(p, else_);
lb_open_scope(p, is->else_stmt->scope);
lb_build_stmt(p, is->else_stmt);
lb_close_scope(p, lbDeferExit_Default, nullptr);
lb_emit_jump(p, done);
}
}
if (is->label != nullptr) {
lb_pop_target_list(p);
}
lb_start_block(p, done);
lb_close_scope(p, lbDeferExit_Default, nullptr);
}
void lb_build_for_stmt(lbProcedure *p, Ast *node) {
@@ -5842,6 +5880,10 @@ void lb_build_stmt(lbProcedure *p, Ast *node) {
lb_emit_jump(p, done);
lb_start_block(p, done);
}
if (bs->label != nullptr) {
lb_pop_target_list(p);
}
case_end;
case_ast_node(vd, ValueDecl, node);