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clang-p2996/llvm/test/Transforms/StructurizeCFG/workarounds/needs-unified-loop-exits.ll
Brendon Cahoon f59205aef9 [BasicBlockUtils] Add a new way for CreateControlFlowHub() 
The existing way of creating the predicate in the guard blocks uses
a boolean value per outgoing block. This increases the number of live
booleans as the number of outgoing blocks increases. The new way added
in this change is to store one integer to represent the outgoing block
we want to branch to, then at each guard block, an integer equality
check is performed to decide which a specific outgoing block is taken.

Using an integer reduces the number of live values and decreases
register pressure especially in cases where there are a large number
of outgoing blocks. The integer based approach is used when the
number of outgoing blocks crosses a threshold, which is currently set
to 32.

Patch by Ruiling Song.

Differential review: https://reviews.llvm.org/D127831
2022-10-31 08:58:54 -05:00

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7.3 KiB
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -unify-loop-exits -structurizecfg -S | FileCheck %s
; The structurizer uses an RPO traversal over a region, along with a
; manual hack that is meant to sort ensure that blocks within a loop
; are all visited before visiting blocks outside the loop. But this
; does not always work as expected. For example the results are
; incorrect when multiple nested loops are involved.
; The workaround for this is to unify loop exits. Each loop now
; becomes an SESE region with a single header and a single exit. The
; structurizer is a region pass, and it no longer sees the entire loop
; nest in a single region. More importantly, for each loop, the only
; block reachable outside the loop is the region exit, which avoids
; any confusion in the hacked RPO traversal.
; In the function below, B1 is an exiting block in outer loop H1. It's
; successor inside the loop is the header of another loop H2. Due to
; the incorrect traversal, B1 dominates all the blocks in the
; structurized program, except the header H1.
define void @exiting-block(i1 %PredH1, i1 %PredB2, i1 %PredB1, i1 %PredH2) {
; CHECK-LABEL: @exiting-block(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[PREDH1_INV:%.*]] = xor i1 [[PREDH1:%.*]], true
; CHECK-NEXT: [[PREDB2_INV:%.*]] = xor i1 [[PREDB2:%.*]], true
; CHECK-NEXT: br label [[H1:%.*]]
; CHECK: H1:
; CHECK-NEXT: br i1 [[PREDH1_INV]], label [[B1:%.*]], label [[FLOW3:%.*]]
; CHECK: Flow3:
; CHECK-NEXT: [[TMP0:%.*]] = phi i1 [ true, [[B1]] ], [ undef, [[H1]] ]
