https://bugs.llvm.org/show_bug.cgi?id=34917
Bug ID: 34917
Summary: Shrink wrapping rarely fires on platforms with no
regparms (i686)
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Common Code Generator Code
Assignee: unassignedb...@nondot.org
Reporter: r...@google.com
CC: llvm-bugs@lists.llvm.org
Consider this program targetting i686-windows-msvc:
int doSomething(int*);
int /*__fastcall*/ shrink_wrap_basic(int a, int b, int c, int d) {
if (a < b)
return a;
for (int i = c; i < d; ++i)
doSomething(&c);
return doSomething(&c);
}
We can shrink wrap here successfully so long as 'a' and 'b' are passed in
ECX/EDX, i.e. when __fastcall is uncommented.
Most functions are not marked fastcall, and parameters are passed on the stack.
Shrink wrapping checks for uses of CSRs and frame indices before the split
point. However, this check is too limiting. We can probably separate fixed
frame indices for arguments from fixed frame indices in the current function's
frame by checking the offset to ensure that it is in the caller's frame.
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