From cb5cb74461ac9407c16903bfa9d2855f4e76918e Mon Sep 17 00:00:00 2001 From: Pierre Ducroquet Date: Wed, 7 Jan 2026 15:43:19 +0100 Subject: [PATCH] llvmjit: always use the simplifycfg pass The simplifycfg pass will remove empty or unreachable LLVM basic blocks, and merge blocks together when possible. This is important because the tuple deforming code will generate a lot of basic blocks, and previously with O0 we did not run this pass, thus creating this kind of (amd64) machine code: 0x723382b781c1: jmp 0x723382b781c3 0x723382b781c3: jmp 0x723382b781eb 0x723382b781c5: mov -0x20(%rsp),%rax 0x723382b781..: ... ..... 0x723382b781e7: mov %cx,(%rax) 0x723382b781ea: ret 0x723382b781eb: jmp 0x723382b781ed 0x723382b781ed: jmp 0x723382b781ef 0x723382b781ef: jmp 0x723382b781f1 0x723382b781f1: jmp 0x723382b781f3 0x723382b781f3: mov -0x30(%rsp),%rax 0x723382b781..: ... ...... 0x723382b78208: mov %rcx,(%rax) 0x723382b7820b: jmp 0x723382b781c5 This is not efficient at all, and triggering the simplifycfg pass ends up tacking a few hundreds micro seconds while possibly saving much more time during execution. On a basic benchmark, I saved 7ms on query runtime while using 0.2ms on extra JIT compilation overhead --- src/backend/jit/llvm/llvmjit.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/src/backend/jit/llvm/llvmjit.c b/src/backend/jit/llvm/llvmjit.c index 2e8aa4749db..c22f83e97cf 100644 --- a/src/backend/jit/llvm/llvmjit.c +++ b/src/backend/jit/llvm/llvmjit.c @@ -633,6 +633,11 @@ llvm_optimize_module(LLVMJitContext *context, LLVMModuleRef module) { /* we rely on mem2reg heavily, so emit even in the O0 case */ LLVMAddPromoteMemoryToRegisterPass(llvm_fpm); + /* + * the tuple deforming generates a lot of basic blocks, + * simplify them even with O0 + */ + LLVMAddCFGSimplificationPass(llvm_fpm); } LLVMPassManagerBuilderPopulateFunctionPassManager(llvm_pmb, llvm_fpm); @@ -676,10 +681,10 @@ llvm_optimize_module(LLVMJitContext *context, LLVMModuleRef module) passes = "default"; else if (context->base.flags & PGJIT_INLINE) /* if doing inlining, but no expensive optimization, add inline pass */ - passes = "default,mem2reg,inline"; + passes = "default,mem2reg,simplifycfg,inline"; else /* default includes always-inline pass */ - passes = "default,mem2reg"; + passes = "default,mem2reg,simplifycfg"; options = LLVMCreatePassBuilderOptions(); -- 2.43.0