; CHECK-NEXT: [[TMP1:%.*]] = phi i1 [ [[PREDB1:%.*]], [[B1]] ], [ [[PREDH1]], [[H1]] ]
; CHECK-NEXT: br i1 [[TMP1]], label [[H2:%.*]], label [[FLOW4:%.*]]
; CHECK: H2:
; CHECK-NEXT: br i1 [[PREDH2:%.*]], label [[B2:%.*]], label [[FLOW:%.*]]
; CHECK: B2:
; CHECK-NEXT: br i1 [[PREDB2_INV]], label [[L2:%.*]], label [[FLOW2:%.*]]
; CHECK: Flow:
; CHECK-NEXT: [[TMP2:%.*]] = phi i1 [ false, [[FLOW2]] ], [ true, [[H2]] ]
; CHECK-NEXT: [[TMP3:%.*]] = phi i1 [ false, [[FLOW2]] ], [ undef, [[H2]] ]
; CHECK-NEXT: [[TMP4:%.*]] = phi i1 [ [[TMP7:%.*]], [[FLOW2]] ], [ true, [[H2]] ]
; CHECK-NEXT: br i1 [[TMP4]], label [[LOOP_EXIT_GUARD1:%.*]], label [[H2]]
; CHECK: L2:
; CHECK-NEXT: br label [[FLOW2]]
; CHECK: L1:
; CHECK-NEXT: br label [[FLOW5:%.*]]
; CHECK: B1:
; CHECK-NEXT: br label [[FLOW3]]
; CHECK: C:
; CHECK-NEXT: br label [[EXIT:%.*]]
; CHECK: exit:
; CHECK-NEXT: ret void
; CHECK: Flow5:
; CHECK-NEXT: [[TMP5:%.*]] = phi i1 [ undef, [[L1:%.*]] ], [ [[TMP3]], [[LOOP_EXIT_GUARD1]] ]
; CHECK-NEXT: [[TMP6:%.*]] = phi i1 [ false, [[L1]] ], [ true, [[LOOP_EXIT_GUARD1]] ]
; CHECK-NEXT: br label [[FLOW4]]
; CHECK: loop.exit.guard:
; CHECK-NEXT: br i1 [[TMP8:%.*]], label [[C:%.*]], label [[EXIT]]
; CHECK: Flow2:
; CHECK-NEXT: [[TMP7]] = phi i1 [ false, [[L2]] ], [ true, [[B2]] ]
; CHECK-NEXT: br label [[FLOW]]
; CHECK: Flow4:
; CHECK-NEXT: [[TMP8]] = phi i1 [ [[TMP5]], [[FLOW5]] ], [ [[TMP0]], [[FLOW3]] ]
; CHECK-NEXT: [[TMP9:%.*]] = phi i1 [ [[TMP6]], [[FLOW5]] ], [ true, [[FLOW3]] ]
; CHECK-NEXT: br i1 [[TMP9]], label [[LOOP_EXIT_GUARD:%.*]], label [[H1]]
; CHECK: loop.exit.guard1:
; CHECK-NEXT: br i1 [[TMP2]], label [[L1]], label [[FLOW5]]
;
entry:
br label %H1
H1: ; preds = %L1, %entry
br i1 %PredH1, label %H2, label %B1
H2: ; preds = %B1, %L2, %H1
br i1 %PredH2, label %B2, label %L1
B2: ; preds = %H2
br i1 %PredB2, label %exit, label %L2
L2: ; preds = %B2
br label %H2
L1: ; preds = %H2
br label %H1
B1: ; preds = %H1
br i1 %PredB1, label %H2, label %C
C: ; preds = %B1
br label %exit
exit: ; preds = %C, %B2
ret void
}
; The function below has three nested loops. Due to the incorrect
; traversal, H2 dominates H3 in the structurized program, and the
; backedge from L13 to H3 has no equivalent path.
define void @incorrect-backedge(i1 %PredH2, i1 %PredH3, i1 %PredL2, i1 %PredL13, i1 %PredL1)
; CHECK-LABEL: @incorrect-backedge(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[PREDH2_INV:%.*]] = xor i1 [[PREDH2:%.*]], true
; CHECK-NEXT: [[PREDL2_INV:%.*]] = xor i1 [[PREDL2:%.*]], true
; CHECK-NEXT: [[PREDH3_INV:%.*]] = xor i1 [[PREDH3:%.*]], true
