https://bugs.llvm.org/show_bug.cgi?id=45210
Bug ID: 45210
Summary: Incorrect optimization of gep without inbounds + load
-> icmp eq
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Keywords: miscompilation
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: nunoplo...@sapo.pt
CC: juneyoung....@sf.snu.ac.kr, lebedev...@gmail.com,
llvm-bugs@lists.llvm.org, reg...@cs.utah.edu,
spatel+l...@rotateright.com
The following unit test in "Transforms/InstCombine/load-cmp.ll" exposes an
incorrect optimization:
define i1 @test1_noinbounds(i32 %X) {
; CHECK-LABEL: @test1_noinbounds(
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[X:%.*]], 9
; CHECK-NEXT: ret i1 [[R]]
;
%P = getelementptr [10 x i16], [10 x i16]* @G16, i32 0, i32 %X
%Q = load i16, i16* %P
%R = icmp eq i16 %Q, 0
ret i1 %R
}
Output of Alive2. TL;DR: the optimization is only correct with gep inbounds,
otherwise the transformation to "icmp eq" misses the overflow case.
@G16 = constant 20 bytes, align 16
define i1 @test1_noinbounds(i32 %X) {
#init:
store [10 x i16] { 35, 82, 69, 81, 85, 73, 82, 69, 68, 0 }, * @G16, align 16
br label %0
%0:
%P = gep * @G16, 20 x i32 0, 2 x i32 %X
%Q = load i16, * %P, align 2
%R = icmp eq i16 %Q, 0
ret i1 %R
}
=>
@G16 = constant 20 bytes, align 16
define i1 @test1_noinbounds(i32 %X) {
#init:
store [10 x i16] { 35, 82, 69, 81, 85, 73, 82, 69, 68, 0 }, * @G16, align 16
br label %0
%0:
%R = icmp eq i32 %X, 9
ret i1 %R
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
i32 %X = #x80000009 (2147483657, -2147483639)
Source:
* %P = pointer(non-local, block_id=1, offset=18)
i16 %Q = #x0000 (0)
i1 %R = #x1 (1)
Target:
i1 %R = #x0 (0)
Source value: #x1 (1)
Target value: #x0 (0)
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
