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, 2 deletions

diff --git a/compiler/codeGen/StgCmmPrim.hs b/compiler/codeGen/StgCmmPrim.hs
index e0a68f68d8..1ecd72f9db 100644
--- a/compiler/codeGen/StgCmmPrim.hs
+++ b/compiler/codeGen/StgCmmPrim.hs
@@ -619,7 +619,7 @@ emitPrimOp dflags [res] (VecBroadcastOp vcat n w) [e] = do
 
 emitPrimOp dflags [res] (VecPackOp vcat n w) es = do
     checkVecCompatibility dflags vcat n w
-    when (length es /= n) $
+    when (es `lengthIsNot` n) $
         panic "emitPrimOp: VecPackOp has wrong number of arguments"
     doVecPackOp (vecElemInjectCast dflags vcat w) ty zeros es res
   where
@@ -637,7 +637,7 @@ emitPrimOp dflags [res] (VecPackOp vcat n w) es = do
 
 emitPrimOp dflags res (VecUnpackOp vcat n w) [arg] = do
     checkVecCompatibility dflags vcat n w
-    when (length res /= n) $
+    when (res `lengthIsNot` n) $
         panic "emitPrimOp: VecUnpackOp has wrong number of results"
     doVecUnpackOp (vecElemProjectCast dflags vcat w) ty arg res
   where