[llvm-dev] [x86][inline-asm] Generate call instruction in pic (original) (raw)
Zhang, Xiang1 via llvm-dev llvm-dev at lists.llvm.org
Fri Aug 13 03:24:32 PDT 2021
- Previous message: [llvm-dev] Unreachable CFG subcomponent produced by jump threading
- Next message: [llvm-dev] llvm intrinsics
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
We encounter a inline bug in generating call, hard to fix. I want to ask some questions here.
1st Does the IR generate from FE is wrong ? PLS refer t.ll line3, it use "m" constrain for call operand "void (...) @sincos". I think the right IR should be ("m" + "void (...)* @sincos") or ("m" + "void (...)* @sincos_ptr") related patch in FE https://reviews.llvm.org/D107523
2nd How we fix it in Back End ? I find it is hard to fix in BE, because the current arch of inline_asm let us hard to match the variable to its instruction. I create a unbeautiful patch at BE too https://reviews.llvm.org/D108024
The following code will generate one more time load for "sincos" with cmd "clang -fasm-blocks t.c -fpic -S -emit-llvm" + "llc t.ll" t.c: 1 extern void sincos (); 2 void foo (){ 3 __asm{ 4 call sincos 5 ret }; 6 }
t.ll:
1 define void @foo() #0 {
2 entry:
3 call void asm sideeffect inteldialect "call qword ptr ${0:P}\0A\09ret", "m,{dirflag},{fpsr},~{flags}"(void (...) @sincos) #2, !srcloc !5
4 ret void
5 }
t.s:
1 movq sincos at GOTPCREL(%rip), %rax // now the rax has been the function address "sincos"
2 #APP
3 callq *(%rax) // the call should directly read the %rax, should not "load" it again, it should be "callq *%rax" or better code "call sincos at plt"
4 retq
5 #NO_APP
BR! Thank you! Xiang
-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210813/3abc3839/attachment.html>
- Previous message: [llvm-dev] Unreachable CFG subcomponent produced by jump threading
- Next message: [llvm-dev] llvm intrinsics
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]