https://llvm.org/bugs/show_bug.cgi?id=23581
Bug ID: 23581
Summary: clang's -O implies -O2 whereas gcc's -O implies -O1
Product: clang
Version: 3.6
Hardware: PC
OS: FreeBSD
Status: NEW
Severity: normal
Priority: P
Component: Frontend
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
I've been tracking down issues with debuggability on FreeBSD. It turns out that
the -O with clang means -O2, not -O1 like it does with gcc. From man gcc for
4.8.3:
-O
-O1 Optimize. Optimizing compilation takes somewhat more time, and a
lot more memory for a large function.
With -O, the compiler tries to reduce code size and execution time,
without performing any optimizations that take a great deal of
compilation time.
-O turns on the following optimization flags:
-fauto-inc-dec -fcompare-elim -fcprop-registers -fdce -fdefer-pop
-fdelayed-branch -fdse -fguess-branch-probability -fif-conversion2
-fif-conversion -fipa-pure-const -fipa-profile -fipa-reference
-fmerge-constants -fsplit-wide-types -ftree-bit-ccp
-ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copyrename
-ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop
-ftree-fre -ftree-phiprop -ftree-slsr -ftree-sra -ftree-pta
-ftree-ter -funit-at-a-time
-O also turns on -fomit-frame-pointer on machines where doing so
does not interfere with debugging.
>From man clang for 3.6.0:
-O Equivalent to -O2.
-g Generate debug information. Note that Clang debug information
works best at -O0.
It seems counterintuitive for projects that have used gcc for over a decade to
change behavior in this way. Why was this done/shouldn't clang pattern itself
after gcc to some degree?
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
LLVMbugs mailing list
[email protected]
http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs
