Compile time was measured. My favorite "bug" was the
many minutes it took to compile a constant expression
that involved shifting a constant INT_MAX bits by
performing that many 1-bit shifts.

I don't know if this anecdote is an urban legend or if it really
happened. I was told [a similar] story when I was interning as an operator
at my alma mater, which was an IBM System/360 shop.

I heard it not from the grapevine, but from McKeeman himself.

It’s mentioned in the paper (https://www.hpl.hp.com/hpjournal/dtj/vol10num1/vol10num1art9.pdf) on page 105, table 1

Results of Testing C Compilers

Source Code Resulting Problem

1>>INT_MAX Twenty-minute compile time

int(…(x)…) enough nested parentheses to kill the compiler

Spurious diagnostic (10 parentheses)

Compiler crash (100 parentheses)

Server crash (10,000 parentheses)

explained on page 104:

… the server crash occurred when the tested compiler got a stack overflow on a heavily loaded machine with a very large memory. The operating system attempted to dump a gigabyte of compiler stack, which caused all the other active users to thrash, and many of them also dumped for lack of memory. The many disk drives on the server began a dance of the lights that sopped up the remaining free resources, causing the operators to boot the server to recover. Excellent testing can make you unpopular with almost everyone.