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Disable folding loads into tail call in 32-bit PIC mode. It can introduce illegal code like this:

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addl    $12, %esp
        popl    %esi
        popl    %edi
        popl    %ebx
        popl    %ebp
        jmpl    *__Block_deallocator-L1$pb(%esi)  # TAILCALL

The problem is the global base register is assigned GR32 register class. TCRETURNmi needs the registers making up the address mode to have the GR32_TC register class.

The *proper* fix is for X86DAGToDAGISel::getGlobalBaseReg() to return a copy from the global base register of the machine function rather than returning the register itself. But that has the potential of causing it to be coalesced to a more restrictive register class: GR32_TC. It can introduce additional copies and spills. For something as important the PIC base, it's not worth it especially since this is not an issue on 64-bit.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99455 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2010-03-25 00:10:31 +00:00
parent 6a4824c466
commit cb0f06e05c
1 changed files with 5 additions and 1 deletions
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6
lib/Target/X86/X86InstrInfo.td
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@ -325,6 +325,7 @@ def FarData : Predicate<"TM.getCodeModel() != CodeModel::Small &&"
def NearData : Predicate<"TM.getCodeModel() == CodeModel::Small ||"
"TM.getCodeModel() == CodeModel::Kernel">;
def IsStatic : Predicate<"TM.getRelocationModel() == Reloc::Static">;
def IsNotPIC : Predicate<"TM.getRelocationModel() != Reloc::PIC_">;
def OptForSize : Predicate<"OptForSize">;
def OptForSpeed : Predicate<"!OptForSize">;
def FastBTMem : Predicate<"!Subtarget->isBTMemSlow()">;
@ -4346,9 +4347,12 @@ def : Pat<(X86tcret GR32_TC:$dst, imm:$off),
(TCRETURNri GR32_TC:$dst, imm:$off)>,
Requires<[In32BitMode]>;
// FIXME: This is disabled for 32-bit PIC mode because the global base
// register which is part of the address mode may be assigned a
// callee-saved register.
def : Pat<(X86tcret (load addr:$dst), imm:$off),
(TCRETURNmi addr:$dst, imm:$off)>,
Requires<[In32BitMode]>;
Requires<[In32BitMode, IsNotPIC]>;
def : Pat<(X86tcret (i32 tglobaladdr:$dst), imm:$off),
(TCRETURNdi texternalsym:$dst, imm:$off)>,