Machine sink could potentially sink instructions into a block where the physical

registers it defines then interfere with an existing preg live range.

For instance, if we had something like these machine instructions:

BB#0
  ... = imul ... EFLAGS<imp-def,dead>
  test ..., EFLAGS<imp-def>
  jcc BB#2 EFLAGS<imp-use>

BB#1
  ... ; fallthrough to BB#2

BB#2
  ... ; No code that defines EFLAGS
  jcc ... EFLAGS<imp-use>

Machine sink will come along, see that imul implicitly defines EFLAGS, but
because it's "dead", it assumes that it can move imul into BB#2. But when it
does, imul's "dead" imp-def of EFLAGS is raised from the dead (a zombie) and
messes up the condition code for the jump (and pretty much anything else which
relies upon it being correct).

The solution is to know which pregs are live going into a basic block. However,
that information isn't calculated at this point. Nor does the LiveVariables pass
take into account non-allocatable physical registers. In lieu of this, we do a
*very* conservative pass through the basic block to determine if a preg is live
coming out of it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105387 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 23 insertions, 16 deletions

diff --git a/test/CodeGen/X86/sink-hoist.ll b/test/CodeGen/X86/sink-hoist.ll
index 031c01e..acba528 100644
--- a/test/CodeGen/X86/sink-hoist.ll
+++ b/test/CodeGen/X86/sink-hoist.ll
@@ -44,26 +44,33 @@ return:
 
 ; Sink instructions with dead EFLAGS defs.
 
-; CHECK: zzz:
-; CHECK:      je
-; CHECK-NEXT: orb
-
-define zeroext i8 @zzz(i8 zeroext %a, i8 zeroext %b) nounwind readnone {
-entry:
-  %tmp = zext i8 %a to i32                        ; <i32> [#uses=1]
-  %tmp2 = icmp eq i8 %a, 0                    ; <i1> [#uses=1]
-  %tmp3 = or i8 %b, -128                          ; <i8> [#uses=1]
-  %tmp4 = and i8 %b, 127                          ; <i8> [#uses=1]
-  %b_addr.0 = select i1 %tmp2, i8 %tmp4, i8 %tmp3 ; <i8> [#uses=1]
-  ret i8 %b_addr.0
-}
+; FIXME: Unfail the zzz test if we can correctly mark pregs with the kill flag.
+; 
+; See <rdar://problem/8030636>. This test isn't valid after we made machine
+; sinking more conservative about sinking instructions that define a preg into a
+; block when we don't know if the preg is killed within the current block.
+
+
+; FIXMEHECK: zzz:
+; FIXMEHECK:      je
+; FIXMEHECK-NEXT: orb
+
+; define zeroext i8 @zzz(i8 zeroext %a, i8 zeroext %b) nounwind readnone {
+; entry:
+;   %tmp = zext i8 %a to i32                        ; <i32> [#uses=1]
+;   %tmp2 = icmp eq i8 %a, 0                    ; <i1> [#uses=1]
+;   %tmp3 = or i8 %b, -128                          ; <i8> [#uses=1]
+;   %tmp4 = and i8 %b, 127                          ; <i8> [#uses=1]
+;   %b_addr.0 = select i1 %tmp2, i8 %tmp4, i8 %tmp3 ; <i8> [#uses=1]
+;   ret i8 %b_addr.0
+; }
 
 ; Codegen should hoist and CSE these constants.
 
 ; CHECK: vv:
-; CHECK: LCPI3_0(%rip), %xmm0
-; CHECK: LCPI3_1(%rip), %xmm1
-; CHECK: LCPI3_2(%rip), %xmm2
+; CHECK: LCPI2_0(%rip), %xmm0
+; CHECK: LCPI2_1(%rip), %xmm1
+; CHECK: LCPI2_2(%rip), %xmm2
 ; CHECK: align
 ; CHECK-NOT: LCPI
 ; CHECK: ret