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rewrite OptimizeAwayTrappingUsesOfLoads to 1) avoid a temporary

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vector and extraneous loop over it, 2) not delete globals used by
phis/selects etc which could actually be useful.  This fixes PR3321.
Many thanks to Duncan for narrowing this down.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62201 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-01-14 00:12:58 +00:00
parent bbdc8207d5
commit 92c6bd2c45
2 changed files with 61 additions and 24 deletions
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50
lib/Transforms/IPO/GlobalOpt.cpp
View File

@ -733,44 +733,46 @@ static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
/// if the loaded value is dynamically null, then we know that they cannot be
/// reachable with a null optimize away the load.
static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) {
std::vector<LoadInst*> Loads;
bool Changed = false;
// Keep track of whether we are able to remove all the uses of the global
// other than the store that defines it.
bool AllNonStoreUsesGone = true;
// Replace all uses of loads with uses of uses of the stored value.
for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end();
GUI != E; ++GUI)
if (LoadInst *LI = dyn_cast<LoadInst>(*GUI)) {
Loads.push_back(LI);
for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
User *GlobalUser = *GUI++;
if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
// If we were able to delete all uses of the loads
if (LI->use_empty()) {
LI->eraseFromParent();
Changed = true;
} else {
AllNonStoreUsesGone = false;
}
} else if (isa<StoreInst>(GlobalUser)) {
// Ignore the store that stores "LV" to the global.
assert(GlobalUser->getOperand(1) == GV &&
"Must be storing *to* the global");
} else {
// If we get here we could have stores, selects, or phi nodes whose values
// are loaded.
assert((isa<StoreInst>(*GUI) || isa<PHINode>(*GUI) ||
isa<SelectInst>(*GUI) || isa<ConstantExpr>(*GUI)) &&
"Only expect load and stores!");
AllNonStoreUsesGone = false;
// If we get here we could have other crazy uses that are transitively
// loaded.
assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
isa<ConstantExpr>(GlobalUser)) && "Only expect load and stores!");
}
}
if (Changed) {
DOUT << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV;
++NumGlobUses;
}
// Delete all of the loads we can, keeping track of whether we nuked them all!
bool AllLoadsGone = true;
while (!Loads.empty()) {
LoadInst *L = Loads.back();
if (L->use_empty()) {
L->eraseFromParent();
Changed = true;
} else {
AllLoadsGone = false;
}
Loads.pop_back();
}
// If we nuked all of the loads, then none of the stores are needed either,
// nor is the global.
if (AllLoadsGone) {
if (AllNonStoreUsesGone) {
DOUT << " *** GLOBAL NOW DEAD!\n";
CleanupConstantGlobalUsers(GV, 0);
if (GV->use_empty()) {

35
test/Transforms/GlobalOpt/2009-01-13-phi-user.ll Normal file
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@ -0,0 +1,35 @@
; RUN: llvm-as < %s | opt -globalopt | llvm-dis | grep {phi.*@head}
; PR3321
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-unknown-linux-gnu"
%struct.node = type { %struct.node*, i32 }
@head = internal global %struct.node* null ; <%struct.node**> [#uses=2]
@node = internal global %struct.node { %struct.node* null, i32 42 }, align 16 ; <%struct.node*> [#uses=1]
define i32 @f() nounwind {
entry:
store %struct.node* @node, %struct.node** @head, align 8
br label %bb1
bb: ; preds = %bb1
%0 = getelementptr %struct.node* %t.0, i64 0, i32 1 ; <i32*> [#uses=1]
%1 = load i32* %0, align 4 ; <i32> [#uses=1]
%2 = getelementptr %struct.node* %t.0, i64 0, i32 0 ; <%struct.node**> [#uses=1]
br label %bb1
bb1: ; preds = %bb, %entry
%value.0 = phi i32 [ undef, %entry ], [ %1, %bb ] ; <i32> [#uses=1]
%t.0.in = phi %struct.node** [ @head, %entry ], [ %2, %bb ] ; <%struct.node**> [#uses=1]
%t.0 = load %struct.node** %t.0.in ; <%struct.node*> [#uses=3]
%3 = icmp eq %struct.node* %t.0, null ; <i1> [#uses=1]
br i1 %3, label %bb2, label %bb
bb2: ; preds = %bb1
ret i32 %value.0
}
define i32 @main() nounwind {
entry:
%0 = call i32 @f() nounwind ; <i32> [#uses=1]
ret i32 %0
}