bpf: Tighten subregister definition check

The current subregister definition check stops after the MOV_32_64
instruction.

This means we are thinking all the following instruction sequences
are safe to be eliminated:

  MOV_32_64 rB, wA
  SLL_ri    rB, rB, 32
  SRL_ri    rB, rB, 32

However, this is *not* true. The source subregister wA of MOV_32_64 could
come from a implicit truncation of 64-bit register in which case the high
bits of the 64-bit register is not zeroed, therefore we can't eliminate
above sequence.

For example, for i32_val, we shouldn't do the elimination:

  long long bar ();

  int foo (int b, int c)
  {
    unsigned int i32_val = (unsigned int) bar();

    if (i32_val < 10)
      return b;
    else
      return c;
  }

Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 327365

1 files changed, 32 insertions, 1 deletions

diff --git a/llvm/test/CodeGen/BPF/32-bit-subreg-peephole.ll b/llvm/test/CodeGen/BPF/32-bit-subreg-peephole.ll
index 826ab2b8362..6b3edaf9cf9 100644
--- a/llvm/test/CodeGen/BPF/32-bit-subreg-peephole.ll
+++ b/llvm/test/CodeGen/BPF/32-bit-subreg-peephole.ll
@@ -14,7 +14,20 @@
 ;     return c;
 ;   else
 ;     return d;
-;}
+; }
+;
+; long long bar ();
+;
+; int foo (int b, int c)
+; {
+;   unsigned int i32_val = (unsigned int) bar();
+;
+;   if (i32_val < 10)
+;     return b;
+;   else
+;     return c;
+; }
+
 ; Function Attrs: norecurse nounwind readnone
 define dso_local i64 @select_u(i32 %a, i32 %b, i64 %c, i64 %d) local_unnamed_addr #0 {
 ; CHECK-LABEL: select_u:
@@ -38,3 +51,21 @@ entry:
 ; CHECK: if r{{[0-9]+}} s{{<|>}} r{{[0-9]+}} goto
   ret i64 %c.d
 }
+
+; Function Attrs: nounwind
+define dso_local i32 @foo(i32 %b, i32 %c) local_unnamed_addr #0 {
+; CHECK-LABEL: foo:
+entry:
+  %call = tail call i64 bitcast (i64 (...)* @bar to i64 ()*)() #2
+  %conv = trunc i64 %call to i32
+  %cmp = icmp ult i32 %conv, 10
+; The shifts can't be optimized out because %call comes from function call
+; returning i64 so the high bits might be valid.
+; CHECK: r{{[0-9]+}} <<= 32
+; CHECK-NEXT: r{{[0-9]+}} >>= 32
+  %b.c = select i1 %cmp, i32 %b, i32 %c
+; CHECK: if r{{[0-9]+}} {{<|>}} {{[0-9]+}} goto
+  ret i32 %b.c
+}
+
+declare dso_local i64 @bar(...) local_unnamed_addr #1