Commits on Oct 21, 2020

1. wasm->CLIF translation: consistently bitcast V128 values that are blo… …

   …ck formal parameters.
   
   In the current translation of wasm (128-bit) SIMD into CLIF, we work around differences in the
   type system models of wasm vs CLIF by inserting `bitcast` (a no-op cast) CLIF instructions before
   more or less every use of a SIMD value.  Unfortunately this was not being done consistently and
   even small examples with a single if-then-else diamond that produces a SIMD value, could cause a
   verification failure downstream.  In this case, the jump out of the "else" block needed a
   bitcast, but didn't have one.
   
   This patch wraps creation of CLIF jumps and conditional branches up into three functions,
   `canonicalise_then_jump` and `canonicalise_then_br{z,nz}`, and uses them consistently.  They
   first cast the relevant block formal parameters, then generate the relevant kind of branch/jump.
   Hence, provided they are also used consistently in future to generate branches/jumps in this
   file, we are protected against such failures.
   
   The patch also adds a large(ish) comment at the top explaining this in more detail.

   

   julian-seward1 committed Oct 21, 2020
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