http://llvm.org/bugs/show_bug.cgi?id=12513
Bug #: 12513
Summary: Loop unrolling breaks with indirect branches
Product: libraries
Version: trunk
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: Loop Optimizer
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
Simple test case:
; ModuleID = 'blah.ll'
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-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
declare void @subtract() nounwind uwtable
define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable {
entry:
%vals19 = alloca [5 x i32], align 16
%x20 = alloca i32, align 4
store i32 135, i32* %x20, align 4
br label %for.body
for.body: ; preds = %call2_termjoin,
%call3_termjoin
%indvars.iv = phi i64 [ 0, %entry ], [ %joinphi15.in.in, %call2_termjoin ]
%a6 = call coldcc i8* @funca(i8* blockaddress(@main, %for.body_code), i8*
blockaddress(@main, %for.body_codeprime)) nounwind
indirectbr i8* %a6, [label %for.body_code, label %for.body_codeprime]
for.body_code: ; preds = %for.body
call void @subtract()
br label %call2_termjoin
call2_termjoin: ; preds =
%for.body_codeprime, %for.body_code
%joinphi15.in.in = add i64 %indvars.iv, 1
%exitcond = icmp eq i64 %joinphi15.in.in, 5
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %call2_termjoin
ret i32 0
for.body_codeprime: ; preds = %for.body
call void @subtract_v2(i64 %indvars.iv)
br label %call2_termjoin
}
declare coldcc i8* @funca(i8*, i8*) readonly
declare void @subtract_v2(i64) nounwind uwtable
Compile with -loop-unroll and -simplifycfg. Result:
; ModuleID = 'blah.ll'
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-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
declare void @subtract() nounwind uwtable
define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable {
entry:
%vals19 = alloca [5 x i32], align 16
%x20 = alloca i32, align 4
store i32 135, i32* %x20, align 4
%a6 = call coldcc i8* @funca(i8* blockaddress(@main, %for.body_code), i8*
blockaddress(@main, %for.body_codeprime)) nounwind
indirectbr i8* %a6, [label %for.body_code, label %for.body_codeprime]
for.body_code: ; preds = %entry
call void @subtract()
unreachable
for.body_codeprime: ; preds = %entry
call void @subtract_v2(i64 0)
unreachable
}
declare coldcc i8* @funca(i8*, i8*) readonly
declare void @subtract_v2(i64) nounwind uwtable
Loop unrolling decides to unroll the loop, which clones the indirectbr, giving
each target of indirectbr different successors. Simplifycfgs notes that the
targets can never be reached by address, and helpfully deletes all successors
of indirectbr. As a result, the indirectbr has no possible successors, so it
marks it unreachable and proceeds to completely break code.
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