with an additional fix to make RegAllocFast ignore undef physreg uses. It would
previously get confused about the "push %eax" instruction's use of eax. That
method for adjusting the stack pointer is used in X86FrameLowering::emitSPUpdate
as well, but since that runs after register-allocation, we didn't run into the
RegAllocFast issue before.
llvm-svn: 269949
This patch moves the expansion of WIN_ALLOCA pseudo-instructions
into a separate pass that walks the CFG and lowers the instructions
based on a conservative estimate of the offset between the stack
pointer and the lowest accessed stack address.
The goal is to reduce binary size and run-time costs by removing
calls to _chkstk. While it doesn't fix all the code quality problems
with inalloca calls, it's an incremental improvement for PR27076.
Differential Revision: http://reviews.llvm.org/D20263
llvm-svn: 269828
The size savings are significant, and from what I can tell, both ICC and GCC do this.
Differential Revision: http://reviews.llvm.org/D18573
llvm-svn: 264966
This reverts commit r262370.
It turns out there is code out there that does sequences of allocas
greater than 4K: http://crbug.com/591404
The goal of this change was to improve the code size of inalloca call
sequences, but we got tangled up in the mess of dynamic allocas.
Instead, we should come back later with a separate MI pass that uses
dominance to optimize the full sequence. This should also be able to
remove the often unneeded stacksave/stackrestore pairs around the call.
llvm-svn: 262505
The _chkstk function is called by the compiler to probe the stack in an
order consistent with Windows' expectations. However, it is possible to
elide the call to _chkstk and manually adjust the stack pointer if we
can prove that the allocation is fixed size and smaller than the probe
size.
This shrinks chrome.dll, chrome_child.dll and chrome.exe by a
cummulative ~133 KB.
Differential Revision: http://reviews.llvm.org/D17679
llvm-svn: 262370
__chkstk clobbers EAX. If EAX is live across the prologue, then we have
to take extra steps to save it. We already had code to do this if EAX
was a register parameter. This change adapts it to work when shrink
wrapping is used.
llvm-svn: 261039
Summary:
These ADJCALLSTACK markers don't generate code, but they keep dynamic
alloca code that calls chkstk out of the prologue.
This slightly pessimizes inalloca calls by preventing some register copy
coalescing, but I can live with that.
Reviewers: qcolombet
Subscribers: hans, llvm-commits
Differential Revision: http://reviews.llvm.org/D15200
llvm-svn: 254645
Hans Wennborg