[llvm-commits] [llvm] r99455 - /llvm/trunk/lib/Target/X86/X86InstrInfo.td

[Evan Cheng]

Author: evancheng
Date: Wed Mar 24 19:10:31 2010
New Revision: 99455

URL: http://llvm.org/viewvc/llvm-project?rev=99455&view=rev
Log:
Disable folding loads into tail call in 32-bit PIC mode. It can introduce illegal code like this:

        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.

Modified:
    llvm/trunk/lib/Target/X86/X86InstrInfo.td

Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.td
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.td?rev=99455&r1=99454&r2=99455&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86InstrInfo.td (original)
+++ llvm/trunk/lib/Target/X86/X86InstrInfo.td Wed Mar 24 19:10:31 2010
@@ -325,6 +325,7 @@
 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 @@
           (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)>,