5f6172f068
CreateControlFlowHub is a method that redirects control flow edges from a set of incoming blocks to a set of outgoing blocks through a new set of "guard" blocks. This is now refactored into a separate file with one enhancement: The input to the method is now a set of branches rather than two sets of blocks. The original implementation reroutes every edge from incoming blocks to outgoing blocks. But it is possible that for some incoming block InBB, some successor S might be in the set of outgoing blocks, but that particular edge should not be rerouted. The new implementation makes this possible by allowing the user to specify the targets of each branch that need to be rerouted. This is needed when improving the implementation of FixIrreducible #101386. Current use in FixIrreducible does not demonstrate this finer control over the edges being rerouted. But in UnifyLoopExits, when only one successor of an exiting block is an exit block, this refinement now reroutes only the relevant control-flow through the edge; the non-exit successor is not rerouted. This results in fewer branches and PHI nodes in the hub.
175 lines
7.0 KiB
LLVM
175 lines
7.0 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -unify-loop-exits -structurizecfg -S | FileCheck %s
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; The structurizer uses an RPO traversal over a region, along with a
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; manual hack that is meant to sort ensure that blocks within a loop
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; are all visited before visiting blocks outside the loop. But this
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; does not always work as expected. For example the results are
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; incorrect when multiple nested loops are involved.
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; The workaround for this is to unify loop exits. Each loop now
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; becomes an SESE region with a single header and a single exit. The
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; structurizer is a region pass, and it no longer sees the entire loop
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; nest in a single region. More importantly, for each loop, the only
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; block reachable outside the loop is the region exit, which avoids
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; any confusion in the hacked RPO traversal.
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; In the function below, B1 is an exiting block in outer loop H1. It's
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; successor inside the loop is the header of another loop H2. Due to
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; the incorrect traversal, B1 dominates all the blocks in the
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; structurized program, except the header H1.
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define void @exiting-block(i1 %PredH1, i1 %PredB2, i1 %PredB1, i1 %PredH2) {
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; CHECK-LABEL: @exiting-block(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[PREDH1_INV:%.*]] = xor i1 [[PREDH1:%.*]], true
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; CHECK-NEXT: [[PREDB2_INV:%.*]] = xor i1 [[PREDB2:%.*]], true
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; CHECK-NEXT: br label [[H1:%.*]]
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; CHECK: H1:
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; CHECK-NEXT: br i1 [[PREDH1_INV]], label [[B1:%.*]], label [[FLOW3:%.*]]
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; CHECK: Flow3:
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; CHECK-NEXT: [[TMP0:%.*]] = phi i1 [ true, [[B1]] ], [ undef, [[H1]] ]
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; CHECK-NEXT: [[TMP1:%.*]] = phi i1 [ [[PREDB1:%.*]], [[B1]] ], [ [[PREDH1]], [[H1]] ]
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; CHECK-NEXT: br i1 [[TMP1]], label [[H2:%.*]], label [[FLOW4:%.*]]
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; CHECK: H2:
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; CHECK-NEXT: br i1 [[PREDH2:%.*]], label [[B2:%.*]], label [[FLOW:%.*]]
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; CHECK: B2:
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; CHECK-NEXT: br i1 [[PREDB2_INV]], label [[L2:%.*]], label [[FLOW2:%.*]]
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; CHECK: Flow:
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; CHECK-NEXT: [[TMP2:%.*]] = phi i1 [ false, [[FLOW2]] ], [ true, [[H2]] ]
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; CHECK-NEXT: [[TMP3:%.*]] = phi i1 [ [[TMP5:%.*]], [[FLOW2]] ], [ true, [[H2]] ]
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; CHECK-NEXT: br i1 [[TMP3]], label [[LOOP_EXIT_GUARD1:%.*]], label [[H2]]
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; CHECK: L2:
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; CHECK-NEXT: br label [[FLOW2]]
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; CHECK: L1:
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; CHECK-NEXT: br label [[FLOW5:%.*]]
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; CHECK: B1:
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; CHECK-NEXT: br label [[FLOW3]]
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; CHECK: C:
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; CHECK-NEXT: br label [[EXIT:%.*]]
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; CHECK: exit:
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; CHECK-NEXT: ret void
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; CHECK: Flow5:
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; CHECK-NEXT: [[TMP4:%.*]] = phi i1 [ false, [[L1:%.*]] ], [ true, [[LOOP_EXIT_GUARD1]] ]
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; CHECK-NEXT: br label [[FLOW4]]
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; CHECK: loop.exit.guard:
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; CHECK-NEXT: br i1 [[TMP6:%.*]], label [[C:%.*]], label [[EXIT]]
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; CHECK: Flow2:
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; CHECK-NEXT: [[TMP5]] = phi i1 [ false, [[L2]] ], [ true, [[B2]] ]
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; CHECK-NEXT: br label [[FLOW]]
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; CHECK: Flow4:
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; CHECK-NEXT: [[TMP6]] = phi i1 [ false, [[FLOW5]] ], [ [[TMP0]], [[FLOW3]] ]
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; CHECK-NEXT: [[TMP7:%.*]] = phi i1 [ [[TMP4]], [[FLOW5]] ], [ true, [[FLOW3]] ]
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; CHECK-NEXT: br i1 [[TMP7]], label [[LOOP_EXIT_GUARD:%.*]], label [[H1]]
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; CHECK: loop.exit.guard1:
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; CHECK-NEXT: br i1 [[TMP2]], label [[L1]], label [[FLOW5]]
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;
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entry:
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br label %H1
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H1: ; preds = %L1, %entry
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br i1 %PredH1, label %H2, label %B1
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H2: ; preds = %B1, %L2, %H1
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br i1 %PredH2, label %B2, label %L1
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B2: ; preds = %H2
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br i1 %PredB2, label %exit, label %L2
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L2: ; preds = %B2
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br label %H2
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L1: ; preds = %H2
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br label %H1
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B1: ; preds = %H1
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br i1 %PredB1, label %H2, label %C
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C: ; preds = %B1
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br label %exit
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exit: ; preds = %C, %B2
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ret void
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}
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; The function below has three nested loops. Due to the incorrect
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; traversal, H2 dominates H3 in the structurized program, and the
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; backedge from L13 to H3 has no equivalent path.
