[llvm-commits] [llvm] r122959 - in /llvm/trunk: lib/Target/README.txt lib/Transforms/InstCombine/InstCombineCalls.cpp test/Transforms/InstCombine/objsize.ll

[Nick Lewycky]

Benjamin Kramer wrote:
> Author: d0k
> Date: Thu Jan  6 07:11:05 2011
> New Revision: 122959
>
> URL: http://llvm.org/viewvc/llvm-project?rev=122959&view=rev
> Log:
> InstCombine: If we call llvm.objectsize on a malloc call we can replace it with the size passed to malloc.

Can we do anything about C++'s operator new?

Nick

> Modified:
>      llvm/trunk/lib/Target/README.txt
>      llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
>      llvm/trunk/test/Transforms/InstCombine/objsize.ll
>
> Modified: llvm/trunk/lib/Target/README.txt
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=122959&r1=122958&r2=122959&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/README.txt (original)
> +++ llvm/trunk/lib/Target/README.txt Thu Jan  6 07:11:05 2011
> @@ -2020,29 +2020,6 @@
>
>   //===---------------------------------------------------------------------===//
>
> -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 {
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=122959&r1=122958&r2=122959&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Thu Jan  6 07:11:05 2011
> @@ -298,12 +298,16 @@
>           }
>         }
>       } 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
>
> Modified: llvm/trunk/test/Transforms/InstCombine/objsize.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/objsize.ll?rev=122959&r1=122958&r2=122959&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/objsize.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/objsize.ll Thu Jan  6 07:11:05 2011
> @@ -160,3 +160,19 @@
>     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
> +}
>
>
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