https://llvm.org/bugs/show_bug.cgi?id=23345
Bug ID: 23345
Summary: [globalsmodref-aa] Atomics not considered to access
memory.
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: release blocker
Priority: P
Component: Global Analyses
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
The loop "// Scan the function bodies for explicit loads or stores." in
http://llvm.org/klaus/llvm/blob/master/lib/Analysis/IPA/GlobalsModRef.cpp#L-438
appears to ignore atomic operations (e.g. cmpxchg, atomicrmw).
Patch will be on llvm-commits shortly.
This bug has probably been latent since those instructions were introduced. A
quick blame shows the loop was last touched in 2012.
I found this because the "compare and swap" was being hoisted out of a standard
"compare and swap" loop with -fno-inline:
test case:
opt -S <test2.ll -globalsmodref-aa -licm
test2.ll:
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.10.0"
define i32 @_Z1fPx(i64* %p) {
br label %1
; <label>:1 ; preds = %1, %0
%2 = call i64 @_ZL16compareAndSwap64Pxxx(i64* %p)
%3 = icmp eq i64 %2, 0
br i1 %3, label %1, label %4
; <label>:4 ; preds = %1
ret i32 3
}
define internal i64 @_ZL16compareAndSwap64Pxxx(i64* %ptr) nounwind {
%1 = cmpxchg i64* %ptr, i64 0, i64 -1 monotonic monotonic
%2 = extractvalue { i64, i1 } %1, 1
%3 = extractvalue { i64, i1 } %1, 0
%. = select i1 %2, i64 0, i64 %3
ret i64 %.
}
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