http://llvm.org/bugs/show_bug.cgi?id=4413
Summary: Missed optimization in select on correlated phi nodes
Product: libraries
Version: trunk
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: Scalar Optimizations
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Created an attachment (id=3102)
--> (http://llvm.org/bugs/attachment.cgi?id=3102)
Assembly with missed optimization.
`opt -O3` at head fails to optimize the following function:
declare i32 @ext()
define i32 @foo(i1 %a) {
entry:
br i1 %a, label %bb1, label %bb2
bb1: ; preds = %entry
%0 = tail call i32 @ext() ; <i32> [#uses=1]
br label %bb2
bb2: ; preds = %bb1, %entry
%cond = phi i1 [ true, %bb1 ], [ false, %entry ] ; <i1>
[#uses=1]
%val = phi i32 [ %0, %bb1 ], [ 0, %entry ] ; <i32>
[#uses=1]
%res = select i1 %cond, i32 %val, i32 0 ; <i32> [#uses=1]
ret i32 %res
}
Despite the fact that %res is equal to %val for every in-edge to %bb2, so the
select could be removed.
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