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[Analysis] Support bitreverse in -demanded-bits pass

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Summary:
* Add a bitreverse case in the demanded bits analysis pass.
* Add tests for the bitreverse (and bswap) intrinsic in the
  demanded bits pass.
* Add a test case to the BDCE tests: that manipulations to
  high-order bits are eliminated once the bits are reversed
  and then right-shifted.

Reviewers: mkuper, jmolloy, hfinkel, trentxintong

Reviewed By: jmolloy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31857

llvm-svn: 300215
This commit is contained in:
Brian Gesiak 2017-04-13 16:44:25 +00:00
parent ed3070c0c0
commit ee1fc77541
3 changed files with 66 additions and 0 deletions
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3
lib/Analysis/DemandedBits.cpp
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@ -110,6 +110,9 @@ void DemandedBits::determineLiveOperandBits(
// the output.
AB = AOut.byteSwap();
break;
case Intrinsic::bitreverse:
AB = AOut.reverseBits();
break;
case Intrinsic::ctlz:
if (OperandNo == 0) {
// We need some output bits, so we need all bits of the

25
test/Analysis/DemandedBits/intrinsics.ll Normal file
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@ -0,0 +1,25 @@
; RUN: opt -S -demanded-bits -analyze < %s | FileCheck %s
; RUN: opt -S -disable-output -passes="print<demanded-bits>" < %s 2>&1 | FileCheck %s
; CHECK-DAG: DemandedBits: 0xFF000000 for %1 = or i32 %x, 1
; CHECK-DAG: DemandedBits: 0xFF for %2 = call i32 @llvm.bitreverse.i32(i32 %1)
; CHECK-DAG: DemandedBits: 0xFF for %3 = trunc i32 %2 to i8
define i8 @test_bswap(i32 %x) {
%1 = or i32 %x, 1
%2 = call i32 @llvm.bswap.i32(i32 %1)
%3 = trunc i32 %2 to i8
ret i8 %3
}
declare i32 @llvm.bswap.i32(i32)
; CHECK-DAG: DemandedBits: 0xFF000000 for %1 = or i32 %x, 1
; CHECK-DAG: DemandedBits: 0xFF for %2 = call i32 @llvm.bswap.i32(i32 %1)
; CHECK-DAG: DemandedBits: 0xFF for %3 = trunc i32 %2 to i8
define i8 @test_bitreverse(i32 %x) {
%1 = or i32 %x, 1
%2 = call i32 @llvm.bitreverse.i32(i32 %1)
%3 = trunc i32 %2 to i8
ret i8 %3
}
declare i32 @llvm.bitreverse.i32(i32)

38
test/Transforms/BDCE/basic.ll
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@ -135,6 +135,44 @@ entry:
; Function Attrs: nounwind readnone
declare i32 @llvm.bswap.i32(i32) #0
; Function Attrs: nounwind readnone
define signext i32 @tim(i32 signext %x) #0 {
entry:
%call = tail call signext i32 @foo(i32 signext 5) #0
%and = and i32 %call, 536870912
%or = or i32 %and, %x
%call1 = tail call signext i32 @foo(i32 signext 3) #0
%and2 = and i32 %call1, 1073741824
%or3 = or i32 %or, %and2
%call4 = tail call signext i32 @foo(i32 signext 2) #0
%and5 = and i32 %call4, 16
%or6 = or i32 %or3, %and5
%call7 = tail call signext i32 @foo(i32 signext 1) #0
%and8 = and i32 %call7, 32
%or9 = or i32 %or6, %and8
%call10 = tail call signext i32 @foo(i32 signext 0) #0
%and11 = and i32 %call10, 64
%or12 = or i32 %or9, %and11
%call13 = tail call signext i32 @foo(i32 signext 4) #0
%and14 = and i32 %call13, 128
%or15 = or i32 %or12, %and14
%bs = tail call i32 @llvm.bitreverse.i32(i32 %or15) #0
%shr = ashr i32 %bs, 4
ret i32 %shr
; CHECK-LABEL: @tim
; CHECK-NOT: tail call signext i32 @foo(i32 signext 5)
; CHECK-NOT: tail call signext i32 @foo(i32 signext 3)
; CHECK: tail call signext i32 @foo(i32 signext 2)
; CHECK: tail call signext i32 @foo(i32 signext 1)
; CHECK: tail call signext i32 @foo(i32 signext 0)
; CHECK: tail call signext i32 @foo(i32 signext 4)
; CHECK: ret i32
}
; Function Attrs: nounwind readnone
declare i32 @llvm.bitreverse.i32(i32) #0
; Function Attrs: nounwind readnone
define signext i32 @tar2(i32 signext %x) #0 {
entry: