https://llvm.org/bugs/show_bug.cgi?id=24670
Bug ID: 24670
Summary: Induction variable simplification does not simplify
truncates
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: san...@playingwithpointers.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Currently LLVM does not optimize `%c0` to `i1 true` in the following example:
declare void @use()
define void @f(i32 %len) {
entry:
%e = icmp slt i32 0, %len
br i1 %e, label %loop, label %leave
loop:
%idx = phi i64 [ 0, %entry ], [ %idx.inc, %be ]
%idx.inc = add i64 %idx, 1
%idx.tr = trunc i64 %idx to i32
call void @use()
%c0 = icmp slt i32 %idx.tr, %len
br i1 %c0, label %be, label %leave
be:
%idx.inc.tr = trunc i64 %idx.inc to i32
call void @use()
%c1 = icmp slt i32 %idx.inc.tr, %len
br i1 %c1, label %loop, label %leave
leave:
ret void
}
The interesting bit is that SCEV already has all the smarts required to
optimize this check away; and calling `simplifyLoopIVs` optimizes the check as
expected. -indvars does not get this case because it does not look through
truncates of induction variables, and thus does not try to eliminate `%c0`.
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