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ARM: Align functions containing Thumb-2 jump tables to 4 bytes.

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Functions with jump tables need an alignment of 4 because they use the ADR
instruction, which aligns the PC to 4 bytes before adding an offset.

Differential Revision: http://reviews.llvm.org/D9424

llvm-svn: 236327
This commit is contained in:
Peter Collingbourne 2015-05-01 18:05:59 +00:00
parent f19a3e9172
commit daa528e28b
2 changed files with 43 additions and 0 deletions
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4
lib/Target/ARM/ARMConstantIslandPass.cpp
View File

@ -423,6 +423,10 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &mf) {
CPEMIs.clear();
DEBUG(dumpBBs());
// Functions with jump tables need an alignment of 4 because they use the ADR
// instruction, which aligns the PC to 4 bytes before adding an offset.
if (!T2JumpTables.empty())
MF->ensureAlignment(2);
/// Remove dead constant pool entries.
MadeChange |= removeUnusedCPEntries();

39
test/CodeGen/ARM/thumb-alignment.ll
View File

@ -13,3 +13,42 @@ define i32* @foo() {
define i32* @bar() {
ret i32* zeroinitializer
}
@a = external global i32
@b = external global i32
@c = external global i32
@d = external global i32
; Create a Thumb-2 jump table, which should force alignment to 4 bytes.
; CHECK: .globl baz
; CHECK-NEXT: .align 2
; CHECK: adr.w
define i32 @baz() {
%1 = load i32, i32* @c, align 4
switch i32 %1, label %7 [
i32 1, label %2
i32 4, label %5
i32 9, label %5
i32 3, label %8
]
; <label>:2
%3 = load i32, i32* @a, align 4
%4 = tail call i32 bitcast (i32 (...)* @fn2 to i32 (i32 (...)*, i32, i32)*)(i32 (...)* bitcast (i32 ()* @baz to i32 (...)*), i32 0, i32 %3) #2
br label %8
; <label>:5
%6 = load i32, i32* @d, align 4
store i32 %6, i32* @b, align 4
br label %8
; <label>:7
br label %8
; <label>:8
%e.0 = phi i32 [ 1, %7 ], [ 1, %2 ], [ 0, %0 ], [ 0, %5 ]
ret i32 %e.0
}
declare i32 @fn2(...)