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Let FuncAttrs infer the 'returned' argument attribute

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A function can have one argument with the 'returned' attribute, indicating that
the associated argument is always the return value of the function. Add
FuncAttrs inference logic.

Differential Revision: http://reviews.llvm.org/D22202

llvm-svn: 275027
This commit is contained in:
Hal Finkel 2016-07-10 22:02:55 +00:00
parent f6aeef6f80
commit 6271874a51
4 changed files with 48 additions and 6 deletions
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42
lib/Transforms/IPO/FunctionAttrs.cpp
View File

@ -42,6 +42,7 @@ using namespace llvm;
STATISTIC(NumReadNone, "Number of functions marked readnone");
STATISTIC(NumReadOnly, "Number of functions marked readonly");
STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
STATISTIC(NumReturned, "Number of arguments marked returned");
STATISTIC(NumReadNoneArg, "Number of arguments marked readnone");
STATISTIC(NumReadOnlyArg, "Number of arguments marked readonly");
STATISTIC(NumNoAlias, "Number of function returns marked noalias");
@ -483,6 +484,45 @@ determinePointerReadAttrs(Argument *A,
return IsRead ? Attribute::ReadOnly : Attribute::ReadNone;
}
/// Deduce returned attributes for the SCC.
static bool addArgumentReturnedAttrs(const SCCNodeSet &SCCNodes) {
bool Changed = false;
AttrBuilder B;
B.addAttribute(Attribute::Returned);
// Check each function in turn, determining if an argument is always returned.
for (Function *F : SCCNodes) {
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
continue;
if (F->getReturnType()->isVoidTy())
continue;
SmallPtrSet<Value *, 2> RetArgs;
for (BasicBlock &BB : *F)
if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator())) {
// Note that stripPointerCasts should look through functions with
// returned arguments.
Value *RetVal = Ret->getReturnValue()->stripPointerCasts();
if (RetVal->getType() == F->getReturnType() && isa<Argument>(RetVal))
RetArgs.insert(RetVal);
}
if (RetArgs.size() == 1) {
auto *A = cast<Argument>(*RetArgs.begin());
A->addAttr(AttributeSet::get(F->getContext(), A->getArgNo() + 1, B));
++NumReturned;
Changed = true;
}
}
return Changed;
}
/// Deduce nocapture attributes for the SCC.
static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
bool Changed = false;
@ -1024,6 +1064,7 @@ PreservedAnalyses PostOrderFunctionAttrsPass::run(LazyCallGraph::SCC &C,
}
bool Changed = false;
Changed |= addArgumentReturnedAttrs(SCCNodes);
Changed |= addReadAttrs(SCCNodes, AARGetter);
Changed |= addArgumentAttrs(SCCNodes);
@ -1089,6 +1130,7 @@ static bool runImpl(CallGraphSCC &SCC, AARGetterT AARGetter) {
SCCNodes.insert(F);
}
Changed |= addArgumentReturnedAttrs(SCCNodes);
Changed |= addReadAttrs(SCCNodes, AARGetter);
Changed |= addArgumentAttrs(SCCNodes);

2
test/Transforms/FunctionAttrs/2009-01-02-LocalStores.ll
View File

@ -14,7 +14,7 @@ define i32* @b(i32 *%q) {
ret i32* %tmp
}
; CHECK: define i32* @c(i32* readnone %r)
; CHECK: define i32* @c(i32* readnone returned %r)
@g = global i32 0
define i32* @c(i32 *%r) {
%a = icmp eq i32* %r, null

6
test/Transforms/FunctionAttrs/nocapture.ll
View File

@ -1,7 +1,7 @@
; RUN: opt < %s -functionattrs -S | FileCheck %s
@g = global i32* null ; <i32**> [#uses=1]
; CHECK: define i32* @c1(i32* readnone %q)
; CHECK: define i32* @c1(i32* readnone returned %q)
define i32* @c1(i32* %q) {
ret i32* %q
}
@ -140,7 +140,7 @@ define void @test1_1(i8* %x1_1, i8* %y1_1) {
ret void
}
; CHECK: define i8* @test1_2(i8* nocapture readnone %x1_2, i8* %y1_2)
; CHECK: define i8* @test1_2(i8* nocapture readnone %x1_2, i8* returned %y1_2)
define i8* @test1_2(i8* %x1_2, i8* %y1_2) {
call void @test1_1(i8* %x1_2, i8* %y1_2)
store i32* null, i32** @g
@ -168,7 +168,7 @@ define void @test4_1(i8* %x4_1) {
ret void
}
; CHECK: define i8* @test4_2(i8* nocapture readnone %x4_2, i8* readnone %y4_2, i8* nocapture readnone %z4_2)
; CHECK: define i8* @test4_2(i8* nocapture readnone %x4_2, i8* readnone returned %y4_2, i8* nocapture readnone %z4_2)
define i8* @test4_2(i8* %x4_2, i8* %y4_2, i8* %z4_2) {
call void @test4_1(i8* null)
store i32* null, i32** @g

4
test/Transforms/FunctionAttrs/readattrs.ll
View File

@ -11,7 +11,7 @@ define void @test1_2(i8* %x1_2, i8* %y1_2, i8* %z1_2) {
ret void
}
; CHECK: define i8* @test2(i8* readnone %p)
; CHECK: define i8* @test2(i8* readnone returned %p)
define i8* @test2(i8* %p) {
store i32 0, i32* @x
ret i8* %p
@ -53,7 +53,7 @@ define void @test7_1(i32* inalloca %a) {
ret void
}
; CHECK: define i32* @test8_1(i32* readnone %p)
; CHECK: define i32* @test8_1(i32* readnone returned %p)
define i32* @test8_1(i32* %p) {
entry:
ret i32* %p