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llvm-mirror/test/Transforms/UnifyLoopExits/restore-ssa.ll
Sameer Sahasrabuddhe b4d5045713 Introduce unify-loop-exits pass. 
For each natural loop with multiple exit blocks, this pass creates a
new block N such that all exiting blocks now branch to N, and then
control flow is redistributed to all the original exit blocks.

The bulk of the tranformation is a new function introduced in
BasicBlockUtils that an redirect control flow from a set of incoming
blocks to a set of outgoing blocks via a common "hub".

This is a useful workaround for a limitation in the structurizer which
incorrectly orders blocks when processing a nest of loops. This pass
bypasses that issue by ensuring that each natural loop is recognized
as a separate region. Since the structurizer is a region pass, it no
longer sees a nest of loops in a single region, and instead processes
each "level" in the nesting as a separate region.

The AMDGPU backend provides a new option to enable this pass before
the structurizer, which may eventually be enabled by default.

Reviewers: madhur13490, arsenm, nhaehnle

Reviewed By: nhaehnle

Differential Revision: https://reviews.llvm.org/D75865
2020-03-30 13:23:56 -04:00

239 lines
8.3 KiB
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -unify-loop-exits -S | FileCheck %s
; Loop consists of A and B:
; - A is the header
; - A and B are exiting blocks
; - C and return are exit blocks.
; Pattern: Value (%mytmp42) defined in exiting block (A) and used in
; exit block (return).
; The relevant code uses DT::dominates(Value,
; BasicBlock). This is misnamed because it actually checks
; strict dominance, causing the pattern to be miscompiled
; (the use receives an undef value).
define i32 @exiting-used-in-exit(i32* %arg1, i32* %arg2) local_unnamed_addr align 2 {
; CHECK-LABEL: @exiting-used-in-exit(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[A:%.*]]
; CHECK: A:
; CHECK-NEXT: [[MYTMP42:%.*]] = load i32, i32* [[ARG1:%.*]], align 4
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP1]], label [[B:%.*]], label [[LOOP_EXIT_GUARD:%.*]]
; CHECK: B:
; CHECK-NEXT: [[MYTMP41:%.*]] = load i32, i32* [[ARG2:%.*]], align 4
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[MYTMP41]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[A]], label [[LOOP_EXIT_GUARD]]
; CHECK: C:
; CHECK-NEXT: [[INC:%.*]] = add i32 [[MYTMP41_MOVED:%.*]], 1
; CHECK-NEXT: br label [[RETURN:%.*]]
; CHECK: return:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ [[INC]], [[C:%.*]] ], [ [[PHI_MOVED:%.*]], [[LOOP_EXIT_GUARD]] ]
; CHECK-NEXT: ret i32 [[PHI]]
; CHECK: loop.exit.guard:
; CHECK-NEXT: [[GUARD_RETURN:%.*]] = phi i1 [ true, [[A]] ], [ false, [[B]] ]
; CHECK-NEXT: [[PHI_MOVED]] = phi i32 [ [[MYTMP42]], [[A]] ], [ undef, [[B]] ]
; CHECK-NEXT: [[MYTMP41_MOVED]] = phi i32 [ undef, [[A]] ], [ [[MYTMP41]], [[B]] ]
; CHECK-NEXT: br i1 [[GUARD_RETURN]], label [[RETURN]], label [[C]]
;
entry:
br label %A
A:
%mytmp42 = load i32, i32* %arg1, align 4
