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Consider only references to an IV within the loop when

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figuring out the base of the IV.  This produces better
code in the example.  (Addresses use (IV) instead of 
(BASE,IV) - a significant improvement on low-register
machines like x86).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60374 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen 2008-12-01 22:00:01 +00:00
parent c65fc3bd27
commit 589bf0865c
2 changed files with 54 additions and 6 deletions
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32
lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -643,7 +643,9 @@ void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
// cases (e.g. use of a post-incremented induction variable) the NewBase
// value will be pinned to live somewhere after the original computation.
// In this case, we have to back off.
if (!isUseOfPostIncrementedValue) {
// However, do not insert new code inside the loop when the reference
// is outside.
if (!isUseOfPostIncrementedValue && L->contains(Inst->getParent())) {
if (NewBasePt && isa<PHINode>(OperandValToReplace)) {
InsertPt = NewBasePt;
++InsertPt;
@ -921,14 +923,16 @@ static void SeparateSubExprs(std::vector<SCEVHandle> &SubExprs,
/// (a+c+d) -> (a+c). The common expression is *removed* from the Bases.
static SCEVHandle
RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses,
ScalarEvolution *SE) {
ScalarEvolution *SE, Loop *L) {
unsigned NumUses = Uses.size();
// Only one use? Use its base, regardless of what it is!
// Only one use? If inside the loop, use its base, regardless of what it is;
// if outside, use 0.
SCEVHandle Zero = SE->getIntegerSCEV(0, Uses[0].Base->getType());
SCEVHandle Result = Zero;
if (NumUses == 1) {
std::swap(Result, Uses[0].Base);
if (L->contains(Uses[0].Inst->getParent()))
std::swap(Result, Uses[0].Base);
return Result;
}
@ -941,7 +945,13 @@ RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses,
std::vector<SCEVHandle> UniqueSubExprs;
std::vector<SCEVHandle> SubExprs;
uint64_t NumUsesInsideLoop = 0;
for (unsigned i = 0; i != NumUses; ++i) {
// For this purpose, consider only uses that are inside the loop.
if (!L->contains(Uses[i].Inst->getParent()))
continue;
NumUsesInsideLoop++;
// If the base is zero (which is common), return zero now, there are no
// CSEs we can find.
if (Uses[i].Base == Zero) return Zero;
@ -961,7 +971,7 @@ RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses,
std::map<SCEVHandle, unsigned>::iterator I =
SubExpressionUseCounts.find(UniqueSubExprs[i]);
assert(I != SubExpressionUseCounts.end() && "Entry not found?");
if (I->second == NumUses) { // Found CSE!
if (I->second == NumUsesInsideLoop) { // Found CSE!
Result = SE->getAddExpr(Result, I->first);
} else {
// Remove non-cse's from SubExpressionUseCounts.
@ -974,6 +984,10 @@ RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses,
// Otherwise, remove all of the CSE's we found from each of the base values.
for (unsigned i = 0; i != NumUses; ++i) {
// For this purpose, consider only uses that are inside the loop.
if (!L->contains(Uses[i].Inst->getParent()))
continue;
// Split the expression into subexprs.
SeparateSubExprs(SubExprs, Uses[i].Base, SE);
@ -1166,7 +1180,7 @@ SCEVHandle LoopStrengthReduce::CollectIVUsers(const SCEVHandle &Stride,
// "A+B"), emit it to the preheader, then remove the expression from the
// UsersToProcess base values.
SCEVHandle CommonExprs =
RemoveCommonExpressionsFromUseBases(UsersToProcess, SE);
RemoveCommonExpressionsFromUseBases(UsersToProcess, SE, L);
// Next, figure out what we can represent in the immediate fields of
// instructions. If we can represent anything there, move it to the imm
@ -1450,6 +1464,12 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
// Add BaseV to the PHI value if needed.
RewriteExpr = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV));
// If this reference is not in the loop and we have a Common base,
// that has been added into the induction variable and must be
// subtracted off here.
if (HaveCommonExprs && !L->contains(User.Inst->getParent()))
RewriteExpr = SE->getMinusSCEV(RewriteExpr, CommonExprs);
User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt,
Rewriter, L, this,
DeadInsts);

28
test/CodeGen/X86/2008-12-01-loop-iv-used-outside-loop.ll Normal file
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@ -0,0 +1,28 @@
; RUN: llvm-as < %s | llc -mtriple=i386-apple-darwin | grep -v lea
; ModuleID = '<stdin>'
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i386-apple-darwin9.5"
define i8* @test(i8* %Q, i32* %L) nounwind {
entry:
br label %bb1
bb: ; preds = %bb1, %bb1
%indvar.next = add i32 %P.0.rec, 1 ; <i32> [#uses=1]
br label %bb1
bb1: ; preds = %bb, %entry
%P.0.rec = phi i32 [ 0, %entry ], [ %indvar.next, %bb ] ; <i32> [#uses=3]
%P.0 = getelementptr i8* %Q, i32 %P.0.rec ; <i8*> [#uses=2]
%0 = load i8* %P.0, align 1 ; <i8> [#uses=1]
switch i8 %0, label %bb3 [
i8 12, label %bb
i8 42, label %bb
]
bb3: ; preds = %bb1
%P.0.sum = add i32 %P.0.rec, 2 ; <i32> [#uses=1]
%1 = getelementptr i8* %Q, i32 %P.0.sum ; <i8*> [#uses=1]
store i8 4, i8* %1, align 1
ret i8* %P.0
}