Merge 6b2fd7aed66d592738f26c76caa8fff95e168598 into 18.x

[brad0]

[MIPS] Use generic isBlockOnlyReachableByFallthrough (#80799)

FastISel may create a redundant BGTZ terminal which fallthroughes.

  BGTZ %2:gpr32, %bb.1, implicit-def $at

bb.1.bb1:
; predecessors: %bb.0

The !I->isBarrier() check in
MipsAsmPrinter::isBlockOnlyReachableByFallthrough
will incorrectly not print a label, leading to a Undefined temporary symbol
error when we try assembling the output assembly file. See the updated
Fast-ISel/pr40325.ll and
rust-lang/rust#108835

In addition, the SwitchInst condition is too conservative and prints
many unneeded labels (see the updated tests).

Just use the generic isBlockOnlyReachableByFallthrough, updated by
commit 1995b9f for SPARC, which also
handles MIPS.

[brad0]

/cherry-pick 6b2fd7a

[llvmbot]

/pull-request #80878

[llvmbot]

@llvm/issue-subscribers-backend-mips

Author: Brad Smith (brad0)

[MIPS] Use generic isBlockOnlyReachableByFallthrough (#80799)

FastISel may create a redundant BGTZ terminal which fallthroughes.

  BGTZ %2:gpr32, %bb.1, implicit-def $at

bb.1.bb1:
; predecessors: %bb.0

The !I->isBarrier() check in
MipsAsmPrinter::isBlockOnlyReachableByFallthrough
will incorrectly not print a label, leading to a Undefined temporary symbol
error when we try assembling the output assembly file. See the updated
Fast-ISel/pr40325.ll and
rust-lang/rust#108835

In addition, the SwitchInst condition is too conservative and prints
many unneeded labels (see the updated tests).

Just use the generic isBlockOnlyReachableByFallthrough, updated by
commit 1995b9f for SPARC, which also
handles MIPS.