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Treat Mul just like Add and Subtract

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Like adds and subtracts, muls ripple only to the left so we can use
the same logic.

While we're here, add a print method to DemandedBits so it can be used
with -analyze, which we'll use in the testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249686 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
James Molloy 2015-10-08 12:39:59 +00:00
parent cbaa85372d
commit 6f819bd488
3 changed files with 26 additions and 1 deletions
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3
include/llvm/Analysis/DemandedBits.h
View File

@ -41,7 +41,8 @@ struct DemandedBits : public FunctionPass {
bool runOnFunction(Function& F) override;
void getAnalysisUsage(AnalysisUsage& AU) const override;
void print(raw_ostream &OS, const Module *M) const override;
/// Return the bits demanded from instruction I.
APInt getDemandedBits(Instruction *I);

12
lib/Analysis/DemandedBits.cpp
View File

@ -25,6 +25,7 @@
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h"
@ -131,6 +132,7 @@ void DemandedBits::determineLiveOperandBits(
break;
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
// Find the highest live output bit. We don't need any more input
// bits than that (adds, and thus subtracts, ripple only to the
// left).
@ -368,6 +370,16 @@ bool DemandedBits::isInstructionDead(Instruction *I) {
!isAlwaysLive(I);
}
void DemandedBits::print(raw_ostream &OS, const Module *M) const {
// This is gross. But the alternative is making all the state mutable
// just because of this one debugging method.
const_cast<DemandedBits*>(this)->performAnalysis();
for (auto &KV : AliveBits) {
OS << "DemandedBits: 0x" << utohexstr(KV.second.getLimitedValue()) << " for "
<< *KV.first << "\n";
}
}
FunctionPass *llvm::createDemandedBitsPass() {
return new DemandedBits();
}

12
test/Analysis/DemandedBits/basic.ll Normal file
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@ -0,0 +1,12 @@
; RUN: opt -S -demanded-bits -analyze < %s | FileCheck %s
; CHECK-LABEL: 'test_mul'
; CHECK-DAG: DemandedBits: 0xFF for %1 = add nsw i32 %a, 5
; CHECK-DAG: DemandedBits: 0xFF for %3 = trunc i32 %2 to i8
; CHECK-DAG: DemandedBits: 0xFF for %2 = mul nsw i32 %1, %b
define i8 @test_mul(i32 %a, i32 %b) {
%1 = add nsw i32 %a, 5
%2 = mul nsw i32 %1, %b
%3 = trunc i32 %2 to i8
ret i8 %3
}