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Update phis in AMDGPUUnifyDivergentExitNodes

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Original patch https://reviews.llvm.org/D63659 from
Steven Perron <stevenperron@google.com>

The pass AMDGPUUnifyDivergentExitNodes does not update the phi nodes in
the successors of blocks that is splits. This is fixed by calling
BasicBlock::splitBasicBlock to split the block instead of doing it
manually. This does extra work because a new conditional branch is
created in BB which is immediately replaced, but I think the simplicity
is worth it. It also helps make the code more future proof in case other
things need to be updated.

llvm-svn: 364342
This commit is contained in:
Diego Novillo 2019-06-25 18:55:16 +00:00
parent d6967bf53e
commit f6dfb7cc75
2 changed files with 43 additions and 7 deletions
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11
lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
View File

@ -198,14 +198,11 @@ bool AMDGPUUnifyDivergentExitNodes::runOnFunction(Function &F) {
BranchInst::Create(LoopHeaderBB, DummyReturnBB, BoolTrue, BB);
} else { // Conditional branch.
// Create a new transition block to hold the conditional branch.
BasicBlock *TransitionBB = BasicBlock::Create(F.getContext(),
"TransitionBlock", &F);
BasicBlock *TransitionBB = BB->splitBasicBlock(BI, "TransitionBlock");
// Move BI from BB to the new transition block.
BI->removeFromParent();
TransitionBB->getInstList().push_back(BI);
// Create a branch that will always branch to the transition block.
// Create a branch that will always branch to the transition block and
// references DummyReturnBB.
BB->getTerminator()->eraseFromParent();
BranchInst::Create(TransitionBB, DummyReturnBB, BoolTrue, BB);
}
}

39
test/CodeGen/AMDGPU/update-phi.ll Normal file
View File

@ -0,0 +1,39 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -mtriple=amdgcn-- -S -amdgpu-unify-divergent-exit-nodes -verify %s | FileCheck -check-prefix=IR %s
; Make sure that the phi in n28 is updated when the block is split by unify
; divergent exit nodes.
define amdgpu_ps void @_amdgpu_ps_main() local_unnamed_addr #3 {
; IR-LABEL: @_amdgpu_ps_main(
; IR-NEXT: .entry:
; IR-NEXT: br label [[DOTLOOPEXIT:%.*]]
; IR: .loopexit:
; IR-NEXT: br label [[N28:%.*]]
; IR: n28:
; IR-NEXT: [[DOT01:%.*]] = phi float [ 0.000000e+00, [[DOTLOOPEXIT]] ], [ [[N29:%.*]], [[TRANSITIONBLOCK:%.*]] ]
; IR-NEXT: [[N29]] = fadd float [[DOT01]], 1.000000e+00
; IR-NEXT: [[N30:%.*]] = fcmp ogt float [[N29]], 4.000000e+00
; IR-NEXT: br i1 true, label [[TRANSITIONBLOCK]], label [[DUMMYRETURNBLOCK:%.*]]
; IR: TransitionBlock:
; IR-NEXT: br i1 [[N30]], label [[DOTLOOPEXIT]], label [[N28]]
; IR: n31:
; IR-NEXT: ret void
; IR: DummyReturnBlock:
; IR-NEXT: ret void
;
.entry:
br label %.loopexit
.loopexit: ; preds = %n28, %.entry
br label %n28
n28: ; preds = %.loopexit, %n28
%.01 = phi float [ 0.000000e+00, %.loopexit ], [ %n29, %n28 ]
%n29 = fadd float %.01, 1.0
%n30 = fcmp ogt float %n29, 4.000000e+00
br i1 %n30, label %.loopexit, label %n28
n31: ; preds =
ret void
}