[llvm] r332813 - [GlobalMerge] Exit early if only one global is to be merged

[Haicheng Wu via llvm-commits]

Author: haicheng
Date: Sat May 19 11:00:02 2018
New Revision: 332813

URL: http://llvm.org/viewvc/llvm-project?rev=332813&view=rev
Log:
[GlobalMerge] Exit early if only one global is to be merged

To save some compilation time and prevent some unnecessary changes.

Differential Revision: https://reviews.llvm.org/D46640

Modified:
    llvm/trunk/lib/CodeGen/GlobalMerge.cpp
    llvm/trunk/test/CodeGen/AArch64/global-merge-3.ll
    llvm/trunk/test/CodeGen/ARM/global-merge.ll

Modified: llvm/trunk/lib/CodeGen/GlobalMerge.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalMerge.cpp?rev=332813&r1=332812&r2=332813&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/GlobalMerge.cpp (original)
+++ llvm/trunk/lib/CodeGen/GlobalMerge.cpp Sat May 19 11:00:02 2018
@@ -445,6 +445,7 @@ bool GlobalMerge::doMerge(const SmallVec
   LLVM_DEBUG(dbgs() << " Trying to merge set, starts with #"
                     << GlobalSet.find_first() << "\n");
 
+  bool Changed = false;
   ssize_t i = GlobalSet.find_first();
   while (i != -1) {
     ssize_t j = 0;
@@ -469,6 +470,12 @@ bool GlobalMerge::doMerge(const SmallVec
       }
     }
 
+    // Exit early if there is only one global to merge.
+    if (Tys.size() < 2) {
+      i = j;
+      continue;
+    }
+
     // If merged variables doesn't have external linkage, we needn't to expose
     // the symbol after merging.
     GlobalValue::LinkageTypes Linkage = HasExternal
@@ -526,10 +533,11 @@ bool GlobalMerge::doMerge(const SmallVec
 
       NumMerged++;
     }
+    Changed = true;
     i = j;
   }
 
-  return true;
+  return Changed;
 }
 
 void GlobalMerge::collectUsedGlobalVariables(Module &M) {

Modified: llvm/trunk/test/CodeGen/AArch64/global-merge-3.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/global-merge-3.ll?rev=332813&r1=332812&r2=332813&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/global-merge-3.ll (original)
+++ llvm/trunk/test/CodeGen/AArch64/global-merge-3.ll Sat May 19 11:00:02 2018
@@ -10,8 +10,8 @@ define void @f1(i32 %a1, i32 %a2, i32 %a
 ;CHECK-APPLE-IOS: adrp	x8, __MergedGlobals_x at PAGE
 ;CHECK-APPLE-IOS-NOT: adrp
 ;CHECK-APPLE-IOS: add	x8, x8, __MergedGlobals_x at PAGEOFF
-;CHECK-APPLE-IOS: adrp	x9, __MergedGlobals_y at PAGE+12
-;CHECK-APPLE-IOS: str	w1, [x9, __MergedGlobals_y at PAGEOFF+12]
+;CHECK-APPLE-IOS: adrp	x9, _y at PAGE+12
+;CHECK-APPLE-IOS: str	w1, [x9]
   %x3 = getelementptr inbounds [1000 x i32], [1000 x i32]* @x, i32 0, i64 3
   %y3 = getelementptr inbounds [1000 x i32], [1000 x i32]* @y, i32 0, i64 3
   store i32 %a1, i32* %x3, align 4
@@ -25,27 +25,19 @@ define void @f1(i32 %a1, i32 %a2, i32 %a
 ;CHECK: .L_MergedGlobals:
 ;CHECK: .size	.L_MergedGlobals, 4004
 
-;CHECK: .type	.L_MergedGlobals.1, at object // @_MergedGlobals.1
-;CHECK: .local	.L_MergedGlobals.1
-;CHECK: .comm	.L_MergedGlobals.1,4000,16
+;CHECK-APPLE-IOS: .zerofill __DATA,__common,_y,4000,2
 
 ;CHECK-APPLE-IOS: .p2align	4
 ;CHECK-APPLE-IOS:  __MergedGlobals_x:
 ;CHECK-APPLE-IOS: .long 1
 ;CHECK-APPLE-IOS: .space	4000
 
-;CHECK-APPLE-IOS: .zerofill __DATA,__common,__MergedGlobals_y,4000,4
 
 ;CHECK: .set z, .L_MergedGlobals
 ;CHECK:	.globl	x
 ;CHECK: .set x, .L_MergedGlobals+4
 ;CHECK: .size x, 4000
-;CHECK:	.globl	y
-;CHECK: .set y, .L_MergedGlobals.1
-;CHECK: .size y, 4000
 
 ;CHECK-APPLE-IOS-NOT: .set _z, __MergedGlobals_x
 ;CHECK-APPLE-IOS:.globl	_x
 ;CHECK-APPLE-IOS:.set _x, __MergedGlobals_x+4
-;CHECK-APPLE-IOS:.globl	_y
-;CHECK-APPLE-IOS:.set _y, __MergedGlobals_y

Modified: llvm/trunk/test/CodeGen/ARM/global-merge.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/global-merge.ll?rev=332813&r1=332812&r2=332813&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/global-merge.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/global-merge.ll Sat May 19 11:00:02 2018
@@ -52,23 +52,23 @@ declare i8* @__cxa_begin_catch(i8*)
 
 declare void @__cxa_end_catch()
 
+; CHECK: g3:
 ; CHECK: _MergedGlobals:
 @g1 = internal global i32 1
 @g2 = internal global i32 2
 
 ; Make sure that the complete variable fits within the range of the maximum
 ; offset.  Having the starting offset in range is not sufficient.
-; When this works properly, @g3 is placed in a separate chunk of merged globals.
-; CHECK: _MergedGlobals.1:
+; When this works properly, @g3 is not merged.
 @g3 = internal global [30 x i32] [ i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10 ], align 4
 
 ; Global variables that can be placed in BSS should be kept together in a
 ; separate pool of merged globals.
-; CHECK: _MergedGlobals.2
+; CHECK: _MergedGlobals.1
 @g4 = internal global i32 0
 @g5 = internal global i32 0
 
 ; Global variables that are constant can be merged together
-; CHECK: _MergedGlobals.3
+; CHECK: _MergedGlobals.2
 @g6 = internal constant [12 x i32] zeroinitializer, align 4
 @g7 = internal constant [12 x i32] zeroinitializer, align 4