http://llvm.org/bugs/show_bug.cgi?id=8014
Summary: Bottom-up FastISel broke tail calls
Product: libraries
Version: trunk
Platform: Macintosh
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: Common Code Generator Code
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
The rewrite of FastISel to go bottom-up doesn't work with tail calls. Example:
; ModuleID = '<stdin>'
target datalayout =
"e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-apple-darwin11.0"
define i32 @foo() nounwind ssp {
entry:
%0 = tail call i32 (...)* @bar() nounwind ; <i32> [#uses=1]
ret i32 %0
}
Output:
.section __TEXT,__text,regular,pure_instructions
.globl _foo
.align 4, 0x90
_foo: ## @foo
## BB#0: ## %entry
xorb %al, %al
#TC_RETURN _bar $0
movl -4(%rsp), %eax ## 4-byte Reload
ret
Formerly, lowering the tail call set the IsTailCall flag, which caused an early
exit from the loop walking instructions, which meant the ret was never
selected. emitEpilog lowered the TC_RETURN to TAILJMP, and all was well. Now,
we select the RET, which means (a) it's there in the output when it shouldn't
be, because nobody ever deletes it, and (b) emitEpilog doesn't lower the
TC_RETURN because it's not the terminator. Badness.
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