%cmp1 = icmp slt i32 %mytmp42, 0
br i1 %cmp1, label %B, label %return
B:
%mytmp41 = load i32, i32* %arg2, align 4
%cmp = icmp slt i32 %mytmp41, 0
br i1 %cmp, label %A, label %C
C:
%inc = add i32 %mytmp41, 1
br label %return
return:
%phi = phi i32 [ %inc, %C ], [ %mytmp42, %A ]
ret i32 %phi
}
; Loop consists of A, B and C:
; - A is the header
; - A and C are exiting blocks
; - B is an "internal" block that dominates exiting block C
; - D and return are exit blocks.
; Pattern: Value (%mytmp41) defined in internal block (B) and used in an
; exit block (D).
define i32 @internal-used-in-exit(i32* %arg1, i32* %arg2) local_unnamed_addr align 2 {
; CHECK-LABEL: @internal-used-in-exit(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[MYTMP42:%.*]] = load i32, i32* [[ARG1:%.*]], align 4
; CHECK-NEXT: br label [[A:%.*]]
; CHECK: A:
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP1]], label [[B:%.*]], label [[LOOP_EXIT_GUARD:%.*]]
; CHECK: B:
; CHECK-NEXT: [[MYTMP41:%.*]] = load i32, i32* [[ARG2:%.*]], align 4
; CHECK-NEXT: br label [[C:%.*]]
; CHECK: C:
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[A]], label [[LOOP_EXIT_GUARD]]
; CHECK: D:
; CHECK-NEXT: [[INC:%.*]] = add i32 [[MYTMP41_MOVED:%.*]], 1
; CHECK-NEXT: br label [[RETURN:%.*]]
; CHECK: return:
; CHECK-NEXT: ret i32 0
; CHECK: loop.exit.guard:
; CHECK-NEXT: [[GUARD_RETURN:%.*]] = phi i1 [ true, [[A]] ], [ false, [[C]] ]
; CHECK-NEXT: [[MYTMP41_MOVED]] = phi i32 [ undef, [[A]] ], [ [[MYTMP41]], [[C]] ]
; CHECK-NEXT: br i1 [[GUARD_RETURN]], label [[RETURN]], label [[D:%.*]]
;
entry:
%mytmp42 = load i32, i32* %arg1, align 4
br label %A
A:
%cmp1 = icmp slt i32 %mytmp42, 0
br i1 %cmp1, label %B, label %return
B:
%mytmp41 = load i32, i32* %arg2, align 4
br label %C
C:
%cmp = icmp slt i32 %mytmp42, 0
br i1 %cmp, label %A, label %D
D:
%inc = add i32 %mytmp41, 1
br label %return
return:
ret i32 0
}
; Loop consists of A, B and C:
; - A is the header
; - A and C are exiting blocks
; - B is an "internal" block that dominates exiting block C
; - D and return are exit blocks.
; Pattern: %return contains a phi node that receives values from
; %entry, %A and %D. This mixes all the special cases in a single phi.
define i32 @mixed-use-in-exit(i32* %arg1, i32* %arg2) local_unnamed_addr align 2 {
; CHECK-LABEL: @mixed-use-in-exit(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[MYTMP42:%.*]] = load i32, i32* [[ARG1:%.*]], align 4
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP2]], label [[A:%.*]], label [[RETURN:%.*]]
; CHECK: A:
; CHECK-NEXT: [[MYTMP43:%.*]] = add i32 [[MYTMP42]], 1
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP1]], label [[B:%.*]], label [[LOOP_EXIT_GUARD:%.*]]
; CHECK: B:
; CHECK-NEXT: [[MYTMP41:%.*]] = load i32, i32* [[ARG2:%.*]], align 4
; CHECK-NEXT: br label [[C:%.*]]
; CHECK: C:
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[A]], label [[LOOP_EXIT_GUARD]]
; CHECK: D:
; CHECK-NEXT: br label [[RETURN]]
