tree 49ddf31949a4a5e57f0df644066357f57dce9ea3
parent dda0a1867cc0c4ace4535f179aec85c3ff8cfa96
author Amara Emerson <amara@apple.com> 1601415594 -0700
committer Hans Wennborg <hans@chromium.org> 1601463948 +0200

[GlobalISel] Fix multiply with overflow intrinsics legalization generating invalid MIR.

During lowering of G_UMULO and friends, the previous code moved the builder's
insertion point to be after the legalizing instruction. When that happened, if
there happened to be a "G_CONSTANT i32 0" immediately after, the CSEMIRBuilder
would try to find that constant during the buildConstant(zero) call, and since
it dominates itself would return the iterator unchanged, even though the def
of the constant was *after* the current insertion point. This resulted in the
compare being generated *before* the constant which it was using.

There's no need to modify the insertion point before building the mul-hi or
constant. Delaying moving the insert point ensures those are built/CSEd before
the G_ICMP is built.

Fixes PR47679

Differential Revision: https://reviews.llvm.org/D88514

(cherry picked from commit 1d54e75cf26a4c60b66659d5d9c62f4bb9452b03)