[PowerPC] intrinsic llvm.eh.sjlj.setjmp should not have flag isBarrier.

[shchenz]

Summary

This is an issue found when testing PowerPC with verify-machineinstrs.

llc -mtriple=powerpc64-unknown-linux-gnu < llvm/llvm/test/CodeGen/PowerPC/sj-ctr-loop.ll -verify-machineinstrs

Bad machine code: MBB exits via unconditional fall-through but ends with a barrier instruction! ***

        function: main
        basic block: %bb.2 for.body.lr.ph (0x100275437e8)

Content in block BB.2:

BB#2: derived from LLVM BB %for.end
Predecessors according to CFG: BB#1
%vreg2<def> = ADDIStocHA %X2, <ga:@env_sigill>; G8RC_and_G8RC_NOX0:%vreg2
%vreg3<def> = LDtocL <ga:@env_sigill>, %vreg2<kill>; mem:LD8[GOT] G8RC:%vreg3 G8RC_and_G8RC_NOX0:%vreg2
%vreg4<def> = EH_SjLj_SetJmp64 %vreg3<kill>, %CTR8<imp-def,dead>; GPRC:%vreg4 G8RC:%vreg3

A barrier instruction means control flow can not fall through like llvm.eh.sjlj.longjmp and unconditional jumps. But setjmp should fall through. intrinsic llvm.eh.sjlj.setjmp should not have flag isBarrier.

The original case fails at another place after resolving setjmp barrier issue. So I create a new case. And I only focus on PowerPC target, there are some other platforms like ARM, X86 also have same issue.

[nemanjai]

Since we have discovered this in the PPC back end but the issue also exists in ARM and X86, it'd be nice to notify @t.p.northover (already a reviewer) and @craig.topper about this potentially needing to change in their back ends as well.

In any case, other than the minor comments, the PPC portion LGTM.

llvm/lib/Target/PowerPC/PPCInstr64Bit.td

349 ↗

(On Diff #177449)

Please add a comment along the lines of:
While longjmp is a control-flow barrier (fallthrough isn't allowed), setjmp is not.

In both places where we define these (32 and 64 bit).

llvm/test/CodeGen/PowerPC/sjlj.ll

163 ↗

(On Diff #177449)

Put the comment on a separate line. I think this will make FileCheck actually look for all of that text which will clearly always make this test trivially succeed. Also, please correct the typo buildin -> builtin.

[shchenz]

Update according to Nemanjai's comments

llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td

 // Similarly to mfocrf, the mask for mfcrf must be prepared in a way that
 // is dependent on the cr fields being copied.
 def MFCR8 : XFXForm_3<31, 19, (outs g8rc:$rT), (ins),
                      "mfcr $rT", IIC_SprMFCR>,
                      PPC970_MicroCode, PPC970_Unit_CRU;
 } // hasExtraSrcRegAllocReq = 1
 } // hasSideEffects = 0
 
-let hasSideEffects = 1, isBarrier = 1, usesCustomInserter = 1 in {
+// While longjmp is a control-flow barrier (fallthrough isn't allowed), setjmp
+// is not.
+let hasSideEffects = 1, usesCustomInserter = 1 in {
   let Defs = [CTR8] in
   def EH_SjLj_SetJmp64  : Pseudo<(outs gprc:$dst), (ins memr:$buf),
                             "#EH_SJLJ_SETJMP64",
                             [(set i32:$dst, (PPCeh_sjlj_setjmp addr:$buf))]>,
                           Requires<[In64BitMode]>;
+}
+
+let hasSideEffects = 1, isBarrier = 1, usesCustomInserter = 1 in {
   let isTerminator = 1 in
   def EH_SjLj_LongJmp64 : Pseudo<(outs), (ins memr:$buf),
                             "#EH_SJLJ_LONGJMP64",
                             [(PPCeh_sjlj_longjmp addr:$buf)]>,
                           Requires<[In64BitMode]>;
 }
 
 def MFSPR8 : XFXForm_1<31, 339, (outs g8rc:$RT), (ins i32imm:$SPR),

llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td

 let isBranch = 1, isTerminator = 1, hasCtrlDep = 1, PPC970_Unit = 7,
     isBarrier = 1, isCall = 1, isReturn = 1, Uses = [RM] in
 def TAILBA   : IForm<18, 0, 0, (outs), (ins abscalltarget:$dst),
                   "ba $dst", IIC_BrB,
                   []>;
 