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define void @incorrect-backedge(i1 %PredH2, i1 %PredH3, i1 %PredL2, i1 %PredL13, i1 %PredL1)
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; CHECK-LABEL: @incorrect-backedge(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[PREDH2_INV:%.*]] = xor i1 [[PREDH2:%.*]], true
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; CHECK-NEXT: [[PREDL2_INV:%.*]] = xor i1 [[PREDL2:%.*]], true
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; CHECK-NEXT: [[PREDH3_INV:%.*]] = xor i1 [[PREDH3:%.*]], true
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; CHECK-NEXT: [[PREDL13_INV:%.*]] = xor i1 [[PREDL13:%.*]], true
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; CHECK-NEXT: br label [[H1:%.*]]
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; CHECK: H1:
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; CHECK-NEXT: br label [[H2:%.*]]
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; CHECK: H2:
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; CHECK-NEXT: br i1 [[PREDH2_INV]], label [[H3:%.*]], label [[FLOW4:%.*]]
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; CHECK: H3:
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; CHECK-NEXT: br i1 [[PREDH3_INV]], label [[L2:%.*]], label [[FLOW:%.*]]
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; CHECK: L2:
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; CHECK-NEXT: br i1 [[PREDL2_INV]], label [[L13:%.*]], label [[FLOW3:%.*]]
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; CHECK: Flow:
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; CHECK-NEXT: [[TMP0:%.*]] = phi i1 [ [[TMP6:%.*]], [[FLOW3]] ], [ true, [[H3]] ]
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; CHECK-NEXT: [[TMP1:%.*]] = phi i1 [ false, [[FLOW3]] ], [ true, [[H3]] ]
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; CHECK-NEXT: [[TMP2:%.*]] = phi i1 [ [[TMP7:%.*]], [[FLOW3]] ], [ true, [[H3]] ]
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; CHECK-NEXT: br i1 [[TMP2]], label [[LOOP_EXIT_GUARD2:%.*]], label [[H3]]
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; CHECK: L13:
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; CHECK-NEXT: br label [[FLOW3]]
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; CHECK: Flow5:
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; CHECK-NEXT: [[TMP3:%.*]] = phi i1 [ [[TMP8:%.*]], [[LOOP_EXIT_GUARD1:%.*]] ], [ true, [[LOOP_EXIT_GUARD:%.*]] ]
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; CHECK-NEXT: [[TMP4:%.*]] = phi i1 [ false, [[LOOP_EXIT_GUARD1]] ], [ true, [[LOOP_EXIT_GUARD]] ]
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; CHECK-NEXT: br i1 [[TMP4]], label [[L1:%.*]], label [[FLOW6:%.*]]
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; CHECK: L1:
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; CHECK-NEXT: br label [[FLOW6]]
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; CHECK: Flow6:
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; CHECK-NEXT: [[TMP5:%.*]] = phi i1 [ [[PREDL1:%.*]], [[L1]] ], [ [[TMP3]], [[FLOW5:%.*]] ]
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; CHECK-NEXT: br i1 [[TMP5]], label [[EXIT:%.*]], label [[H1]]
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; CHECK: exit:
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; CHECK-NEXT: ret void
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; CHECK: loop.exit.guard:
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; CHECK-NEXT: br i1 [[DOTINV:%.*]], label [[LOOP_EXIT_GUARD1]], label [[FLOW5]]
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; CHECK: loop.exit.guard1:
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; CHECK-NEXT: br label [[FLOW5]]
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; CHECK: Flow3:
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; CHECK-NEXT: [[TMP6]] = phi i1 [ true, [[L13]] ], [ false, [[L2]] ]
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; CHECK-NEXT: [[TMP7]] = phi i1 [ [[PREDL13_INV]], [[L13]] ], [ true, [[L2]] ]
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; CHECK-NEXT: br label [[FLOW]]
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; CHECK: Flow4:
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; CHECK-NEXT: [[TMP8]] = phi i1 [ [[TMP1]], [[LOOP_EXIT_GUARD2]] ], [ false, [[H2]] ]
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; CHECK-NEXT: [[TMP9:%.*]] = phi i1 [ false, [[LOOP_EXIT_GUARD2]] ], [ true, [[H2]] ]
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; CHECK-NEXT: [[TMP10:%.*]] = phi i1 [ [[TMP0]], [[LOOP_EXIT_GUARD2]] ], [ true, [[H2]] ]
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; CHECK-NEXT: [[DOTINV]] = xor i1 [[TMP9]], true
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; CHECK-NEXT: br i1 [[TMP10]], label [[LOOP_EXIT_GUARD]], label [[H2]]
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; CHECK: loop.exit.guard2:
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; CHECK-NEXT: br label [[FLOW4]]
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;
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{
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entry:
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br label %H1
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H1:
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br label %H2
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H2:
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br i1 %PredH2, label %L1, label %H3
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H3:
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br i1 %PredH3, label %exit, label %L2
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L2:
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br i1 %PredL2, label %H2, label %L13
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L13:
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br i1 %PredL13, label %H3, label %H1
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L1:
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br i1 %PredL1, label %exit, label %H1
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exit:
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ret void
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}
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