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[ARM] Make GlobalMerge merge extern globals by default

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Enabling merging of extern globals appears to be generally either beneficial or
harmless. On some benchmarks suites (on Cortex-M4F, Cortex-A9, and Cortex-A57)
it gives improvements in the 1-5% range, but in the rest the overall effect is
zero.

Differential Revision: http://reviews.llvm.org/D10966

llvm-svn: 243874
This commit is contained in:
John Brawn 2015-08-03 12:13:33 +00:00
parent bc90a464f4
commit e863b52aae
2 changed files with 55 additions and 1 deletions
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8
lib/Target/ARM/ARMTargetMachine.cpp
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@ -348,7 +348,13 @@ bool ARMPassConfig::addPreISel() {
// tricky when doing code gen per function.
bool OnlyOptimizeForSize = (TM->getOptLevel() < CodeGenOpt::Aggressive) &&
(EnableGlobalMerge == cl::BOU_UNSET);
addPass(createGlobalMergePass(TM, 127, OnlyOptimizeForSize));
// Merging of extern globals is enabled by default on non-Mach-O as we
// expect it to be generally either beneficial or harmless. On Mach-O it
// is disabled as we emit the .subsections_via_symbols directive which
// means that merging extern globals is not safe.
bool MergeExternalByDefault = !TM->getTargetTriple().isOSBinFormatMachO();
addPass(createGlobalMergePass(TM, 127, OnlyOptimizeForSize,
MergeExternalByDefault));
}
return false;

48
test/CodeGen/ARM/global-merge-external.ll Normal file
View File

@ -0,0 +1,48 @@
; RUN: llc < %s -mtriple=arm-eabi -arm-global-merge | FileCheck %s --check-prefix=CHECK-MERGE
; RUN: llc < %s -mtriple=arm-eabi -arm-global-merge -global-merge-on-external=true | FileCheck %s --check-prefix=CHECK-MERGE
; RUN: llc < %s -mtriple=arm-eabi -arm-global-merge -global-merge-on-external=false | FileCheck %s --check-prefix=CHECK-NO-MERGE
; RUN: llc < %s -mtriple=arm-macho -arm-global-merge | FileCheck %s --check-prefix=CHECK-NO-MERGE
@x = global i32 0, align 4
@y = global i32 0, align 4
@z = global i32 0, align 4
define void @f1(i32 %a1, i32 %a2) {
;CHECK: f1:
;CHECK: ldr {{r[0-9]+}}, [[LABEL1:\.LCPI[0-9]+_[0-9]]]
;CHECK: [[LABEL1]]:
;CHECK-MERGE: .long _MergedGlobals_x
;CHECK-NO-MERGE: .long {{_?x}}
store i32 %a1, i32* @x, align 4
store i32 %a2, i32* @y, align 4
ret void
}
define void @g1(i32 %a1, i32 %a2) {
;CHECK: g1:
;CHECK: ldr {{r[0-9]+}}, [[LABEL2:\.LCPI[0-9]+_[0-9]]]
;CHECK: [[LABEL2]]:
;CHECK-MERGE: .long _MergedGlobals_x
;CHECK-NO-MERGE: .long {{_?y}}
store i32 %a1, i32* @y, align 4
store i32 %a2, i32* @z, align 4
ret void
}
;CHECK-NO-MERGE-NOT: .globl _MergedGlobals_x
;CHECK-MERGE: .type _MergedGlobals_x,%object
;CHECK-MERGE: .globl _MergedGlobals_x
;CHECK-MERGE: .align 2
;CHECK-MERGE: _MergedGlobals_x:
;CHECK-MERGE: .size _MergedGlobals_x, 12
;CHECK-MERGE: .globl x
;CHECK-MERGE: x = _MergedGlobals_x
;CHECK-MERGE: .size x, 4
;CHECK-MERGE: .globl y
;CHECK-MERGE: y = _MergedGlobals_x+4
;CHECK-MERGE: .size y, 4
;CHECK-MERGE: .globl z
;CHECK-MERGE: z = _MergedGlobals_x+8
;CHECK-MERGE: .size z, 4