https://bugs.llvm.org/show_bug.cgi?id=34229
Bug ID: 34229
Summary: Evaluate constant condition of if statement has no
effect
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: bluechristl...@163.com
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
Simple Example:
int main()
{
int x;
if (x || 1) {}
}
Clang can not evaluate this condition and will emit IR like this:
define signext i32 @main() #0 {
entry:
%retval = alloca i32, align 4
%x = alloca i32, align 4
store i32 0, i32* %retval, align 4
%0 = load i32, i32* %x, align 4
%tobool = icmp ne i32 %0, 0
br i1 %tobool, label %if.then, label %lor.lhs.false
lor.lhs.false: ; preds = %entry
br i1 true, label %if.then, label %if.end
if.then: ; preds = %lor.lhs.false,
%entry
br label %if.end
if.end: ; preds = %if.then,
%lor.lhs.false
%1 = load i32, i32* %retval, align 4
ret i32 %1
}
However, when we swap the position of LHS and RHS, Clang can recognize it:
define signext i32 @main() #0 {
entry:
%x = alloca i32, align 4
ret i32 0
}
The same condition contains x && 0 and so on. I investigate it initially, I
find we have code to do it like code "void
DataRecursiveIntBinOpEvaluator::process(EvalResult &Result)" But seems that
there is something wrong here in if stmt condition handling.
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