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[LSR] canonicalize Prod*(1<<C) to Prod<<C

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Summary:
Because LSR happens at a late stage where mul of a power of 2 is
typically canonicalized to shl, this canonicalization emits code that
can be better CSE'ed.

Test Plan:
Transforms/LoopStrengthReduce/shl.ll shows how this change makes GVN more
powerful. Fixes some existing tests due to this change.

Reviewers: sanjoy, majnemer, atrick

Reviewed By: majnemer, atrick

Subscribers: majnemer, llvm-commits

Differential Revision: http://reviews.llvm.org/D10448

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240573 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jingyue Wu 2015-06-24 19:28:40 +00:00
parent 1171dada02
commit 5d59315f13
6 changed files with 56 additions and 11 deletions
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17
lib/Analysis/ScalarEvolutionExpander.cpp
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@ -24,10 +24,12 @@
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
using namespace PatternMatch;
/// ReuseOrCreateCast - Arrange for there to be a cast of V to Ty at IP,
/// reusing an existing cast if a suitable one exists, moving an existing
@ -751,25 +753,30 @@ Value *SCEVExpander::visitMulExpr(const SCEVMulExpr *S) {
// out of loops.
Value *Prod = nullptr;
for (SmallVectorImpl<std::pair<const Loop *, const SCEV *> >::iterator
I = OpsAndLoops.begin(), E = OpsAndLoops.end(); I != E; ) {
I = OpsAndLoops.begin(), E = OpsAndLoops.end(); I != E; ++I) {
const SCEV *Op = I->second;
if (!Prod) {
// This is the first operand. Just expand it.
Prod = expand(Op);
++I;
} else if (Op->isAllOnesValue()) {
// Instead of doing a multiply by negative one, just do a negate.
Prod = InsertNoopCastOfTo(Prod, Ty);
Prod = InsertBinop(Instruction::Sub, Constant::getNullValue(Ty), Prod);
++I;
} else {
// A simple mul.
Value *W = expandCodeFor(Op, Ty);
Prod = InsertNoopCastOfTo(Prod, Ty);
// Canonicalize a constant to the RHS.
if (isa<Constant>(Prod)) std::swap(Prod, W);
Prod = InsertBinop(Instruction::Mul, Prod, W);
++I;
const APInt *RHS;
if (match(W, m_Power2(RHS))) {
// Canonicalize Prod*(1<<C) to Prod<<C.
assert(!Ty->isVectorTy() && "vector types are not SCEVable");
Prod = InsertBinop(Instruction::Shl, Prod,
ConstantInt::get(Ty, RHS->logBase2()));
} else {
Prod = InsertBinop(Instruction::Mul, Prod, W);
}
}
}

2
test/Transforms/LoopIdiom/basic.ll
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@ -69,7 +69,7 @@ for.end: ; preds = %for.body, %entry
ret void
; CHECK-LABEL: @test2(
; CHECK: br i1 %cmp10,
; CHECK: %0 = mul i64 %Size, 4
; CHECK: %0 = shl i64 %Size, 2
; CHECK: call void @llvm.memset.p0i8.i64(i8* %Base1, i8 1, i64 %0, i32 4, i1 false)
; CHECK-NOT: store
}

4
test/Transforms/LoopReroll/nonconst_lb.ll
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@ -52,7 +52,7 @@ for.end: ; preds = %for.body, %entry
; CHECK: %0 = add i32 %n, -1
; CHECK: %1 = sub i32 %0, %m
; CHECK: %2 = lshr i32 %1, 2
; CHECK: %3 = mul i32 %2, 4
; CHECK: %3 = shl i32 %2, 2
; CHECK: %4 = add i32 %m, %3
; CHECK: %5 = add i32 %4, 3
; CHECK: br label %for.body
@ -132,7 +132,7 @@ for.end: ; preds = %for.body, %entry
; CHECK: %0 = add i32 %n, -1
; CHECK: %1 = sub i32 %0, %rem
; CHECK: %2 = lshr i32 %1, 2
; CHECK: %3 = mul i32 %2, 4
; CHECK: %3 = shl i32 %2, 2
; CHECK: %4 = add i32 %rem, %3
; CHECK: %5 = add i32 %4, 3
; CHECK: br label %for.body

4
test/Transforms/LoopStrengthReduce/2011-10-06-ReusePhi.ll
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@ -12,8 +12,8 @@ target datalayout = "n8:16:32:64"
; CHECK-LABEL: @test(
; multiplies are hoisted out of the loop
; CHECK: while.body.lr.ph:
; CHECK: mul i64
; CHECK: mul i64
; CHECK: shl i64
; CHECK: shl i64
; GEPs are ugly
; CHECK: while.body:
; CHECK: phi

2
test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
View File

@ -6,7 +6,7 @@
; CHECK: [[r1:%[a-z0-9]+]] = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
; CHECK: [[r2:%[a-z0-9]+]] = lshr i64 [[r1]], 1
; CHECK: [[r3:%[a-z0-9]+]] = mul i64 [[r2]], 2
; CHECK: [[r3:%[a-z0-9]+]] = shl i64 [[r2]], 1
; CHECK: br label %for.body
; CHECK: for.body:
; CHECK: %lsr.iv2 = phi i64 [ %lsr.iv.next, %for.body ], [ [[r3]], %for.body.lr.ph ]

38
test/Transforms/LoopStrengthReduce/shl.ll Normal file
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@ -0,0 +1,38 @@
; RUN: opt < %s -loop-reduce -gvn -S | FileCheck %s
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
define void @_Z3fooPfll(float* nocapture readonly %input, i64 %n, i64 %s) {
; CHECK-LABEL: @_Z3fooPfll(
entry:
%mul = shl nsw i64 %s, 2
; CHECK: %mul = shl i64 %s, 2
tail call void @_Z3bazl(i64 %mul) #2
; CHECK-NEXT: call void @_Z3bazl(i64 %mul)
%cmp.5 = icmp sgt i64 %n, 0
br i1 %cmp.5, label %for.body.preheader, label %for.cond.cleanup
for.body.preheader: ; preds = %entry
br label %for.body
for.cond.cleanup.loopexit: ; preds = %for.body
br label %for.cond.cleanup
for.cond.cleanup: ; preds = %for.cond.cleanup.loopexit, %entry
ret void
for.body: ; preds = %for.body.preheader, %for.body
%i.06 = phi i64 [ %add, %for.body ], [ 0, %for.body.preheader ]
%arrayidx = getelementptr inbounds float, float* %input, i64 %i.06
; LoopStrengthReduce should reuse %mul as the stride.
; CHECK: getelementptr i1, i1* {{[^,]+}}, i64 %mul
%0 = load float, float* %arrayidx, align 4
tail call void @_Z3barf(float %0) #2
%add = add nsw i64 %i.06, %s
%cmp = icmp slt i64 %add, %n
br i1 %cmp, label %for.body, label %for.cond.cleanup.loopexit
}
declare void @_Z3bazl(i64)
declare void @_Z3barf(float)