<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Mar 5, 2015, at 1:01 PM, Duncan P. N. Exon Smith <<a href="mailto:dexonsmith@apple.com" class="">dexonsmith@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class="Apple-interchange-newline">On 2015 Feb 26, at 11:34, Eric Christopher <<a href="mailto:echristo@gmail.com" class="">echristo@gmail.com</a>> wrote:<br class=""><br class=""><br class=""><br class="">On Tue, Feb 24, 2015 at 3:18 PM Sean Silva <<a href="mailto:chisophugis@gmail.com" class="">chisophugis@gmail.com</a>> wrote:<br class="">On Tue, Feb 24, 2015 at 2:53 PM, Duncan P. N. Exon Smith <<a href="mailto:dexonsmith@apple.com" class="">dexonsmith@apple.com</a>> wrote:<br class=""><br class=""><blockquote type="cite" class="">On 2015-Feb-24, at 13:25, Eric Christopher <<a href="mailto:echristo@gmail.com" class="">echristo@gmail.com</a>> wrote:<br class=""><br class="">Hi Duncan,<br class=""><br class="">Been thinking about this a bit and a few comments/questions. I may have misunderstood some things in your mail though so please feel free to explain at me :)<br class=""><br class=""><br class="">Changing `clang` to store target defaults on the module will allow us to<br class="">continue to override them when running `llc`. The right precedence<br class="">would be:<br class=""><br class=""> 1. Explicit attributes set on the function.<br class=""> 2. `llc` command-line options.<br class=""> 3. Default function attributes stored on the module.<br class=""><br class="">(Outside of `llc`, skip step 2.)<br class=""><br class="">In `lib/Linker` (i.e., `llvm-lto`, `llvm-link`, `libLTO.dylib`),<br class="">defaults should be pushed down as explicit function attributes.<br class=""><br class="">I think there are a few options/backend communications that aren't/haven't gone this way yet that are probably worth considering:<br class=""><br class="">MCTargetOptions/TargetOptions: Basically a grab bag of functionality, some of which is duplicated via attributes and some that's not. I think at least some of these should be replaced by module flags, e.g. ABI.<br class=""><br class="">Random backend flags: Anything for debugging.<br class=""><br class="">I'm thinking things that are either set as Init(true/false) and affect things at a global level and not just the function level.<br class=""></blockquote><br class="">(I think my lib/Linker comment was unclear. See below.)<br class=""><br class="">Not at all trying to say that *everything* should be a function<br class="">attribute; global-level stuff should absolutely be module flags.<br class=""><br class="">I'm just talking about infrastructure for the things that *are*<br class="">function-level.<br class=""><br class=""><blockquote type="cite" class=""><br class="">They look like this in assembly:<br class=""><br class=""> attributes default = { "no-frame-pointer-elim"="false" }<br class=""><br class=""><br class="">So, how do you see module merging and defaults working? (Yes, there were testcases, but let's go with prose here. I found the testcases a bit hard to reason.)<br class=""></blockquote><br class="">This is where my lib/Linker comment applies:<br class=""><br class=""><blockquote type="cite" class=""><blockquote type="cite" class="">In `lib/Linker` (i.e., `llvm-lto`, `llvm-link`, `libLTO.dylib`),<br class="">defaults should be pushed down as explicit function attributes.<br class=""></blockquote></blockquote><br class="">^ This is how I see module merging and defaults working: push the<br class="">defaults down to explicit function attributes. So there wouldn't<br class="">be any default function attributes in the output of `llvm-link`.<br class="">This means that `llc` will still have trouble overriding attributes<br class="">in the output of merged modules -- but at least it can handle the<br class="">output of `clang` without trouble. In the future we could try to<br class="">be more intelligent about merged modules, and keep common options<br class="">in the default set.<br class=""><br class=""><blockquote type="cite" class=""><br class="">Limitations<br class="">===========<br class=""><br class="">There are a few limitations with this approach (at least, with my<br class="">reference implementation).<br class=""><br class=""> - `Function::getAttributes()` only reflects the explicitly specified<br class=""> attributes, skipping those set as module defaults.<br class=""><br class="">Ick. Pretty severe limitation? I.e. how would it work to test general attributes on a function during code gen?<br class=""></blockquote><br class="">As long as everyone calls `Function::hasFnAttribute()`, there's no<br class="">problem. This proposal basically turns it into a bug to access<br class="">them directly; you need to go through `Function::hasFnAttribute()`<br class="">to get the right answer. (Not sure if there's a better way?)