On Fri, Oct 07, 2022 at 01:32:36PM -0700, Nick Desaulniers wrote:
> When debugging LLVM IR, it can be handy for clang to not discard value
> names used for local variables and parameters. Compare the generated IR.
>
> Implicit Default (-fdiscard-value-names):
> define i32 @core_sys_select(i32 %0, ptr %1, ptr %2, ptr %3, ptr %4) {
> %6 = alloca i64
> %7 = alloca %struct.poll_wqueues
> %8 = alloca [64 x i32]
>
> Explicit -fno-discard-value-names:
> define i32 @core_sys_select(i32 %n, ptr %inp, ptr %outp, ptr %exp,
> ptr %end_time) {
> %expire.i = alloca i64
> %table.i = alloca %struct.poll_wqueues
> %stack_fds = alloca [64 x i32]
>
> The rule for generating human readable LLVM IR (.ll) is only useful as a
> debugging feature:
>
> $ make LLVM=1 fs/select.ll
>
> Clang defaults to -fdiscard-value-names to save memory when generating
> LLVM IR. For debugging purposes, the improvement in readability at a
> cost of more verbose IR is a cost we're happy to pay.
>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Thanks for the patch!
Link: https://github.com/ClangBuiltLinux/linux/issues/1467
Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
> scripts/Makefile.build | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 27be77c0d6d8..d0e4f476dfee 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -140,7 +140,7 @@ $(obj)/%.symtypes : $(src)/%.c FORCE
> # LLVM assembly
> # Generate .ll files from .c
> quiet_cmd_cc_ll_c = CC $(quiet_modtag) $@
> - cmd_cc_ll_c = $(CC) $(c_flags) -emit-llvm -S -o $@ $<
> + cmd_cc_ll_c = $(CC) $(c_flags) -emit-llvm -S -fno-discard-value-names -o $@ $<
>
> $(obj)/%.ll: $(src)/%.c FORCE
> $(call if_changed_dep,cc_ll_c)
>
> base-commit: 93ed07a23fd08b8613f64cf0a15d7fbdaca010fd
> --
> 2.38.0.rc2.412.g84df46c1b4-goog
>
