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If a global is just loaded and restored, realize that it is not changing 

value.  This allows us to turn more globals into constants and eliminate them.
This patch implements GlobalOpt/load-store-global.llx.

Note that this patch speeds up 255.vortex from:

Output/255.vortex.out-cbe.time:program 7.640000
Output/255.vortex.out-llc.time:program 9.810000

to:

Output/255.vortex.out-cbe.time:program 7.250000
Output/255.vortex.out-llc.time:program 9.490000

Which isn't bad at all!

llvm-svn: 17746
This commit is contained in:
Chris Lattner 2004-11-14 20:50:30 +00:00
parent 78d31c13ff
commit 28eeb73f2f
1 changed files with 9 additions and 3 deletions
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12
llvm/lib/Transforms/IPO/GlobalOpt.cpp
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@ -155,14 +155,20 @@ static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
// stores.
if (GS.StoredType != GlobalStatus::isStored)
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){
if (SI->getOperand(0) == GV->getInitializer()) {
Value *StoredVal = SI->getOperand(0);
if (StoredVal == GV->getInitializer()) {
if (GS.StoredType < GlobalStatus::isInitializerStored)
GS.StoredType = GlobalStatus::isInitializerStored;
} else if (isa<LoadInst>(StoredVal) &&
cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
// G = G
if (GS.StoredType < GlobalStatus::isInitializerStored)
GS.StoredType = GlobalStatus::isInitializerStored;
} else if (GS.StoredType < GlobalStatus::isStoredOnce) {
GS.StoredType = GlobalStatus::isStoredOnce;
GS.StoredOnceValue = SI->getOperand(0);
GS.StoredOnceValue = StoredVal;
} else if (GS.StoredType == GlobalStatus::isStoredOnce &&
GS.StoredOnceValue == SI->getOperand(0)) {
GS.StoredOnceValue == StoredVal) {
// noop.
} else {
GS.StoredType = GlobalStatus::isStored;