[Vm-dev] dangerous translation of MiscPrimitivePlugin code

[Nicolas Cellier]

Hi,
I don't know if it was reported yet, but we've got some nasty UB detected
by C Compiler warning in primitiveFindSubstring:

../../src/plugins/MiscPrimitivePlugin/MiscPrimitivePlugin.c:745:53:
warning: unsequenced modification and access to 'index' [-Wunsequenced]
                        while ((body[startIndex + index]) == (key[(index +=
1)])) {

Effectively, the sequence is well defined in Smalltalk, not in C.
See String>>#findSubstring:in:startingAt:matchTable:

    (body at: startIndex + index) == (key at: (index := index + 1))

Since the CCodeGenerator does not handle this,
we should better decompose the Smalltalk code into several instructions.

Hint: mind the C compiler warnings, some of them are true positive!
Half my changes/fixes are driven by them.

Nicolas
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