[PATCH] D71617: [WIP][NFC][Attributor] noalias attribute deduction fixme

[pankaj gode via Phabricator via llvm-commits]

pgode added a comment.

In D71617#1911979 <https://reviews.llvm.org/D71617#1911979>, @jdoerfert wrote:

> @pgode Are you still looking into this? Do you need feedback from me?


I apologize for not coming back on this as I got tied up with other tasks.

Thank you for patiently clarifying things so far. 
I agree to the changes which you suggested but I couldn't create a new test which passes due to this change.

As you had pointed that I was not clear in my logic. Major reason for that was I had incomplete understanding of fixpoint iteration and data flow analysis concepts, which I could get a better understanding now.
Please guide me more on examples or if you think I should work on something else if there is better solution with someone.

Bit more detail on the examples (I am referring) are:

1. I started with wrong example. In the code below, I was questioning noalias attribute propagation to strtox. Here the log message clearly showed that the pointer 's' gets captured by 'sh_fromstring' callsite in strtox.

  ; Function Attrs: nounwind optsize define dso_local float @strtof(i8* noalias %s, i8** noalias %p) #0 { entry: %call = tail call fastcc double @strtox(i8* %s, i8** %p, i32 0) #3 %conv = fptrunc double %call to float ret float %conv }

  ; Function Attrs: nounwind optsize define internal fastcc double @strtox(i8* %s, i8** %p, i32 %prec) unnamed_addr #0 { entry: %f = alloca %struct._IO_FILE, align 8 %0 = bitcast %struct._IO_FILE* %f to i8* call void @llvm.lifetime.start.p0i8(i64 144, i8* nonnull %0) #4 %call = call i32 bitcast (i32 (...)* @sh_fromstring to i32 (%struct._IO_FILE*, i8*)*)(%struct._IO_FILE* nonnull %f, i8* %s) #5 call void @__shlim(%struct._IO_FILE* nonnull %f, i64 0) #5 %call1 = call double @__floatscan(%struct._IO_FILE* nonnull %f, i32 %prec, i32 1) #5 %shcnt = getelementptr inbounds %struct._IO_FILE, %struct._IO_FILE* %f, i32 0, i32 30 %1 = load i64, i64* %shcnt, align 8, !tbaa !2 ... } ; Function Attrs: nounwind optsize define dso_local double @strtold(i8* noalias %s, i8** noalias %p) #0 { entry: %call = tail call fastcc double @strtox(i8* %s, i8** %p, i32 2) #3 ret double %call }

2. In the other example as well I got it wrong when I was questioning that the noalias attribute should propagate callsite argument %a to test10_helper_1(). This can't happen because the test10_helper_1 is not defined thus we can't determine noalias correctly even though test10_helper_1 callsite is reachable.

TEST 10
declare void @test10_helper_1(i8* %a)
define void @test10_helper_2(i8* noalias %a) {

  tail call void @test10_helper_1(i8* %a)
  ret void

}
define void @test10(i8* noalias %a) {

  tail call void @test10_helper_1(i8* %a)
  tail call void @test10_helper_2(i8* %a)
  ret void

}


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