; CHECK-NEXT: [[PREDL13_INV:%.*]] = xor i1 [[PREDL13:%.*]], true
; CHECK-NEXT: br label [[H1:%.*]]
; CHECK: H1:
; CHECK-NEXT: br label [[H2:%.*]]
; CHECK: H2:
; CHECK-NEXT: br i1 [[PREDH2_INV]], label [[H3:%.*]], label [[FLOW4:%.*]]
; CHECK: H3:
; CHECK-NEXT: br i1 [[PREDH3_INV]], label [[L2:%.*]], label [[FLOW:%.*]]
; CHECK: L2:
; CHECK-NEXT: br i1 [[PREDL2_INV]], label [[L13:%.*]], label [[FLOW3:%.*]]
; CHECK: Flow:
; CHECK-NEXT: [[TMP0:%.*]] = phi i1 [ [[TMP7:%.*]], [[FLOW3]] ], [ true, [[H3]] ]
; CHECK-NEXT: [[TMP1:%.*]] = phi i1 [ [[TMP8:%.*]], [[FLOW3]] ], [ false, [[H3]] ]
; CHECK-NEXT: [[TMP2:%.*]] = phi i1 [ [[TMP8]], [[FLOW3]] ], [ true, [[H3]] ]
; CHECK-NEXT: [[TMP3:%.*]] = phi i1 [ [[TMP9:%.*]], [[FLOW3]] ], [ true, [[H3]] ]
; CHECK-NEXT: br i1 [[TMP3]], label [[LOOP_EXIT_GUARD2:%.*]], label [[H3]]
; CHECK: L13:
; CHECK-NEXT: br label [[FLOW3]]
; CHECK: Flow5:
; CHECK-NEXT: [[TMP4:%.*]] = phi i1 [ [[TMP10:%.*]], [[LOOP_EXIT_GUARD1:%.*]] ], [ true, [[LOOP_EXIT_GUARD:%.*]] ]
; CHECK-NEXT: [[TMP5:%.*]] = phi i1 [ false, [[LOOP_EXIT_GUARD1]] ], [ true, [[LOOP_EXIT_GUARD]] ]
; CHECK-NEXT: br i1 [[TMP5]], label [[L1:%.*]], label [[FLOW6:%.*]]
; CHECK: L1:
; CHECK-NEXT: br label [[FLOW6]]
; CHECK: Flow6:
; CHECK-NEXT: [[TMP6:%.*]] = phi i1 [ [[PREDL1:%.*]], [[L1]] ], [ [[TMP4]], [[FLOW5:%.*]] ]
; CHECK-NEXT: br i1 [[TMP6]], label [[EXIT:%.*]], label [[H1]]
; CHECK: exit:
; CHECK-NEXT: ret void
; CHECK: loop.exit.guard:
; CHECK-NEXT: br i1 [[DOTINV:%.*]], label [[LOOP_EXIT_GUARD1]], label [[FLOW5]]
; CHECK: loop.exit.guard1:
; CHECK-NEXT: br label [[FLOW5]]
; CHECK: Flow3:
; CHECK-NEXT: [[TMP7]] = phi i1 [ true, [[L13]] ], [ false, [[L2]] ]
; CHECK-NEXT: [[TMP8]] = phi i1 [ false, [[L13]] ], [ undef, [[L2]] ]
; CHECK-NEXT: [[TMP9]] = phi i1 [ [[PREDL13_INV]], [[L13]] ], [ true, [[L2]] ]
; CHECK-NEXT: br label [[FLOW]]
; CHECK: Flow4:
; CHECK-NEXT: [[TMP10]] = phi i1 [ [[TMP2]], [[LOOP_EXIT_GUARD2]] ], [ false, [[H2]] ]
; CHECK-NEXT: [[TMP11:%.*]] = phi i1 [ [[TMP1]], [[LOOP_EXIT_GUARD2]] ], [ true, [[H2]] ]
; CHECK-NEXT: [[TMP12:%.*]] = phi i1 [ [[TMP0]], [[LOOP_EXIT_GUARD2]] ], [ true, [[H2]] ]
; CHECK-NEXT: [[DOTINV]] = xor i1 [[TMP11]], true
; CHECK-NEXT: br i1 [[TMP12]], label [[LOOP_EXIT_GUARD]], label [[H2]]
; CHECK: loop.exit.guard2:
; CHECK-NEXT: br label [[FLOW4]]
;
{
entry:
br label %H1
H1:
br label %H2
H2:
br i1 %PredH2, label %L1, label %H3
H3:
br i1 %PredH3, label %exit, label %L2
L2:
br i1 %PredL2, label %H2, label %L13
L13:
br i1 %PredL13, label %H3, label %H1
L1:
br i1 %PredL1, label %exit, label %H1
exit:
ret void
}
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