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Module: Don't rename in getOrInsertFunction()

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During LTO, user-supplied definitions of C library functions often
exist.  -instcombine uses Module::getOrInsertFunction() to get a handle
on library functions (e.g., @puts, when optimizing @printf).

Previously, Module::getOrInsertFunction() would rename any matching
functions with local linkage, and create a new declaration.  In LTO,
this is the opposite of desired behaviour, as it skips by the
user-supplied version of the library function and creates a new
undefined reference which the linker often cannot resolve.

After some discussing with Rafael on the list, it looks like it's
undesired behaviour.  If a consumer actually *needs* this behaviour, we
should add new API with a more explicit name.

I added two testcases: one specifically for the -instcombine behaviour
and one for the LTO flow.

<rdar://problem/16165191>

llvm-svn: 203513
This commit is contained in:
Duncan P. N. Exon Smith 2014-03-10 23:42:28 +00:00
parent 9f07f16d94
commit 2635636165
3 changed files with 76 additions and 10 deletions
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10
lib/IR/Module.cpp
View File

@ -104,16 +104,6 @@ Constant *Module::getOrInsertFunction(StringRef Name,
return New; // Return the new prototype.
}
// Okay, the function exists. Does it have externally visible linkage?
if (F->hasLocalLinkage()) {
// Clear the function's name.
F->setName("");
// Retry, now there won't be a conflict.
Constant *NewF = getOrInsertFunction(Name, Ty);
F->setName(Name);
return NewF;
}
// If the function exists but has the wrong type, return a bitcast to the
// right type.
if (F->getType() != PointerType::getUnqual(Ty))

36
test/LTO/keep-used-puts-during-instcombine.ll Normal file
View File

@ -0,0 +1,36 @@
; RUN: opt -S -instcombine <%s | FileCheck %s
; rdar://problem/16165191
; llvm.compiler.used functions should not be renamed
target triple = "x86_64-apple-darwin11"
@llvm.compiler.used = appending global [1 x i8*] [
i8* bitcast (i32(i8*)* @puts to i8*)
], section "llvm.metadata"
@llvm.used = appending global [1 x i8*] [
i8* bitcast (i32(i32)* @uses_printf to i8*)
], section "llvm.metadata"
@str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
define i32 @uses_printf(i32 %i) {
entry:
%s = getelementptr [13 x i8]* @str, i64 0, i64 0
call i32 (i8*, ...)* @printf(i8* %s)
ret i32 0
}
define internal hidden i32 @printf(i8* readonly nocapture %fmt, ...) {
entry:
%ret = call i32 @bar(i8* %fmt)
ret i32 %ret
}
; CHECK: define {{.*}} @puts(
define internal hidden i32 @puts(i8* %s) {
entry:
%ret = call i32 @bar(i8* %s)
ret i32 %ret
}
declare i32 @bar(i8*)

40
test/LTO/no-undefined-puts-when-implemented.ll Normal file
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@ -0,0 +1,40 @@
; RUN: llvm-as <%s >%t1
; RUN: llvm-lto -exported-symbol=_uses_puts -exported-symbol=_uses_printf -o - %t1 | \
; RUN: llvm-nm | \
; RUN: FileCheck %s
; rdar://problem/16165191
; runtime library implementations should not be renamed
target triple = "x86_64-apple-darwin11"
@str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
; CHECK-NOT: U _puts
; CHECK: T _uses_printf
; CHECK: T _uses_puts
define i32 @uses_puts(i32 %i) {
entry:
%s = call i8* @foo(i32 %i)
%ret = call i32 @puts(i8* %s)
ret i32 %ret
}
define i32 @uses_printf(i32 %i) {
entry:
%s = getelementptr [13 x i8]* @str, i64 0, i64 0
call i32 (i8*, ...)* @printf(i8* %s)
ret i32 0
}
define hidden i32 @printf(i8* readonly nocapture %fmt, ...) {
entry:
%ret = call i32 @bar(i8* %fmt)
ret i32 %ret
}
define hidden i32 @puts(i8* %s) {
entry:
%ret = call i32 @bar(i8* %s)
ret i32 %ret
}
declare i8* @foo(i32)
declare i32 @bar(i8*)