[Bug ipa/113293] Incorrect code after inlining function containing extended asm
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113293 --- Comment #4 from KBDeveloper --- (In reply to Alexander Monakov from comment #3) > (In reply to KBDeveloper from comment #2) > > > > Ah, that makes sense. I had assumed that taking the address of arg would > > force gcc to store it in memory somewhere. > > Is there a reason why gcc then allocates 8 bytes on the stack and fills r1 > > with sp - #7? Or is what I had just UB and gcc can do whatever? > > The compiler allocates stack memory for 'arg' and passes the address of > 'arg' to the asm; it is necessary in case the asm does something with it > without reading 'arg' itself. One example would be installing a hardware > watchpoint on that memory location. That makes sense. Thanks for the explanation (and your time!)
[Bug ipa/113293] Incorrect code after inlining function containing extended asm
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113293 Alexander Monakov changed: What|Removed |Added CC||amonakov at gcc dot gnu.org --- Comment #3 from Alexander Monakov --- (In reply to KBDeveloper from comment #2) > > Ah, that makes sense. I had assumed that taking the address of arg would > force gcc to store it in memory somewhere. > Is there a reason why gcc then allocates 8 bytes on the stack and fills r1 > with sp - #7? Or is what I had just UB and gcc can do whatever? The compiler allocates stack memory for 'arg' and passes the address of 'arg' to the asm; it is necessary in case the asm does something with it without reading 'arg' itself. One example would be installing a hardware watchpoint on that memory location.
[Bug ipa/113293] Incorrect code after inlining function containing extended asm
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113293 --- Comment #2 from KBDeveloper --- (In reply to Andrew Pinski from comment #1) > The inline-asm is not marking as clobbering memory. > > In this case since you just pass the address of the variable, gcc does not > know the inline-asm will read memory at all, it deletes the store. Anyways > adding "memory" as a clobber to the inline-asm, fixes the issue. Ah, that makes sense. I had assumed that taking the address of arg would force gcc to store it in memory somewhere. Is there a reason why gcc then allocates 8 bytes on the stack and fills r1 with sp - #7? Or is what I had just UB and gcc can do whatever? At any rate, thanks for the quick response.
[Bug ipa/113293] Incorrect code after inlining function containing extended asm
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113293 Andrew Pinski changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Keywords||inline-asm Resolution|--- |INVALID --- Comment #1 from Andrew Pinski --- The inline-asm is not marking as clobbering memory. In this case since you just pass the address of the variable, gcc does not know the inline-asm will read memory at all, it deletes the store. Anyways adding "memory" as a clobber to the inline-asm, fixes the issue.
