Following some recent discussions, this changes the representation
of callbrs in IR. The current blockaddress arguments are replaced
with `!` label constraints that refer directly to callbr indirect
destinations:
; Before:
%res = callbr i8* asm "", "=r,r,i"(i8* %x, i8* blockaddress(@test8, %foo))
to label %asm.fallthrough [label %foo]
; After:
%res = callbr i8* asm "", "=r,r,!i"(i8* %x)
to label %asm.fallthrough [label %foo]
The benefit of this is that we can easily update the successors of
a callbr, without having to worry about also updating blockaddress
references. This should allow us to remove some limitations:
* Allow unrolling/peeling/rotation of callbr, or any other
clone-based optimizations
(https://github.com/llvm/llvm-project/issues/41834)
* Allow duplicate successors
(https://github.com/llvm/llvm-project/issues/45248)
This is just the IR representation change though, I will follow up
with patches to remove limtations in various transformation passes
that are no longer needed.
Differential Revision: https://reviews.llvm.org/D129288
Fix bug exposed by https://reviews.llvm.org/D125990
rewriteLoopExitValues calls InductionDescriptor::isInductionPHI which requires
the PHI node to have an incoming edge from the loop preheader. This adds checks
before calling InductionDescriptor::isInductionPHI to see that the loop has a
preheader. Also did some refactoring.
Differential Revision: https://reviews.llvm.org/D129297
Loop Strength Reduce sometimes optimizes away all uses of an induction variable
from a loop but leaves the IV increments. When the only remaining use of the IV
is the PHI in the exit block, this patch will call rewriteLoopExitValues to
replace the exit block PHI with the final value of the IV to skip the updates
in each loop iteration.
Differential Revision: https://reviews.llvm.org/D118808
