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X86: Align the stack on word boundaries in LowerFormalArguments()

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The goal of the patch is to implement section 3.2.3 of the AMD64 ABI
correctly.  The controlling sentence is, "The size of each argument gets
rounded up to eightbytes.  Therefore the stack will always be eightbyte
aligned." The equivalent sentence in the i386 ABI page 37 says, "At all
times, the stack pointer should point to a word-aligned area."  For both
architectures, the stack pointer is not being rounded up to the nearest
eightbyte or word between the last normal argument and the first
variadic argument.

Patch by Thomas Jablin!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216119 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith
2014-08-20 19:40:59 +00:00
parent ada5f2a2c7
commit 5012f1db20
3 changed files with 38 additions and 2 deletions
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9
include/llvm/CodeGen/CallingConvLower.h
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@@ -371,11 +371,16 @@ public:
return Reg;
}
/// AlignStack - Align the top of the stakc to the specified alignment.
void AlignStack(unsigned Align) {
assert(Align && ((Align - 1) & Align) == 0); // Align is power of 2.
StackOffset = ((StackOffset + Align - 1) & ~(Align - 1));
}
/// AllocateStack - Allocate a chunk of stack space with the specified size
/// and alignment.
unsigned AllocateStack(unsigned Size, unsigned Align) {
assert(Align && ((Align-1) & Align) == 0); // Align is power of 2.
StackOffset = ((StackOffset + Align-1) & ~(Align-1));
AlignStack(Align);
unsigned Result = StackOffset;
StackOffset += Size;
MF.getFrameInfo()->ensureMaxAlignment(Align);