 }
 
-let hasSideEffects = 1, isBarrier = 1, usesCustomInserter = 1 in {
+// While longjmp is a control-flow barrier (fallthrough isn't allowed), setjmp
+// is not.
+let hasSideEffects = 1, usesCustomInserter = 1 in {
   let Defs = [CTR] in
   def EH_SjLj_SetJmp32  : Pseudo<(outs gprc:$dst), (ins memr:$buf),
                             "#EH_SJLJ_SETJMP32",
                             [(set i32:$dst, (PPCeh_sjlj_setjmp addr:$buf))]>,
                           Requires<[In32BitMode]>;
+}
+
+let hasSideEffects = 1, isBarrier = 1, usesCustomInserter = 1 in {
   let isTerminator = 1 in
   def EH_SjLj_LongJmp32 : Pseudo<(outs), (ins memr:$buf),
                             "#EH_SJLJ_LONGJMP32",
                             [(PPCeh_sjlj_longjmp addr:$buf)]>,
                           Requires<[In32BitMode]>;
 }
 
 // This pseudo is never removed from the function, as it serves as

llvm/trunk/test/CodeGen/PowerPC/sjlj.ll

-; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 | FileCheck %s
-; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=a2 | FileCheck -check-prefix=CHECK-NOAV %s
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=a2 -verify-machineinstrs | FileCheck -check-prefix=CHECK-NOAV %s
 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-f128:128:128-v128:128:128-n32:64"
 target triple = "powerpc64-unknown-linux-gnu"
 
 %struct.__jmp_buf_tag = type { [64 x i64], i32, %struct.__sigset_t, [8 x i8] }
 %struct.__sigset_t = type { [16 x i64] }
 
 @env_sigill = internal global [1 x %struct.__jmp_buf_tag] zeroinitializer, align 16
+@cond = external global i8, align 1
 
 define void @foo() #0 {
 entry:
   call void @llvm.eh.sjlj.longjmp(i8* bitcast ([1 x %struct.__jmp_buf_tag]* @env_sigill to i8*))
   unreachable
 
 ; CHECK: @foo
 ; CHECK: addis [[REG:[0-9]+]], 2, env_sigill@toc@ha

 ; CHECK-DAG: std 1, 16([[REGB]])
 ; CHECK-DAG: std 2, 24([[REGB]])
 ; CHECK-DAG: std 30, 32([[REGB]])
 ; CHECK: bcl 20, 31,
 
 ; CHECK: blr
 }
 
+define void @test_sjlj_setjmp() #0 {
+entry:
+  %0 = load i8, i8* @cond, align 1
+  %tobool = trunc i8 %0 to i1
+  br i1 %tobool, label %return, label %end
+
+end:
+  %1 = call i32 @llvm.eh.sjlj.setjmp(i8* bitcast ([1 x %struct.__jmp_buf_tag]* @env_sigill to i8*))
+  br label %return
+
+return:
+  ret void
+
+; CHECK-LABEL: test_sjlj_setjmp:
+; intrinsic llvm.eh.sjlj.setjmp does not call builtin function _setjmp.
+; CHECK-NOT: bl _setjmp
+}
+
 declare void @bar(i8*) #3
 
 declare i8* @llvm.frameaddress(i32) #2
 
 declare i8* @llvm.stacksave() #3
 
 declare i32 @llvm.eh.sjlj.setjmp(i8*) #3
 
 attributes #0 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #1 = { noreturn nounwind }
 attributes #2 = { nounwind readnone }
 attributes #3 = { nounwind }