2a721374ae
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
27 lines
714 B
LLVM
27 lines
714 B
LLVM
;; RUN: opt -S -codegenprepare < %s | FileCheck %s
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;; Ensure that codegenprepare (via InstSimplify) doesn't eliminate the
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;; phi here (which would cause a module verification error).
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;; CHECK: phi
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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declare void @foo(i32)
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define dso_local i32 @futex_lock_pi_atomic() local_unnamed_addr {
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entry:
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%0 = callbr i32 asm "", "=r,!i,~{dirflag},~{fpsr},~{flags}"()
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to label %asm.fallthrough.i [label %b.exit]
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asm.fallthrough.i:
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br label %b.exit
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b.exit:
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%g.0 = phi i32 [ %0, %asm.fallthrough.i ], [ undef, %entry ]
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tail call void @foo(i32 %g.0)
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ret i32 undef
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}
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