Use lengthIs and friends in more places

While investigating #12545, I discovered several places in the code
that performed length-checks like so:

```
length ts == 4
```

This is not ideal, since the length of `ts` could be much longer than 4,
and we'd be doing way more work than necessary! There are already a slew
of helper functions in `Util` such as `lengthIs` that are designed to do
this efficiently, so I found every place where they ought to be used and
did just that. I also defined a couple more utility functions for list
length that were common patterns (e.g., `ltLength`).

Test Plan: ./validate

Reviewers: austin, hvr, goldfire, bgamari, simonmar

Reviewed By: bgamari, simonmar

Subscribers: goldfire, rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3622

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/nativeGen/Dwarf/Types.hs b/compiler/nativeGen/Dwarf/Types.hs
index d4d8e2429e..bc278b119e 100644
--- a/compiler/nativeGen/Dwarf/Types.hs
+++ b/compiler/nativeGen/Dwarf/Types.hs
@@ -32,6 +32,7 @@ import Platform
 import Unique
 import Reg
 import SrcLoc
+import Util
 
 import Dwarf.Constants
 
@@ -577,7 +578,7 @@ pprString' str = text "\t.asciz \"" <> str <> char '"'
 pprString :: String -> SDoc
 pprString str
   = pprString' $ hcat $ map escapeChar $
-    if utf8EncodedLength str == length str
+    if str `lengthIs` utf8EncodedLength str
     then str
     else map (chr . fromIntegral) $ bytesFS $ mkFastString str