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Don't skip over instructions other than loads that might read memory

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when trying to sink stores.

llvm-svn: 52259
This commit is contained in:
Eli Friedman 2008-06-13 22:02:12 +00:00
parent 7f1fcc4339
commit 11d4c94933
2 changed files with 25 additions and 5 deletions
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11
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -10417,18 +10417,19 @@ bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) {
return false;
break;
}
// If we find something that may be using the stored value, or if we run
// out of instructions, we can't do the xform.
if (isa<LoadInst>(BBI) || BBI->mayWriteToMemory() ||
// If we find something that may be using or overwriting the stored
// value, or if we run out of instructions, we can't do the xform.
if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() ||
BBI == OtherBB->begin())
return false;
}
// In order to eliminate the store in OtherBr, we have to
// make sure nothing reads the stored value in StoreBB.
// make sure nothing reads or overwrites the stored value in
// StoreBB.
for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
// FIXME: This should really be AA driven.
if (isa<LoadInst>(I) || I->mayWriteToMemory())
if (I->mayReadFromMemory() || I->mayWriteToMemory())
return false;
}
}

19
test/Transforms/InstCombine/2008-06-13-ReadOnlyCallStore.ll Normal file
View File

@ -0,0 +1,19 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {store i8} | count 2
define i32 @a(i8* %s) nounwind {
entry:
store i8 0, i8* %s, align 1 ; This store cannot be eliminated!
%tmp3 = call i32 @strlen( i8* %s ) nounwind readonly
%tmp5 = icmp ne i32 %tmp3, 0
br i1 %tmp5, label %bb, label %bb8
bb: ; preds = %entry
store i8 0, i8* %s, align 1
br label %bb8
bb8:
ret i32 %tmp3
}
declare i32 @strlen(i8*) nounwind readonly