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When forgetting SCEVs for loop PHIs, don't forget SCEVUnknown values.

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These values aren't analyzable, so they don't care if more information
about the loop trip count can be had. Also, SCEVUnknown is used for
a PHI while the PHI itself is being analyzed, so it needs to be left
in the Scalars map. This fixes a variety of subtle issues.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71533 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-05-12 01:27:58 +00:00
parent 42a5875e10
commit efb9fbfdab
2 changed files with 44 additions and 2 deletions
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14
lib/Analysis/ScalarEvolution.cpp
View File

@ -2309,10 +2309,20 @@ void ScalarEvolution::forgetLoopBackedgeTakenCount(const Loop *L) {
void ScalarEvolution::forgetLoopPHIs(const Loop *L) {
BasicBlock *Header = L->getHeader();
// Push all Loop-header PHIs onto the Worklist stack, except those
// that are presently represented via a SCEVUnknown. SCEVUnknown for
// a PHI either means that it has an unrecognized structure, or it's
// a PHI that's in the progress of being computed by createNodeForPHI.
// In the former case, additional loop trip count information isn't
// going to change anything. In the later case, createNodeForPHI will
// perform the necessary updates on its own when it gets to that point.
SmallVector<Instruction *, 16> Worklist;
for (BasicBlock::iterator I = Header->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I)
Worklist.push_back(PN);
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
std::map<SCEVCallbackVH, SCEVHandle>::iterator It = Scalars.find((Value*)I);
if (It != Scalars.end() && !isa<SCEVUnknown>(It->second))
Worklist.push_back(PN);
}
while (!Worklist.empty()) {
Instruction *I = Worklist.pop_back_val();

32
test/Transforms/IndVarSimplify/loop_evaluate_5.ll Normal file
View File

@ -0,0 +1,32 @@
; RUN: llvm-as < %s | opt -indvars | llvm-dis | grep {120, %bb2.bb3_crit_edge}
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"
target triple = "i686-pc-linux-gnu"
; Indvars should be able to compute an exit value for %tmp1.
define i32 @testcase(i5 zeroext %k) nounwind readnone {
entry:
br i1 false, label %bb3, label %bb.nph
bb.nph: ; preds = %entry
br label %bb
bb: ; preds = %bb2, %bb.nph
%result2 = phi i32 [ %tmp1, %bb2 ], [ 0, %bb.nph ] ; <i32> [#uses=1]
%k_01 = phi i5 [ %indvar_next1, %bb2 ], [ 0, %bb.nph ] ; <i5> [#uses=2]
%tmp2 = zext i5 %k_01 to i32 ; <i32> [#uses=1]
%tmp1 = add i32 %tmp2, %result2 ; <i32> [#uses=2]
%indvar_next1 = add i5 %k_01, 1 ; <i5> [#uses=2]
br label %bb2
bb2: ; preds = %bb
%phitmp = icmp eq i5 %indvar_next1, -16 ; <i1> [#uses=1]
br i1 %phitmp, label %bb2.bb3_crit_edge, label %bb
bb2.bb3_crit_edge: ; preds = %bb2
br label %bb3
bb3: ; preds = %bb2.bb3_crit_edge, %entry
%result.lcssa = phi i32 [ %tmp1, %bb2.bb3_crit_edge ], [ 0, %entry ] ; <i32> [#uses=1]
ret i32 %result.lcssa
}