[CIR][CodeGen] Emit cir.resume for synthetic TryOp's in place #1418

bruteforceboy · 2025-02-27T12:09:05Z

Currently, the following code snippet fails during CIR codegen with exceptions enabled:

#include <string>

void foo(const char *path) {
  std::string str = path;
  str = path;
  str = path;
}

using bin/clang++ tmp.cpp -fclangir -Xclang -emit-cir -S, the error:

error: empty block: expect at least a terminator

Relevant part of the CIR before verification looks like:

%118 = "cir.load"(%114) : (!cir.ptr<!cir.ptr<!cir.int<s, 8>>>) -> !cir.ptr<!cir.int<s, 8>>
"cir.try"() <{catch_types = [#cir.unwind], cleanup, synthetic}> ({
    %123 = "cir.call"(%115, %118) <{ast = #cir.call.expr.ast, callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEaSEPKc, calling_conv = 1 : i32, exception, extra_attrs = #cir<extra({})>, side_effect = 1 : i32}> ({
    "cir.call"(%115) <{callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEED1Ev, calling_conv = 1 : i32, extra_attrs = #cir<extra({nothrow = #cir.nothrow})>, side_effect = 1 : i32}> ({
    }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>) -> ()
    "cir.yield"() : () -> ()
    }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.int<s, 8>>) -> !cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>
    "cir.store"(%123, %116) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>>) -> ()
    "cir.yield"() : () -> ()
}, {
^bb0:              <--- EMPTY BLOCK
}) : () -> ()

There is an empty block! If you extend the snippet with more str = path;, you get more empty blocks...

The issue is the cir.resume ops which should be in those empty blocks from synthetic TryOp's aren't linked properly during the cleanup.

My suggestion: We should explicitly add cir.resume for synthetic tryOp's, because we already know they have just an unwind handler. So, during CIRGenCleanup we don't need to add cir.resume for synthetic TryOp's. This PR adds this and a test.

bcardosolopes

Awesome, elegant fix! One minor nit below

clang/test/CIR/CodeGen/string.cpp

Currently, the following code snippet fails during CIR codegen with exceptions enabled: ``` #include <string> void foo(const char *path) { std::string str = path; str = path; str = path; } ``` using `bin/clang++ tmp.cpp -fclangir -Xclang -emit-cir -S`, the error: ``` error: empty block: expect at least a terminator ``` Relevant part of the CIR before verification looks like: ``` %118 = "cir.load"(%114) : (!cir.ptr<!cir.ptr<!cir.int<s, 8>>>) -> !cir.ptr<!cir.int<s, 8>> "cir.try"() <{catch_types = [#cir.unwind], cleanup, synthetic}> ({ %123 = "cir.call"(%115, %118) <{ast = #cir.call.expr.ast, callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEaSEPKc, calling_conv = 1 : i32, exception, extra_attrs = #cir<extra({})>, side_effect = 1 : i32}> ({ "cir.call"(%115) <{callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEED1Ev, calling_conv = 1 : i32, extra_attrs = #cir<extra({nothrow = #cir.nothrow})>, side_effect = 1 : i32}> ({ }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>) -> () "cir.yield"() : () -> () }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.int<s, 8>>) -> !cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>> "cir.store"(%123, %116) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>>) -> () "cir.yield"() : () -> () }, { ^bb0: <--- EMPTY BLOCK }) : () -> () ``` There is an empty block! If you extend the snippet with more `str = path;`, you get more empty blocks... The issue is the `cir.resume` ops which should be in those empty blocks from synthetic TryOp's aren't linked properly during the cleanup. My suggestion: We should explicitly add `cir.resume` for synthetic tryOp's, because we already know they have just an [unwind handler](https://github.com/llvm/clangir/blob/8746bd4bbe777352c2935e9937449637a8943767/clang/lib/CIR/CodeGen/CIRGenCall.cpp#L506). So, during [CIRGenCleanup](https://github.com/llvm/clangir/blob/8746bd4bbe777352c2935e9937449637a8943767/clang/lib/CIR/CodeGen/CIRGenCleanup.cpp#L667) we don't need to add `cir.resume` for synthetic TryOp's. This PR adds this and a test.

) Currently, the following code snippet fails during CIR codegen with exceptions enabled: ``` #include <string> void foo(const char *path) { std::string str = path; str = path; str = path; } ``` using `bin/clang++ tmp.cpp -fclangir -Xclang -emit-cir -S`, the error: ``` error: empty block: expect at least a terminator ``` Relevant part of the CIR before verification looks like: ``` %118 = "cir.load"(%114) : (!cir.ptr<!cir.ptr<!cir.int<s, 8>>>) -> !cir.ptr<!cir.int<s, 8>> "cir.try"() <{catch_types = [#cir.unwind], cleanup, synthetic}> ({ %123 = "cir.call"(%115, %118) <{ast = #cir.call.expr.ast, callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEaSEPKc, calling_conv = 1 : i32, exception, extra_attrs = #cir<extra({})>, side_effect = 1 : i32}> ({ "cir.call"(%115) <{callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEED1Ev, calling_conv = 1 : i32, extra_attrs = #cir<extra({nothrow = #cir.nothrow})>, side_effect = 1 : i32}> ({ }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>) -> () "cir.yield"() : () -> () }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.int<s, 8>>) -> !cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>> "cir.store"(%123, %116) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>>) -> () "cir.yield"() : () -> () }, { ^bb0: <--- EMPTY BLOCK }) : () -> () ``` There is an empty block! If you extend the snippet with more `str = path;`, you get more empty blocks... The issue is the `cir.resume` ops which should be in those empty blocks from synthetic TryOp's aren't linked properly during the cleanup. My suggestion: We should explicitly add `cir.resume` for synthetic tryOp's, because we already know they have just an [unwind handler](https://github.com/llvm/clangir/blob/8746bd4bbe777352c2935e9937449637a8943767/clang/lib/CIR/CodeGen/CIRGenCall.cpp#L506). So, during [CIRGenCleanup](https://github.com/llvm/clangir/blob/8746bd4bbe777352c2935e9937449637a8943767/clang/lib/CIR/CodeGen/CIRGenCleanup.cpp#L667) we don't need to add `cir.resume` for synthetic TryOp's. This PR adds this and a test.

bruteforceboy added 2 commits February 27, 2025 13:46

add synthetic fix

796f930

update test

cd8969e

bruteforceboy requested review from bcardosolopes and lanza as code owners February 27, 2025 12:09

bcardosolopes requested changes Feb 27, 2025

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clang/test/CIR/CodeGen/string.cpp Outdated Show resolved Hide resolved

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bcardosolopes approved these changes Mar 1, 2025

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bcardosolopes merged commit d2209ec into llvm:main Mar 1, 2025
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[CIR][CodeGen] Emit cir.resume for synthetic TryOp's in place #1418

[CIR][CodeGen] Emit cir.resume for synthetic TryOp's in place #1418

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[CIR][CodeGen] Emit cir.resume for synthetic TryOp's in place #1418

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