[llvm] r338791 - [GlobalMerge] Allow merging globals with explicit section markings.
Eli Friedman via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 2 16:54:16 PDT 2018
Author: efriedma
Date: Thu Aug 2 16:54:16 2018
New Revision: 338791
URL: http://llvm.org/viewvc/llvm-project?rev=338791&view=rev
Log:
[GlobalMerge] Allow merging globals with explicit section markings.
At least on ELF, it's impossible to tell from the object file whether
two globals with the same section marking were merged: the merged global
uses "private" linkage to hide its symbol, and the aliases look like
regular symbols. I can't think of any other reason to disallow it.
(Of course, we can only merge globals in the same section.)
The weird alignment handling matches AsmPrinter; our alignment handling
for global variables should probably be refactored.
Differential Revision: https://reviews.llvm.org/D49822
Modified:
llvm/trunk/lib/CodeGen/GlobalMerge.cpp
llvm/trunk/test/Transforms/GlobalMerge/basic.ll
Modified: llvm/trunk/lib/CodeGen/GlobalMerge.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalMerge.cpp?rev=338791&r1=338790&r2=338791&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/GlobalMerge.cpp (original)
+++ llvm/trunk/lib/CodeGen/GlobalMerge.cpp Thu Aug 2 16:54:16 2018
@@ -461,7 +461,18 @@ bool GlobalMerge::doMerge(const SmallVec
unsigned CurIdx = 0;
for (j = i; j != -1; j = GlobalSet.find_next(j)) {
Type *Ty = Globals[j]->getValueType();
+
+ // Make sure we use the same alignment AsmPrinter would use. There
+ // currently isn't any helper to compute that, so we compute it
+ // explicitly here.
+ //
+ // getPreferredAlignment will sometimes return an alignment higher
+ // than the explicitly specified alignment; we must ignore that
+ // if the section is explicitly specified, to avoid inserting extra
+ // padding into that section.
unsigned Align = DL.getPreferredAlignment(Globals[j]);
+ if (Globals[j]->hasSection() && Globals[j]->getAlignment())
+ Align = Globals[j]->getAlignment();
unsigned Padding = alignTo(MergedSize, Align) - MergedSize;
MergedSize += Padding;
MergedSize += DL.getTypeAllocSize(Ty);
@@ -516,6 +527,7 @@ bool GlobalMerge::doMerge(const SmallVec
GlobalVariable::NotThreadLocal, AddrSpace);
MergedGV->setAlignment(MaxAlign);
+ MergedGV->setSection(Globals[i]->getSection());
const StructLayout *MergedLayout = DL.getStructLayout(MergedTy);
for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) {
@@ -599,16 +611,15 @@ bool GlobalMerge::doInitialization(Modul
IsMachO = Triple(M.getTargetTriple()).isOSBinFormatMachO();
auto &DL = M.getDataLayout();
- DenseMap<unsigned, SmallVector<GlobalVariable *, 16>> Globals, ConstGlobals,
- BSSGlobals;
+ DenseMap<std::pair<unsigned, StringRef>, SmallVector<GlobalVariable *, 16>>
+ Globals, ConstGlobals, BSSGlobals;
bool Changed = false;
setMustKeepGlobalVariables(M);
// Grab all non-const globals.
for (auto &GV : M.globals()) {
// Merge is safe for "normal" internal or external globals only
- if (GV.isDeclaration() || GV.isThreadLocal() ||
- GV.hasSection() || GV.hasImplicitSection())
+ if (GV.isDeclaration() || GV.isThreadLocal() || GV.hasImplicitSection())
continue;
// It's not safe to merge globals that may be preempted
@@ -623,6 +634,7 @@ bool GlobalMerge::doInitialization(Modul
assert(PT && "Global variable is not a pointer!");
unsigned AddressSpace = PT->getAddressSpace();
+ StringRef Section = GV.getSection();
// Ignore all 'special' globals.
if (GV.getName().startswith("llvm.") ||
@@ -637,26 +649,26 @@ bool GlobalMerge::doInitialization(Modul
if (DL.getTypeAllocSize(Ty) < MaxOffset) {
if (TM &&
TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSSLocal())
- BSSGlobals[AddressSpace].push_back(&GV);
+ BSSGlobals[{AddressSpace, Section}].push_back(&GV);
else if (GV.isConstant())
- ConstGlobals[AddressSpace].push_back(&GV);
+ ConstGlobals[{AddressSpace, Section}].push_back(&GV);
else
- Globals[AddressSpace].push_back(&GV);
+ Globals[{AddressSpace, Section}].push_back(&GV);
}
}
for (auto &P : Globals)
if (P.second.size() > 1)
- Changed |= doMerge(P.second, M, false, P.first);
+ Changed |= doMerge(P.second, M, false, P.first.first);
for (auto &P : BSSGlobals)
if (P.second.size() > 1)
- Changed |= doMerge(P.second, M, false, P.first);
+ Changed |= doMerge(P.second, M, false, P.first.first);
if (EnableGlobalMergeOnConst)
for (auto &P : ConstGlobals)
if (P.second.size() > 1)
- Changed |= doMerge(P.second, M, true, P.first);
+ Changed |= doMerge(P.second, M, true, P.first.first);
return Changed;
}
Modified: llvm/trunk/test/Transforms/GlobalMerge/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalMerge/basic.ll?rev=338791&r1=338790&r2=338791&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/GlobalMerge/basic.ll (original)
+++ llvm/trunk/test/Transforms/GlobalMerge/basic.ll Thu Aug 2 16:54:16 2018
@@ -3,18 +3,29 @@
target datalayout = "e-p:64:64"
target triple = "x86_64-unknown-linux-gnu"
-; CHECK: @_MergedGlobals = private global <{ i32, i32 }> <{ i32 1, i32 2 }>, align 4
+; CHECK: @_MergedGlobals = private global <{ i32, i32 }> <{ i32 3, i32 4 }>, section "foo", align 4
+; CHECK: @_MergedGlobals.1 = private global <{ i32, i32 }> <{ i32 1, i32 2 }>, align 4
-; CHECK: @a = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 0)
+; CHECK-DAG: @a = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals.1, i32 0, i32 0)
@a = internal global i32 1
-; CHECK: @b = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 1)
+; CHECK-DAG: @b = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals.1, i32 0, i32 1)
@b = internal global i32 2
+; CHECK-DAG: @c = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 0)
+ at c = internal global i32 3, section "foo"
+
+; CHECK-DAG: @d = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 1)
+ at d = internal global i32 4, section "foo"
+
define void @use() {
- ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 0)
+ ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals.1, i32 0, i32 0)
%x = load i32, i32* @a
- ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 1)
+ ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals.1, i32 0, i32 1)
%y = load i32, i32* @b
+ ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 0)
+ %z1 = load i32, i32* @c
+ ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 1)
+ %z2 = load i32, i32* @d
ret void
}
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