; CHECK: return:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ [[MYTMP41_MOVED:%.*]], [[D:%.*]] ], [ [[MYTMP42]], [[ENTRY:%.*]] ], [ [[PHI_MOVED:%.*]], [[LOOP_EXIT_GUARD]] ]
; CHECK-NEXT: ret i32 [[PHI]]
; CHECK: loop.exit.guard:
; CHECK-NEXT: [[GUARD_RETURN:%.*]] = phi i1 [ true, [[A]] ], [ false, [[C]] ]
; CHECK-NEXT: [[PHI_MOVED]] = phi i32 [ [[MYTMP43]], [[A]] ], [ undef, [[C]] ]
; CHECK-NEXT: [[MYTMP41_MOVED]] = phi i32 [ undef, [[A]] ], [ [[MYTMP41]], [[C]] ]
; CHECK-NEXT: br i1 [[GUARD_RETURN]], label [[RETURN]], label [[D]]
;
entry:
%mytmp42 = load i32, i32* %arg1, align 4
%cmp2 = icmp slt i32 %mytmp42, 0
br i1 %cmp2, label %A, label %return
A:
%mytmp43 = add i32 %mytmp42, 1
%cmp1 = icmp slt i32 %mytmp42, 0
br i1 %cmp1, label %B, label %return
B:
%mytmp41 = load i32, i32* %arg2, align 4
br label %C
C:
%cmp = icmp slt i32 %mytmp42, 0
br i1 %cmp, label %A, label %D
D:
br label %return
return:
%phi = phi i32 [ %mytmp41, %D ], [ %mytmp43, %A ], [%mytmp42, %entry]
ret i32 %phi
}
; Loop consists of A, B and C:
; - A is the header
; - A and C are exiting blocks
; - B is an "internal" block that dominates exiting block C
; - D and E are exit blocks.
; Pattern: Value (%mytmp41) defined in internal block (B) and used in a
; downstream block not related to the loop (return). The use
; is a phi where the incoming block for %mytmp41 is not related
; to the loop (D).
; This pattern does not involve either the exiting blocks or
; the exit blocks, which catches any such assumptions built
; into the SSA reconstruction phase.
define i32 @phi-via-external-block(i32* %arg1, i32* %arg2) local_unnamed_addr align 2 {
; CHECK-LABEL: @phi-via-external-block(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[MYTMP42:%.*]] = load i32, i32* [[ARG1:%.*]], align 4
; CHECK-NEXT: br label [[A:%.*]]
; CHECK: A:
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP1]], label [[B:%.*]], label [[LOOP_EXIT_GUARD:%.*]]
; CHECK: B:
; CHECK-NEXT: [[MYTMP41:%.*]] = load i32, i32* [[ARG2:%.*]], align 4
; CHECK-NEXT: br label [[C:%.*]]
; CHECK: C:
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[MYTMP42]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[A]], label [[LOOP_EXIT_GUARD]]
; CHECK: D:
; CHECK-NEXT: br label [[RETURN:%.*]]
; CHECK: E:
; CHECK-NEXT: br label [[RETURN]]
; CHECK: return:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ [[MYTMP41_MOVED:%.*]], [[D:%.*]] ], [ [[MYTMP42]], [[E:%.*]] ]
; CHECK-NEXT: ret i32 [[PHI]]
; CHECK: loop.exit.guard:
; CHECK-NEXT: [[GUARD_E:%.*]] = phi i1 [ true, [[A]] ], [ false, [[C]] ]
; CHECK-NEXT: [[MYTMP41_MOVED]] = phi i32 [ undef, [[A]] ], [ [[MYTMP41]], [[C]] ]
; CHECK-NEXT: br i1 [[GUARD_E]], label [[E]], label [[D]]
;
entry:
%mytmp42 = load i32, i32* %arg1, align 4
br label %A
A:
%cmp1 = icmp slt i32 %mytmp42, 0
br i1 %cmp1, label %B, label %E
B:
%mytmp41 = load i32, i32* %arg2, align 4
br label %C
C:
%cmp = icmp slt i32 %mytmp42, 0
br i1 %cmp, label %A, label %D
D:
br label %return
E:
br label %return
return:
%phi = phi i32 [ %mytmp41, %D ], [ %mytmp42, %E ]
ret i32 %phi
}
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