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* cmd/gc: correct liveness for fat variablesRuss Cox2014-02-151-6/+22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The VARDEF placement must be before the initialization but after any final use. If you have something like s = ... using s ... the rhs must be evaluated, then the VARDEF, then the lhs assigned. There is a large comment in pgen.c on gvardef explaining this in more detail. This CL also includes Ian's suggestions from earlier CLs, namely commenting the use of mode in link.h and fixing the precedence of the ~r check in dcl.c. This CL enables the check that if liveness analysis decides a variable is live on entry to the function, that variable must be a function parameter (not a result, and not a local variable). If this check fails, it indicates a bug in the liveness analysis or in the generated code being analyzed. The race detector generates invalid code for append(x, y...). The code declares a temporary t and then uses cap(t) before initializing t. The new liveness check catches this bug and stops the compiler from writing out the buggy code. Consequently, this CL disables the race detector tests in run.bash until the race detector bug can be fixed (golang.org/issue/7334). Except for the race detector bug, the liveness analysis check does not detect any problems (this CL and the previous CLs fixed all the detected problems). The net test still fails with GOGC=0 but the rest of the tests now pass or time out (because GOGC=0 is so slow). TBR=iant CC=golang-codereviews https://codereview.appspot.com/64170043
* cmd/gc: correct liveness for wrappers containing tail jumpsRuss Cox2014-02-131-0/+30
A normal RET is treated as using the return values, but a tail jump RET does not - it is jumping to the function that is going to fill in the return values. If a tail jump RET is recorded as using the return values, since nothing initializes them they will be marked as live on entry to the function, which is clearly wrong. Found and tested by the new code in plive.c that looks for variables that are incorrectly live on entry. That code is disabled for now because there are other cases remaining to be fixed. But once it is enabled, test/live1.go becomes a real test of this CL. TBR=iant CC=golang-codereviews https://codereview.appspot.com/63570045