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indvars: insert truncate at loop boundary to avoid redundant IVs. 

When widening an IV to remove s/zext, we generally try to eliminate
the original narrow IV. However, LCSSA phi nodes outside the loop were
still using the original IV. Clean this up more aggressively to avoid
redundancy in generated code.

llvm-svn: 198338
This commit is contained in:
Andrew Trick 2014-01-02 19:29:38 +00:00
parent 4dcee6960f
commit 020dd898fc
2 changed files with 51 additions and 5 deletions
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17
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -897,15 +897,24 @@ const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) {
return AddRec;
}
/// This IV user cannot be widen. Replace this use of the original narrow IV
/// with a truncation of the new wide IV to isolate and eliminate the narrow IV.
static void truncateIVUse(NarrowIVDefUse DU, DominatorTree *DT) {
IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
}
/// WidenIVUse - Determine whether an individual user of the narrow IV can be
/// widened. If so, return the wide clone of the user.
Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
// Stop traversing the def-use chain at inner-loop phis or post-loop phis.
if (isa<PHINode>(DU.NarrowUse) &&
LI->getLoopFor(DU.NarrowUse->getParent()) != L)
LI->getLoopFor(DU.NarrowUse->getParent()) != L) {
truncateIVUse(DU, DT);
return 0;
}
// Our raison d'etre! Eliminate sign and zero extension.
if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) {
Value *NewDef = DU.WideDef;
@ -953,9 +962,7 @@ Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
// This user does not evaluate to a recurence after widening, so don't
// follow it. Instead insert a Trunc to kill off the original use,
// eventually isolating the original narrow IV so it can be removed.
IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
truncateIVUse(DU, DT);
return 0;
}
// Assume block terminators cannot evaluate to a recurrence. We can't to

39
llvm/test/Transforms/IndVarSimplify/iv-widen.ll Normal file
View File

@ -0,0 +1,39 @@
; RUN: opt < %s -indvars -S | FileCheck %s
target triple = "x86_64-apple-darwin"
; CHECK-LABEL: @sloop
; CHECK-LABEL: B18:
; Only one phi now.
; CHECK: phi
; CHECK-NOT: phi
; We now get 2 trunc, one for the gep and one for the lcssa phi.
; CHECK: trunc i64 %indvars.iv to i32
; CHECK: trunc i64 %indvars.iv to i32
; CHECK-LABEL: B24:
define void @sloop(i32* %a) {
Prologue:
br i1 undef, label %B18, label %B6
B18: ; preds = %B24, %Prologue
%.02 = phi i32 [ 0, %Prologue ], [ %tmp33, %B24 ]
%tmp23 = zext i32 %.02 to i64
%tmp33 = add i32 %.02, 1
%o = getelementptr i32* %a, i32 %.02
%v = load i32* %o
%t = icmp eq i32 %v, 0
br i1 %t, label %exit24, label %B24
B24: ; preds = %B18
%t2 = icmp eq i32 %tmp33, 20
br i1 %t2, label %B6, label %B18
B6: ; preds = %Prologue
ret void
exit24: ; preds = %B18
call void @dummy(i32 %.02)
unreachable
}
declare void @dummy(i32)