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@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@plt”
4 retq
5 #NO_APP
BR!
Thank you!
Xiang