Provide reason messages for unviable inlining

[yrouban]

Summary

InlineCost's isInlineViable() is changed to return InlineResult instead of bool. This provides messages for failure reasons.
This allows to get more specific messages for cases where callsites are not viable for inlining.

[xbolva00]

lib/Analysis/InlineCost.cpp

2028 ↗

(On Diff #183045)

getNever should take a string

[yrouban]

lib/Analysis/InlineCost.cpp

2028 ↗

(On Diff #183045)

InlineResult is implicitly converted to char* Reason.
Do you propose explicit IsViable.message?

[xbolva00]

lib/Analysis/InlineCost.cpp

2028 ↗

(On Diff #183045)

Yes, readability would be better

[anemet]

This is great, please add some tests or check for remarks in existing tests (e.g. for the recursive case).

[yrouban]

Addressed comments:

• added a simple test
• changed implicit conversion to char* to explicit field access IsViable.message

[yrouban]

@anemet, @xbolva00, please take a look once again.

[xbolva00]

Looks fine for me

test/Frontend/optimization-remark-with-hotness.c

void bar(int x) {
   // NO_PGO: '-fdiagnostics-show-hotness' requires profile-guided optimization information
   // NO_PGO: '-fdiagnostics-hotness-threshold=' requires profile-guided optimization information
   // expected-remark@+1 {{foo inlined into bar with (cost=always): always inliner (hotness:}}
   sum += foo(x, x - 2);
 }
 
 int main(int argc, const char *argv[]) {
   for (int i = 0; i < 30; i++)
-    // expected-remark@+1 {{bar not inlined into main because it should never be inlined (cost=never): always inliner (hotness:}}
+    // expected-remark@+1 {{bar not inlined into main because it should never be inlined (cost=never): no alwaysinline attribute (hotness:}}
     bar(argc);
   return sum;
 }