http://llvm.org/bugs/show_bug.cgi?id=5276
Summary: instcombine: missed boolean simplification opportunity
Product: new-bugs
Version: unspecified
Platform: PC
OS/Version: Linux
Status: NEW
Severity: enhancement
Priority: P2
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
The code below is not simplified by instcombine:
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"
target triple = "x86_64-unknown-linux-gnu"
define i32 @foo(i32 %a, i32 %b, i32 %c) nounwind {
entry:
%tobool = icmp eq i32 %a, 0 ; <i1> [#uses=1]
%mul.mask = and i32 %b, 2147483647 ; <i32> [#uses=1]
%tobool2 = icmp eq i32 %mul.mask, 0 ; <i1> [#uses=1]
%tobool5 = icmp eq i32 %c, 0 ; <i1> [#uses=1]
%or.cond = or i1 %tobool2, %tobool5 ; <i1> [#uses=1]
%0 = xor i1 %or.cond, true ; <i1> [#uses=1]
%1 = and i1 %tobool, %0 ; <i1> [#uses=1]
br i1 %1, label %UnifiedReturnBlock, label %if.then
if.then: ; preds = %entry
%call = tail call i32 (...)* @bar() nounwind ; <i32> [#uses=0]
ret i32 5
UnifiedReturnBlock: ; preds = %entry
ret i32 4
}
However and (A, xor (or (B, C), 1)) can be transformed to
and(A, and (!B, !C)), and calculating !B and !C is easy, one just needs to flip
the predicate in the icmp.
So instcombine could see if xor(or (A,B), 1) can be transformed into and(!A,
!B)
by flipping predicates in ICMP.
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