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Teach IVUsers to stop at non-affine expressions unless they are both 

outside the loop and reducible.

This more completely hides them from LSR, which isn't usually able to
do anything meaningful with non-affine expressions anyway, and this
consequently hides them from SCEVExpander, which is acutely unprepared
for non-affine expressions.

Replace test/CodeGen/X86/lsr-nonaffine.ll with a new test that tests
the new behavior.

This works around the bug in PR10117 / rdar://problem/9633149, and is
generally an improvement besides.

llvm-svn: 134268
This commit is contained in:
Dan Gohman 2011-07-01 22:05:19 +00:00
parent 51189e0b51
commit a293f24a0d
2 changed files with 35 additions and 25 deletions
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17
llvm/lib/Analysis/IVUsers.cpp
View File

@ -46,17 +46,20 @@ Pass *llvm::createIVUsersPass() {
/// used by the given expression, within the context of analyzing the
/// given loop.
static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
ScalarEvolution *SE) {
ScalarEvolution *SE, LoopInfo *LI) {
// An addrec is interesting if it's affine or if it has an interesting start.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
// Keep things simple. Don't touch loop-variant strides.
// Keep things simple. Don't touch loop-variant strides unless they're
// only used outside the loop and we can simplify them.
if (AR->getLoop() == L)
return AR->isAffine() || !L->contains(I);
return AR->isAffine() ||
(!L->contains(I) &&
SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
// Otherwise recurse to see if the start value is interesting, and that
// the step value is not interesting, since we don't yet know how to
// do effective SCEV expansions for addrecs with interesting steps.
return isInteresting(AR->getStart(), I, L, SE) &&
!isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
return isInteresting(AR->getStart(), I, L, SE, LI) &&
!isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
}
// An add is interesting if exactly one of its operands is interesting.
@ -64,7 +67,7 @@ static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
bool AnyInterestingYet = false;
for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
OI != OE; ++OI)
if (isInteresting(*OI, I, L, SE)) {
if (isInteresting(*OI, I, L, SE, LI)) {
if (AnyInterestingYet)
return false;
AnyInterestingYet = true;
@ -98,7 +101,7 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
// If we've come to an uninteresting expression, stop the traversal and
// call this a user.
if (!isInteresting(ISE, I, L, SE))
if (!isInteresting(ISE, I, L, SE, LI))
return false;
SmallPtrSet<Instruction *, 4> UniqueUsers;

43
llvm/test/CodeGen/X86/lsr-nonaffine.ll
View File

@ -1,23 +1,30 @@
; RUN: llc -march=x86-64 < %s | FileCheck %s
; RUN: llc -asm-verbose=false -march=x86-64 -o - < %s | FileCheck %s
; LSR should compute the correct starting values for this loop. Note that
; it's not necessarily LSR's job to compute loop exit expressions; that's
; indvars' job.
; CHECK: movl $12
; CHECK: movl $42
; LSR should leave non-affine expressions alone because it currently
; doesn't know how to do anything with them, and when it tries, it
; gets SCEVExpander's current expansion for them, which is suboptimal.
define i32 @real_symmetric_eigen(i32 %n) nounwind {
while.body127: ; preds = %while.cond122
br label %while.cond141
; CHECK: xorl %eax, %eax
; CHECK-NEXT: align
; CHECK-NEXT: BB0_1:
; CHECK-NEXT: movq %rax, (%rdx)
; CHECK-NEXT: addq %rsi, %rax
; CHECK-NEXT: cmpq %rdi, %rax
; CHECK-NEXT: jl
; CHECK-NEXT: imulq %rax, %rax
; CHECK-NEXT: ret
define i64 @foo(i64 %n, i64 %s, i64* %p) nounwind {
entry:
br label %loop
while.cond141: ; preds = %while.cond141, %while.body127
%0 = phi i32 [ 7, %while.body127 ], [ %indvar.next67, %while.cond141 ] ; <i32> [#uses=3]
%indvar.next67 = add i32 %0, 1 ; <i32> [#uses=1]
%t = icmp slt i32 %indvar.next67, %n
br i1 %t, label %if.then171, label %while.cond141
loop:
%i = phi i64 [ 0, %entry ], [ %i.next, %loop ]
volatile store i64 %i, i64* %p
%i.next = add i64 %i, %s
%c = icmp slt i64 %i.next, %n
br i1 %c, label %loop, label %exit
if.then171: ; preds = %while.cond141
%mul150 = mul i32 %0, %0 ; <i32> [#uses=1]
%add174 = add i32 %mul150, %0 ; <i32> [#uses=1]
ret i32 %add174
exit:
%mul = mul i64 %i.next, %i.next
ret i64 %mul
}