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| author | Sanjoy Das <sanjoy@playingwithpointers.com> | 2011-12-03 09:32:07 +0000 |
|---|---|---|
| committer | Sanjoy Das <sanjoy@playingwithpointers.com> | 2011-12-03 09:32:07 +0000 |
| commit | 006e43bcc0836f442057154cecc64581af4cf54a (patch) | |
| tree | 11347a2da0255cfe20812cb214b546ebbf2ced0e /llvm/lib/Target | |
| parent | 165ca1d4ba4385ab5ca1fe98976921f03e61f9cf (diff) | |
| download | bcm5719-llvm-006e43bcc0836f442057154cecc64581af4cf54a.tar.gz bcm5719-llvm-006e43bcc0836f442057154cecc64581af4cf54a.zip | |
Check for stack space more intelligently.
libgcc sets the stack limit field in TCB to 256 bytes above the actual
allocated stack limit. This means if the function's stack frame needs
less than 256 bytes, we can just compare the stack pointer with the
stack limit. This should result in lesser calls to __morestack.
llvm-svn: 145766
Diffstat (limited to 'llvm/lib/Target')
| -rw-r--r-- | llvm/lib/Target/X86/X86FrameLowering.cpp | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp index 182af84f7ca..27b762af69f 100644 --- a/llvm/lib/Target/X86/X86FrameLowering.cpp +++ b/llvm/lib/Target/X86/X86FrameLowering.cpp @@ -1306,6 +1306,10 @@ GetScratchRegister(bool Is64Bit, const MachineFunction &MF) { } } +// The stack limit in the TCB is set to this many bytes above the actual stack +// limit. +static const uint64_t kSplitStackAvailable = 256; + void X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const { MachineBasicBlock &prologueMBB = MF.front(); @@ -1360,16 +1364,24 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const { TlsReg = X86::FS; TlsOffset = 0x70; - BuildMI(checkMBB, DL, TII.get(X86::LEA64r), ScratchReg).addReg(X86::RSP) - .addImm(0).addReg(0).addImm(-StackSize).addReg(0); + if (StackSize < kSplitStackAvailable) + ScratchReg = X86::RSP; + else + BuildMI(checkMBB, DL, TII.get(X86::LEA64r), ScratchReg).addReg(X86::RSP) + .addImm(0).addReg(0).addImm(-StackSize).addReg(0); + BuildMI(checkMBB, DL, TII.get(X86::CMP64rm)).addReg(ScratchReg) .addReg(0).addImm(0).addReg(0).addImm(TlsOffset).addReg(TlsReg); } else { TlsReg = X86::GS; TlsOffset = 0x30; - BuildMI(checkMBB, DL, TII.get(X86::LEA32r), ScratchReg).addReg(X86::ESP) - .addImm(0).addReg(0).addImm(-StackSize).addReg(0); + if (StackSize < kSplitStackAvailable) + ScratchReg = X86::ESP; + else + BuildMI(checkMBB, DL, TII.get(X86::LEA32r), ScratchReg).addReg(X86::ESP) + .addImm(0).addReg(0).addImm(-StackSize).addReg(0); + BuildMI(checkMBB, DL, TII.get(X86::CMP32rm)).addReg(ScratchReg) .addReg(0).addImm(0).addReg(0).addImm(TlsOffset).addReg(TlsReg); } |
