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InstCombine: If we call llvm.objectsize on a malloc call we can replace it with the size passed to malloc. 

llvm-svn: 122959
This commit is contained in:
Benjamin Kramer 2011-01-06 13:11:05 +00:00
parent a76cc117e0
commit 799b011276
3 changed files with 21 additions and 24 deletions
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23
llvm/lib/Target/README.txt
View File

@ -2020,29 +2020,6 @@ define i1 @g(i32 a) nounwind readnone {
//===---------------------------------------------------------------------===//
This code can be seen in viterbi:
%64 = call noalias i8* @malloc(i64 %62) nounwind
...
%67 = call i64 @llvm.objectsize.i64(i8* %64, i1 false) nounwind
%68 = call i8* @__memset_chk(i8* %64, i32 0, i64 %62, i64 %67) nounwind
llvm.objectsize.i64 should be taught about malloc/calloc, allowing it to
fold to %62. This is a security win (overflows of malloc will get caught)
and also a performance win by exposing more memsets to the optimizer.
This occurs several times in viterbi.
Stuff like this occurs in drystone:
%call5 = call i8* @malloc(i32 48) optsize
%5 = getelementptr inbounds i8* %call5, i32 16
%6 = call i32 @llvm.objectsize.i32(i8* %5, i1 false)
We should be able to constant fold that.
//===---------------------------------------------------------------------===//
This code (from Benchmarks/Dhrystone/dry.c):
define i32 @Func1(i32, i32) nounwind readnone optsize ssp {

6
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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@ -298,12 +298,16 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
}
}
} else if (CallInst *MI = extractMallocCall(Op1)) {
// Get alloca size.
// Get allocation size.
const Type* MallocType = getMallocAllocatedType(MI);
if (MallocType && MallocType->isSized())
if (Value *NElems = getMallocArraySize(MI, TD, true))
if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
Size = NElements->getZExtValue() * TD->getTypeAllocSize(MallocType);
// If there is no offset we can just return the size passed to malloc.
if (Offset == 0)
return ReplaceInstUsesWith(CI, MI->getArgOperand(0));
}
// Do not return "I don't know" here. Later optimization passes could

16
llvm/test/Transforms/InstCombine/objsize.ll
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@ -160,3 +160,19 @@ define i32 @test7() {
ret i32 %objsize
}
define i32 @test8(i32 %x) {
; CHECK: @test8
%alloc = call noalias i8* @malloc(i32 %x) nounwind
%objsize = call i32 @llvm.objectsize.i32(i8* %alloc, i1 false) nounwind readonly
; CHECK-NEXT: ret i32 %x
ret i32 %objsize
}
define i32 @test9(i32 %x) {
; CHECK: @test9
%alloc = call noalias i8* @malloc(i32 %x) nounwind
%gep = getelementptr inbounds i8* %alloc, i32 16
%objsize = call i32 @llvm.objectsize.i32(i8* %gep, i1 false) nounwind readonly
; CHECK-NOT: ret i32 %x
ret i32 %objsize
}