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clang-p2996/llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll
Roman Lebedev 371fcb720e [SimplifyCFG][PhaseOrdering] Defer lowering switch into an integer range comparison and branch until after at least the IPSCCP 
That transformation is lossy, as discussed in
https://github.com/llvm/llvm-project/issues/53853
and https://github.com/rust-lang/rust/issues/85133#issuecomment-904185574

This is an alternative to D119839,
which would add a limited IPSCCP into SimplifyCFG.

Unlike lowering switch to lookup, we still want this transformation
to happen relatively early, but after giving a chance for the things
like CVP to do their thing. It seems like deferring it just until
the IPSCCP is enough for the tests at hand, but perhaps we need to
be more aggressive and disable it until CVP.

Fixes https://github.com/llvm/llvm-project/issues/53853
Refs. https://github.com/rust-lang/rust/issues/85133

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D119854
2022-02-17 12:13:55 +03:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt %s -S -passes='simplifycfg<switch-to-lookup>' -simplifycfg-require-and-preserve-domtree=1 -switch-range-to-icmp | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
declare void @foo(i32)
define void @test(i1 %a) {
; CHECK-LABEL: @test(
; CHECK-NEXT: [[A_OFF:%.*]] = add i1 [[A:%.*]], true
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i1 [[A_OFF]], true
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: true:
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[COMMON_RET:%.*]]
; CHECK: false:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
;
switch i1 %a, label %default [i1 1, label %true
i1 0, label %false]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 2)
ret void
}
define void @test2(i2 %a) {
; CHECK-LABEL: @test2(
; CHECK-NEXT: switch i2 [[A:%.*]], label [[DOTUNREACHABLEDEFAULT:%.*]] [
; CHECK-NEXT: i2 0, label [[CASE0:%.*]]
; CHECK-NEXT: i2 1, label [[CASE1:%.*]]
; CHECK-NEXT: i2 -2, label [[CASE2:%.*]]
; CHECK-NEXT: i2 -1, label [[CASE3:%.*]]
; CHECK-NEXT: ]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: case0:
; CHECK-NEXT: call void @foo(i32 0)
; CHECK-NEXT: br label [[COMMON_RET:%.*]]
; CHECK: case1:
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[COMMON_RET]]
; CHECK: case2:
; CHECK-NEXT: call void @foo(i32 2)
; CHECK-NEXT: br label [[COMMON_RET]]
; CHECK: case3:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
; CHECK: .unreachabledefault:
; CHECK-NEXT: unreachable
;
switch i2 %a, label %default [i2 0, label %case0
i2 1, label %case1
i2 2, label %case2
i2 3, label %case3]
case0:
call void @foo(i32 0)
ret void
case1:
call void @foo(i32 1)
ret void
case2:
call void @foo(i32 2)
ret void
case3:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 4)
ret void
}
; This one is a negative test - we know the value of the default,
; but that's about it
define void @test3(i2 %a) {
; CHECK-LABEL: @test3(
; CHECK-NEXT: switch i2 [[A:%.*]], label [[DEFAULT:%.*]] [
; CHECK-NEXT: i2 0, label [[CASE0:%.*]]
; CHECK-NEXT: i2 1, label [[CASE1:%.*]]
; CHECK-NEXT: i2 -2, label [[CASE2:%.*]]
; CHECK-NEXT: ]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: case0:
; CHECK-NEXT: call void @foo(i32 0)
; CHECK-NEXT: br label [[COMMON_RET:%.*]]
; CHECK: case1:
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[COMMON_RET]]
; CHECK: case2:
; CHECK-NEXT: call void @foo(i32 2)
; CHECK-NEXT: br label [[COMMON_RET]]
; CHECK: default:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
;
switch i2 %a, label %default [i2 0, label %case0
i2 1, label %case1
i2 2, label %case2]
case0:
call void @foo(i32 0)
ret void
case1:
call void @foo(i32 1)
ret void
case2:
call void @foo(i32 2)
ret void
default:
call void @foo(i32 3)
ret void
}
; Negative test - check for possible overflow when computing
; number of possible cases.
define void @test4(i128 %a) {
; CHECK-LABEL: @test4(
; CHECK-NEXT: switch i128 [[A:%.*]], label [[DEFAULT:%.*]] [
; CHECK-NEXT: i128 0, label [[CASE0:%.*]]
; CHECK-NEXT: i128 1, label [[CASE1:%.*]]
; CHECK-NEXT: ]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: case0:
; CHECK-NEXT: call void @foo(i32 0)
; CHECK-NEXT: br label [[COMMON_RET:%.*]]
; CHECK: case1:
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[COMMON_RET]]
; CHECK: default:
; CHECK-NEXT: call void @foo(i32 2)
; CHECK-NEXT: br label [[COMMON_RET]]
;
switch i128 %a, label %default [i128 0, label %case0
i128 1, label %case1]
case0:
call void @foo(i32 0)
ret void
case1:
call void @foo(i32 1)
ret void
default:
call void @foo(i32 2)
ret void
}
; All but one bit known zero
define void @test5(i8 %a) {
; CHECK-LABEL: @test5(
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[A:%.*]], 2
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[A_OFF:%.*]] = add i8 [[A]], -1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[A_OFF]], 1
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: true:
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[COMMON_RET:%.*]]
; CHECK: false:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
;
%cmp = icmp ult i8 %a, 2
call void @llvm.assume(i1 %cmp)
switch i8 %a, label %default [i8 1, label %true
i8 0, label %false]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 2)
ret void
}
;; All but one bit known one
define void @test6(i8 %a) {
; CHECK-LABEL: @test6(
; CHECK-NEXT: [[AND:%.*]] = and i8 [[A:%.*]], -2
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[AND]], -2
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[A_OFF:%.*]] = add i8 [[A]], 1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[A_OFF]], 1
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: true:
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[COMMON_RET:%.*]]
; CHECK: false:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
;
%and = and i8 %a, 254
%cmp = icmp eq i8 %and, 254
call void @llvm.assume(i1 %cmp)
switch i8 %a, label %default [i8 255, label %true
i8 254, label %false]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 2)
ret void
}
; Check that we can eliminate both dead cases and dead defaults
; within a single run of simplifycfg
define void @test7(i8 %a) {
; CHECK-LABEL: @test7(
; CHECK-NEXT: [[AND:%.*]] = and i8 [[A:%.*]], -2
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[AND]], -2
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[A_OFF:%.*]] = add i8 [[A]], 1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[A_OFF]], 1
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: true:
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[COMMON_RET:%.*]]
; CHECK: false:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
;
%and = and i8 %a, 254
%cmp = icmp eq i8 %and, 254
call void @llvm.assume(i1 %cmp)
switch i8 %a, label %default [i8 255, label %true
i8 254, label %false
i8 0, label %also_dead]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
also_dead:
call void @foo(i32 5)
ret void
default:
call void @foo(i32 2)
ret void
}
declare void @llvm.assume(i1)
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