Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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diff --git a/js/src/jit-test/tests/wasm/simd/README-codegen.md b/js/src/jit-test/tests/wasm/simd/README-codegen.md
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+About whitebox code generation tests (*-codegen.js):
+
+These test that extraneous moves are not inserted by the register
+allocator or code generator under ideal conditions: when it is in
+principle possible for the code generator and register allocator to
+use inputs where they are and generate outputs directly in the target
+registers.
+
+These tests are both limited in scope and brittle in the face of
+changes to the register allocator, but how else would we test that
+code generation and register allocation work when presented with the
+easiest case?  And if they don't work then, when will they work?
+
+For a reliable test, the inputs must be known to be in the fixed
+parameter registers and the result must be known to be desired in the
+fixed function result register.
+
+Sometimes, to test optimal codegen, we need the inputs to be in
+reversed or permuted locations so as to avoid generating moves that
+are inserted by the regalloc to adapt to the function signature.
+
+In the test cases, the expected output is expressed as a multi-line
+regular expression.  The first line of each expected output is the
+tail end of the prologue; subsequent lines comprise the operation;
+finally there is the beginning of the epilogue.  Sometimes there is
+only the end of the prologue and the beginning of the operation, as
+the operation is long and we don't care about its tail.
+