Weren't all these problems solved in 1980?

1. The relative cost of operations has changed radically since the early 1980's. On a VAX 11/780, for example, floating-point multiply was expensive and memory operations had no wait states. Today, memory operations are expensive and floating-point multiplies can usually be issued every cycle. On some machines, certain categories of branches are effectively free. Different cost structures make different code sequences desirable. They also make performance sensitive to issues that were insignificant in the past.

2. Today's microprocessors achieve their high performance by relying on a number of features that were not popular on minicomputers and microcomputers in the early 1980's. Examples include non-allocating load and store instructions and the ability to issue several instructions in each cycle. (Some of these features appeared in mainframes and supercomputers in the 1960's and 1970's; those machines included hardware to manage them, like the "scoreboard" in the CDC 6600. Today's microprocessors rely on the compiler to manage these resources.) Compilers must be able to use these features.

3. Compiler-based static analysis techniques have improved steadily in the last decade. Dependence analysis, static single assignment form, and interprocedural analysis have all found their way into commercial compilers. These tools provide the optimizer and code generator with sharper information about the flow of values; this, in turn, can lead to improved run-time performance.

So, the short answer is that, in 1980, many of these problems were solved, but innovations in microprocessors and their compilers have made seeking new solutions important.