https://bugs.llvm.org/show_bug.cgi?id=39772
Bug ID: 39772
Summary: Interprocedural Sparse Conditional Constant
Propagation generates incorrect code
Product: libraries
Version: trunk
Hardware: Macintosh
OS: MacOS X
Status: NEW
Severity: normal
Priority: P
Component: Interprocedural Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Created attachment 21148
--> https://bugs.llvm.org/attachment.cgi?id=21148&action=edit
Program that reproduces issue
The attached program generates incorrect code. Specifically, this clause:
if (left_height > right_height) {
return left_height + 1;
} else {
return right_height + 1;
}
Always returns 1 if it hits the else condition (left_height is not greater than
right_height). You can see the generated LLVM IR below. Note that, the phi node
will return 1 if it branches from %if.else:
if.end5: ; preds = %if.end
%cmp6 = icmp sgt i32 %call, %call1
br i1 %cmp6, label %if.then7, label %if.else
if.then7: ; preds = %if.end5
%add = add nsw i32 %call, 1
br label %cleanup
if.else: ; preds = %if.end5
br label %cleanup
cleanup: ; preds = %if.else,
%if.then7, %if.then
%retval.0 = phi i32 [ 0, %if.then ], [ %add, %if.then7 ], [ 1, %if.else ]
ret i32 %retval.0
}
If I add the parameter -mllvm -opt-bisect-limit=6, it still generates incorrect
code as above, bug if I change the parameter to 5, it no longer does, which
corresponds to this pass:
BISECT: running pass (6) Interprocedural Sparse Conditional Constant
Propagation on module (bug-min.c)
This behavior started some time between SVN revision 329504 and 346103. It
still happens as of 347515.
I don't think this is clang specific, but I couldn't figure out how to
reproduce with opt (I generated LLVM IR code from clang with -O0, but running
with opt -O3 did not seem to optimize anything).
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