[llvm-commits] [llvm] r92836 - in /llvm/trunk: lib/Target/README.txt lib/Transforms/IPO/FunctionAttrs.cpp test/Transforms/FunctionAttrs/2008-10-04-LocalMemory.ll
Duncan Sands
baldrick at free.fr
Wed Jan 6 07:37:48 PST 2010
Author: baldrick
Date: Wed Jan 6 09:37:47 2010
New Revision: 92836
URL: http://llvm.org/viewvc/llvm-project?rev=92836&view=rev
Log:
Fix a README item: have functionattrs look through selects and
phi nodes when deciding which pointers point to local memory.
I actually checked long ago how useful this is, and it isn't
very: it hardly ever fires in the testsuite, but since Chris
wants it here it is!
Modified:
llvm/trunk/lib/Target/README.txt
llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
llvm/trunk/test/Transforms/FunctionAttrs/2008-10-04-LocalMemory.ll
Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=92836&r1=92835&r2=92836&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Wed Jan 6 09:37:47 2010
@@ -1648,36 +1648,7 @@
//===---------------------------------------------------------------------===//
-FunctionAttrs is not marking this function as readnone (just readonly):
-$ clang t.c -emit-llvm -S -o - -O0 | opt -mem2reg -S -functionattrs
-
-int t(int a, int b, int c) {
- int *p;
- if (a)
- p = &a;
- else
- p = &c;
- return *p;
-}
-
-This is because we codegen this to:
-
-define i32 @t(i32 %a, i32 %b, i32 %c) nounwind readonly ssp {
-entry:
- %a.addr = alloca i32 ; <i32*> [#uses=3]
- %c.addr = alloca i32 ; <i32*> [#uses=2]
-...
-
-if.end:
- %p.0 = phi i32* [ %a.addr, %if.then ], [ %c.addr, %if.else ]
- %tmp2 = load i32* %p.0 ; <i32> [#uses=1]
- ret i32 %tmp2
-}
-
-And functionattrs doesn't realize that the p.0 load points to function local
-memory.
-
-Also, functionattrs doesn't know about memcpy/memset. This function should be
+functionattrs doesn't know much about memcpy/memset. This function should be
marked readnone rather than readonly, since it only twiddles local memory, but
functionattrs doesn't handle memset/memcpy/memmove aggressively:
Modified: llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp?rev=92836&r1=92835&r2=92836&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp Wed Jan 6 09:37:47 2010
@@ -79,16 +79,47 @@
/// memory that is local to the function. Global constants are considered
/// local to all functions.
bool FunctionAttrs::PointsToLocalMemory(Value *V) {
- V = V->getUnderlyingObject();
- // An alloca instruction defines local memory.
- if (isa<AllocaInst>(V))
- return true;
- // A global constant counts as local memory for our purposes.
- if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
- return GV->isConstant();
- // Could look through phi nodes and selects here, but it doesn't seem
- // to be useful in practice.
- return false;
+ SmallVector<Value*, 8> Worklist;
+ unsigned MaxLookup = 4;
+
+ Worklist.push_back(V);
+
+ do {
+ V = Worklist.pop_back_val()->getUnderlyingObject();
+
+ // An alloca instruction defines local memory.
+ if (isa<AllocaInst>(V))
+ continue;
+
+ // A global constant counts as local memory for our purposes.
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
+ if (!GV->isConstant())
+ return false;
+ continue;
+ }
+
+ // If both select values point to local memory, then so does the select.
+ if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
+ Worklist.push_back(SI->getTrueValue());
+ Worklist.push_back(SI->getFalseValue());
+ continue;
+ }
+
+ // If all values incoming to a phi node point to local memory, then so does
+ // the phi.
+ if (PHINode *PN = dyn_cast<PHINode>(V)) {
+ // Don't bother inspecting phi nodes with many operands.
+ if (PN->getNumIncomingValues() > MaxLookup)
+ return false;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ Worklist.push_back(PN->getIncomingValue(i));
+ continue;
+ }
+
+ return false;
+ } while (!Worklist.empty() && --MaxLookup);
+
+ return Worklist.empty();
}
/// AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
Modified: llvm/trunk/test/Transforms/FunctionAttrs/2008-10-04-LocalMemory.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/2008-10-04-LocalMemory.ll?rev=92836&r1=92835&r2=92836&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/FunctionAttrs/2008-10-04-LocalMemory.ll (original)
+++ llvm/trunk/test/Transforms/FunctionAttrs/2008-10-04-LocalMemory.ll Wed Jan 6 09:37:47 2010
@@ -1,10 +1,11 @@
-; RUN: opt < %s -functionattrs -S | grep readonly | count 3
+; RUN: opt < %s -functionattrs -S | FileCheck %s
%struct.X = type { i32*, i32* }
-declare i32 @g(i32*) readonly
+declare i32 @g(i32*) readnone
define i32 @f() {
+; CHECK: @f() readnone
%x = alloca i32 ; <i32*> [#uses=2]
store i32 0, i32* %x
%y = call i32 @g(i32* %x) ; <i32> [#uses=1]
@@ -12,6 +13,7 @@
}
define i32 @foo() nounwind {
+; CHECK: @foo() nounwind readonly
entry:
%y = alloca %struct.X ; <%struct.X*> [#uses=2]
%x = alloca %struct.X ; <%struct.X*> [#uses=2]
@@ -36,4 +38,27 @@
ret i32 %4
}
+define i32 @t(i32 %a, i32 %b, i32 %c) nounwind {
+; CHECK: @t(i32 %a, i32 %b, i32 %c) nounwind readnone
+entry:
+ %a.addr = alloca i32 ; <i32*> [#uses=3]
+ %c.addr = alloca i32 ; <i32*> [#uses=2]
+ store i32 %a, i32* %a.addr
+ store i32 %c, i32* %c.addr
+ %tmp = load i32* %a.addr ; <i32> [#uses=1]
+ %tobool = icmp ne i32 %tmp, 0 ; <i1> [#uses=1]
+ br i1 %tobool, label %if.then, label %if.else
+
+if.then: ; preds = %entry
+ br label %if.end
+
+if.else: ; preds = %entry
+ br label %if.end
+
+if.end: ; preds = %if.else, %if.then
+ %p.0 = phi i32* [ %a.addr, %if.then ], [ %c.addr, %if.else ] ; <i32*> [#uses=1]
+ %tmp2 = load i32* %p.0 ; <i32> [#uses=1]
+ ret i32 %tmp2
+}
+
declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
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