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[SimplifyCFG] Don't lower complex ConstantExprs to lookup tables 

Not all ConstantExprs can be represented by a global variable, for example most
pointer arithmetic other than addition of a constant, so we can't convert these
values from switch statements to lookup tables.

Differential Revision: https://reviews.llvm.org/D25550

llvm-svn: 284379
This commit is contained in:
Oliver Stannard 2016-10-17 12:00:24 +00:00
parent 2bbec0ee7f
commit fe4432b105
2 changed files with 44 additions and 1 deletions
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5
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -4449,9 +4449,12 @@ static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI
!isa<UndefValue>(C) && !isa<ConstantExpr>(C)) !isa<UndefValue>(C) && !isa<ConstantExpr>(C))
return false; return false;
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
if (!CE->isGEPWithNoNotionalOverIndexing()) if (!CE->isGEPWithNoNotionalOverIndexing())
return false; return false;
if (!ValidLookupTableConstant(CE->getOperand(0), TTI))
return false;
}
if (!TTI.shouldBuildLookupTablesForConstant(C)) if (!TTI.shouldBuildLookupTablesForConstant(C))
return false; return false;

40
llvm/test/Transforms/SimplifyCFG/ARM/switch-to-lookup-table-constant-expr.ll Normal file
View File

@ -0,0 +1,40 @@
; RUN: opt -S -simplifycfg < %s | FileCheck %s --check-prefix=CHECK
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "armv7a--none-eabi"
; One of the phi node's values is too complex to be represented by a global
; variable, so we can't convert to a lookup table.
; CHECK-NOT: @switch.table
; CHECK-NOT: load
@g1 = external global i32, align 4
@g2 = external global i32, align 4
@g3 = external global i32, align 4
@g4 = external thread_local global i32, align 4
define i32* @test3(i32 %n) {
entry:
switch i32 %n, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb1
i32 2, label %sw.bb2
]
sw.bb:
br label %return
sw.bb1:
br label %return
sw.bb2:
br label %return
sw.default:
br label %return
return:
%retval.0 = phi i32* [ @g4, %sw.default ], [ getelementptr inbounds (i32, i32* inttoptr (i32 mul (i32 ptrtoint (i32* @g3 to i32), i32 2) to i32*), i32 1), %sw.bb2 ], [ @g2, %sw.bb1 ], [ @g1, %sw.bb ]
ret i32* %retval.0
}