https://bugs.llvm.org/show_bug.cgi?id=32964
Bug ID: 32964
Summary: load from @i hoisted before store to @i by
-speculative-execution
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: mikael.hol...@ericsson.com
CC: llvm-bugs@lists.llvm.org
Created attachment 18415
--> https://bugs.llvm.org/attachment.cgi?id=18415&action=edit
reproducer
opt -S -speculative-execution -o - spec.ll
In the input we have:
entry:
%0 = load i8, i8* @i
%tobool = icmp eq i8 %0, 0
br i1 %tobool, label %if.end, label %if.then
if.then: ; preds = %entry
store i8 0, i8* @i
%.pre = load i8, i8* @i
br label %if.end
and in the output we get:
entry:
%0 = load i8, i8* @i
%tobool = icmp eq i8 %0, 0
%.pre = load i8, i8* @i
br i1 %tobool, label %if.end, label %if.then
if.then: ; preds = %entry
store i8 0, i8* @i
br label %if.end
so
%.pre = load i8, i8* @i
has been moved before
store i8 0, i8* @i
and we'll load the old (wrong) value.
This started going wrong after commit
SpeculativeExecution: Stop using whitelist for costs
but I suppose that is because costs in general went down
with that patch so it triggers in more cases.
This seems very broken to me and I see these errors a lot in our out-of-tree
backend.
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