<br class=""><br class=""><blockquote type="cite" class=""><br class=""> - If an enum attribute is set as a default, there's no way for a<br class=""> function-attribute to override it. In practice, we could avoid the<br class=""> feature for enum attributes.<br class=""><br class="">Hrm. This seems like a pretty severe limitation? Anything come to mind in practice.<br class=""></blockquote><br class="">In the `Attribute` format, mutually exclusive attributes aren't<br class="">related at all (they're not inherently mutually exclusive). To<br class="">make them overridable, we'd need a completely new design for<br class="">enum attributes.<br class=""><br class="">As a result, this proposal only improves `llc` for string-based<br class="">attributes. I don't see that as a problem... the string-based<br class="">attributes are more flexible anyway. Maybe `Module` should only<br class="">allow `setDefaultFnAttribute()` for string attributes though?<br class=""><br class="">(Some more context on why enum attributes can't really be<br class="">overridden. This isn't just a problem for enum attributes that<br class="">are mutually exclusive. Consider:<br class=""><br class=""> attributes defaults = { noreturn }<br class=""><br class="">Besides being somewhat insane, there's no `return` attribute,<br class="">so you can't really override it. I suppose one idea would be to<br class="">explicitly mark a function `~noreturn` or something:<br class=""><br class=""> define void @foo() ~noreturn { ; Ignore module default noreturn.<br class=""><br class="">Not sure if this direction is a good one though.)<br class=""><br class=""><blockquote type="cite" class=""><br class=""> - `CallSite` instructions store function-level attributes, but don't<br class=""> forward to the module-level defaults. There are places (like the<br class=""> calls to `EmitUnaryFloatFnCall()` in `-simplify-libcalls`) where we<br class=""> use the callee function attributes to set the call site attributes.<br class=""> In practice, we could avoid the feature for attributes that are<br class=""> meaningful for call sites.<br class=""><br class="">Sure.<br class=""><br class=""> - Intrinsics' attributes are independent of `CodeGenOptions`, and set<br class=""> via `Instrinsic::getAttributes()`. With this change they'd inherit<br class=""> the default attributes like other functions. Is this a problem?<br class=""> If so, we can add a flag on `Function` that inhibits forwarding to<br class=""> the defaults.<br class=""><br class=""><br class="">Seems reasonable.<br class=""><br class="">Thoughts? Other ideas for solving the `llc` problem?<br class=""><br class=""><br class="">I think this is a good start, I think I'd like to worry about some of the other issues in advance before we start incrementally changing things though. (Also, I really have no other ideas :)<br class=""><br class=""></blockquote><br class=""><br class="">So Akira had an idea at the end of last week that I don't<br class="">think made it onto the list, and it's worth considering as an<br class="">alternative:<br class=""><br class="">Add a bit to attributes indicating whether or not they're<br class="">overridable (i.e., they're overridable if they're target<br class="">defaults; they're not overridable if they've been explicitly<br class="">specified somehow).<br class=""><br class="">Here's some straw-man syntax:<br class=""><br class=""> attributes #0 = { noreturn ssp? "att1"="1" "att2"="2"? }<br class=""><br class="">Where:<br class=""><br class=""> - `noreturn` and `"att1"="1"` are required.<br class=""> - `ssp` and `"att2"="2"` can be overridden (e.g., by `llc`).<br class=""><br class="">(Alternately, but equivalently:<br class=""><br class=""> attributes #0 = { noreturn! ssp "att1"="1"! "att2"="2" }<br class=""><br class="">I like this syntax better, but it would cause more churn, and<br class="">`!` is so far reserved for metadata.)<br class=""><br class="">Whatever the syntax, the idea is: `llc` resets/deletes<br class="">attributes on every function to match what's specified on the<br class="">command-line. In the above example, functions with attribute<br class="">set #0 could have `ssp` and `"att2"` overridden via the `llc`<br class="">command-line, but not `noreturn` and `"att1"`.<br class=""><br class="">To compare it to my proposal:<br class=""><br class=""> - Storing a default attribute set (my proposal) makes it<br class=""> easier to look at and set the defaults. Applying `llc`<br class=""> command-line options is easy, too -- just override the<br class=""> default attribute set on the module -- although it doesn't<br class=""> really work on the output of `lib/Linker`.<br class=""> - Storing a bit on each attribute (Akira's proposal) handles<br class=""> more cases. Nothing needs to be done in `lib/Linker`<br class=""> (`llc` is able to override the output of `llvm-link`),<br class=""> and it doesn't have a disconnect between `hasFnAttribute()`<br class=""> and `getAttributes().hasAttribute(FunctionIndex)`.