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llvm-project/llvm/test/Transforms/InstCombine/switch-shl.ll
Yingwei Zheng 1259c05122
[InstCombine] Canonicalize switch(X << C) into switch(X) (#77068) 
This patch canonicalizes `switch(X << C)` to `switch(X)`. If the shift
may wrap, an and instruction will be created to mask out all of the
shifted bits.
Alive2: https://alive2.llvm.org/ce/z/wSsL5y

NOTE: We can relax the one-use constraint. But I don't see any benefit
in my benchmark.

Compile-time impact:
http://llvm-compile-time-tracker.com/compare.php?from=a776740d6296520b8bde156aa3f8d9ecb32cddd9&to=6dd783b9f90ae5f258102d732953567d7e317c02&stat=instructions%3Au

|stage1-O3|stage1-ReleaseThinLTO|stage1-ReleaseLTO-g|stage1-O0-g|stage2-O3|stage2-O0-g|stage2-clang|
|--|--|--|--|--|--|--|
|-0.00%|+0.01%|-0.02%|-0.01%|+0.02%|-0.00%|+0.01%|
2024-01-06 01:43:21 +08:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; RUN: opt < %s -passes=instcombine -S | FileCheck %s
define i1 @test_switch_with_shl_mask(i32 %a) {
; CHECK-LABEL: define i1 @test_switch_with_shl_mask(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 [[A]] to i8
; CHECK-NEXT: switch i8 [[TRUNC]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i8 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i8 1, label [[SW_BB]]
; CHECK-NEXT: i8 -128, label [[SW_BB]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: ret i1 true
; CHECK: sw.default:
; CHECK-NEXT: ret i1 false
;
entry:
%b = shl i32 %a, 24
switch i32 %b, label %sw.default [
i32 0, label %sw.bb
i32 16777216, label %sw.bb
i32 2147483648, label %sw.bb
]
sw.bb:
ret i1 true
sw.default:
ret i1 false
}
define i1 @test_switch_with_shl_nuw_multiuse(i32 %a) {
; CHECK-LABEL: define i1 @test_switch_with_shl_nuw_multiuse(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[B:%.*]] = shl nuw i32 [[A]], 24
; CHECK-NEXT: call void @use(i32 [[B]])
; CHECK-NEXT: switch i32 [[A]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 1, label [[SW_BB]]
; CHECK-NEXT: i32 128, label [[SW_BB]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: ret i1 true
; CHECK: sw.default:
; CHECK-NEXT: ret i1 false
;
entry:
%b = shl nuw i32 %a, 24
call void @use(i32 %b)
switch i32 %b, label %sw.default [
i32 0, label %sw.bb
i32 16777216, label %sw.bb
i32 2147483648, label %sw.bb
]
sw.bb:
ret i1 true
sw.default:
ret i1 false
}
define i1 @test_switch_with_shl_nsw_multiuse(i32 %a) {
; CHECK-LABEL: define i1 @test_switch_with_shl_nsw_multiuse(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[B:%.*]] = shl nsw i32 [[A]], 24
; CHECK-NEXT: call void @use(i32 [[B]])
; CHECK-NEXT: switch i32 [[A]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 1, label [[SW_BB]]
; CHECK-NEXT: i32 -128, label [[SW_BB]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: ret i1 true
; CHECK: sw.default:
; CHECK-NEXT: ret i1 false
;
entry:
%b = shl nsw i32 %a, 24
call void @use(i32 %b)
switch i32 %b, label %sw.default [
i32 0, label %sw.bb
i32 16777216, label %sw.bb
i32 2147483648, label %sw.bb
]
sw.bb:
ret i1 true
sw.default:
ret i1 false
}
; Negative tests
define i1 @test_switch_with_shl_mask_multiuse(i32 %a) {
; CHECK-LABEL: define i1 @test_switch_with_shl_mask_multiuse(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[B:%.*]] = shl i32 [[A]], 24
; CHECK-NEXT: call void @use(i32 [[B]])
; CHECK-NEXT: switch i32 [[B]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 16777216, label [[SW_BB]]
; CHECK-NEXT: i32 -2147483648, label [[SW_BB]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: ret i1 true
; CHECK: sw.default:
; CHECK-NEXT: ret i1 false
;
entry:
%b = shl i32 %a, 24
call void @use(i32 %b)
switch i32 %b, label %sw.default [
i32 0, label %sw.bb
i32 16777216, label %sw.bb
i32 2147483648, label %sw.bb
]
sw.bb:
ret i1 true
sw.default:
ret i1 false
}
define i1 @test_switch_with_shl_mask_unknown_shamt(i32 %a, i32 %shamt) {
; CHECK-LABEL: define i1 @test_switch_with_shl_mask_unknown_shamt(
; CHECK-SAME: i32 [[A:%.*]], i32 [[SHAMT:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[B:%.*]] = shl i32 [[A]], [[SHAMT]]
; CHECK-NEXT: switch i32 [[B]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 16777216, label [[SW_BB]]
; CHECK-NEXT: i32 -2147483648, label [[SW_BB]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: ret i1 true
; CHECK: sw.default:
; CHECK-NEXT: ret i1 false
;
entry:
%b = shl i32 %a, %shamt
switch i32 %b, label %sw.default [
i32 0, label %sw.bb
i32 16777216, label %sw.bb
i32 2147483648, label %sw.bb
]
sw.bb:
ret i1 true
sw.default:
ret i1 false
}
define i1 @test_switch_with_shl_mask_poison(i32 %a) {
; CHECK-LABEL: define i1 @test_switch_with_shl_mask_poison(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: switch i32 poison, label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 0, label [[SW_BB:%.*]]
; CHECK-NEXT: i32 16777216, label [[SW_BB]]
; CHECK-NEXT: i32 -2147483648, label [[SW_BB]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: ret i1 true
; CHECK: sw.default:
; CHECK-NEXT: ret i1 false
;
entry:
%b = shl i32 %a, 32
switch i32 %b, label %sw.default [
i32 0, label %sw.bb
i32 16777216, label %sw.bb
i32 2147483648, label %sw.bb
]
sw.bb:
ret i1 true
sw.default:
ret i1 false
}
declare void @use(i32)
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