http://llvm.org/bugs/show_bug.cgi?id=2993
Summary: instcombine causes miscompilation with rems -1
Product: new-bugs
Version: unspecified
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: new bugs
AssignedTo: [EMAIL PROTECTED]
ReportedBy: [EMAIL PROTECTED]
CC: [email protected]
Running "opt -instcombine" on the following testcase:
define i1 @main_bb_bb_2E_ce(i32 %i.0.reg2mem.0) {
newFuncRoot:
br label %bb.ce
bb2.exitStub: ; preds = %bb.ce
ret i1 true
codeRepl1.exitStub: ; preds = %bb.ce
ret i1 false
bb.ce: ; preds = %newFuncRoot
%0 = srem i32 %i.0.reg2mem.0, -1 ; <i32> [#uses=1]
%1 = icmp eq i32 %0, 0 ; <i1> [#uses=1]
br i1 %1, label %bb2.exitStub, label %codeRepl1.exitStub
}
turns it into:
define i1 @main_bb_bb_2E_ce(i32 %i.0.reg2mem.0) {
newFuncRoot:
br label %bb.ce
bb2.exitStub: ; preds = %bb.ce
ret i1 true
codeRepl1.exitStub: ; preds = %bb.ce
ret i1 false
bb.ce: ; preds = %newFuncRoot
%0 = icmp eq i32 %i.0.reg2mem.0, 0 ; <i1> [#uses=1]
br i1 %0, label %bb2.exitStub, label %codeRepl1.exitStub
}
This transformation is incorrect. Instruction Combine should not be turning
%0 = srem i32 %i.0.reg2mem.0, -1 ; <i32> [#uses=1]
%1 = icmp eq i32 %0, 0 ; <i1> [#uses=1]
into
%0 = icmp eq i32 %i.0.reg2mem.0, 0 ; <i1> [#uses=1]
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