<br class=""><br class="">Awkwardly, having written that out, I'm kind of leaning toward<br class="">it myself right now (maybe I'm fickle?) -- it seems to have<br class="">fewer limitations. The main thing I prefer about my proposal<br class="">is that it's easier to change the default attributes when<br class="">modifying an assembly file by hand, but I suppose we could<br class="">write a tool for that?<br class=""><br class="">I think the tool approach deserves a bit of attention for the original usecase of trying different target attributes to see if they tickle a bug. Would it be feasible to have a purpose-built tool `llvm-attr-mutate` (bikeshed) so you can do `cat foo.bc | llvm-attr-mutate .... | llc`. The arguments to llvm-attr-mutate could then be made as convenient/powerful as needed for this debugging task.<br class=""><br class=""><br class="">FWIW the tool approach is what we were coming up with in the first place :)<br class=""><br class="">Which would obviate the need for handling the command line options at all of course.<br class=""><br class=""></blockquote><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">I've done some more thinking about this.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">1. The module-level default attribute approach (what I started this</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> thread with) cleans up assembly files and provides a clean hook for</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> mutating the "defaults" from `llc`. However, it doesn't cleanly fit</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> into the current semantic model for attributes, so you get weird</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> inconsistencies depending on how you query them.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">2. Flipping a bit to indicate whether something was the "default"</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> solves the various technical problems. However, overriding the</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> attributes requires walking all of the IR to rewrite them, and the</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> assembly syntax readability will get worse, not better.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">3. Using a separate tool allows you to override the attributes</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> arbitrarily, but doesn't distinguish between "default" and explicit</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> attributes. Furthermore, if the primary use for the tool is:</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> llvm-attr-mutate -o - t.bc -attr target-cpu=proc123 | llc</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> then I'm not sure we're gaining anything. In particular, having</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> `llc` mutate the IR when you say:</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> llc <t.bc -target-cpu=proc123</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> is a far cleaner interface. Not to say that a tool to mutate</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> attributes isn't a great idea -- I think it might be -- just that</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> it's not a great solution for *this* problem.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">4. Having `llc` mutate the IR itself -- the obvious solution, which</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> Akira posted a patch for a few months ago -- does the job just as</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> well as `llvm-attr-mutate` but with a much cleaner interface. It</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> fails to distinguish between target defaults and explicit</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> attributes, but when combined with `llvm-extract`, it gives you full</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class=""> control over the codegen options for each function.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Remind me again why we don't just do #4? It seems like the simplest way</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">to keep `llc` viable in the short term.</span></div></blockquote><br class=""></div><div><br class=""></div><div>llc should be able to override the default values for options without mutating anything that’s explicitly specified at a function (or module) level.</div><div><br class=""></div><div>For example, if I have a .ll file with specialized functions with different CPUs specified, I want to be able to recompile that file with -mcpu= on the llc command line in such a way that those functions don’t get changed, but any functions that don’t have an explicit CPU on them do. Consider trying to test something like function multi versioning.</div><div><br class=""></div><div>-Jim</div><br class=""></body></html>