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Simon Peyton Jones authored
Trac #13032 pointed out that we sometimes generate unused bindings for Givens, and (worse still) we can't always discard them later (we don't drop a case binding unless we can prove that the scrutinee is non-bottom. It looks as if this may be a major reason for the performace problems in #14338 (see comment:29). This patch fixes the problem at source, by pruning away all the dead Givens. See Note [Delete dead Given evidence bindings] Remarkably, compiler allocation falls by 23% in perf/compiler/T12227! I have not confirmed whether this change actualy helps with
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