AMDGPU: Add implicit def of SCC to kill and indirect pseudos

Summary:
Kill instructions sometimes do use SCC in unusual circumstances, when
v_cmpx cannot be used due to the operands that are involved.

Additionally, even if SCC was never defined by the expansion, kill pseudos
could previously occur between an s_cmp and an s_cbranch_scc, which breaks
the SCC liveness tracking when the pseudo is expanded to split the basic
block. While it would be possible to explicitly mark the SCC as live-in for
the successor basic block, it's simpler to just mark the pseudo as using SCC,
so that such a sequence is never emitted by instruction selection in the
first place.

A similar issue affects indirect source/dest pseudos in principle, although
I haven't been able to come up with a test case where it actually matters
(this affects instruction selection, so a MIR test can't be used).

Fixes: dEQP-GLES3.functional.shaders.discard.dynamic_loop_always
Change-Id: Ica8d82ecff1a763b892a1112cf1b06c948863a4f

Reviewers: arsenm, rampitec

Subscribers: kzhuravl, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D47761

llvm-svn: 335223

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIInstructions.td b/llvm/lib/Target/AMDGPU/SIInstructions.td
index a3b4ea008fe..87a891bb361 100644
--- a/llvm/lib/Target/AMDGPU/SIInstructions.td
+++ b/llvm/lib/Target/AMDGPU/SIInstructions.td
@@ -292,14 +292,21 @@ def SI_ELSE_BREAK : CFPseudoInstSI <
   let isReMaterializable = 1;
 }
 
-let Uses = [EXEC], Defs = [EXEC,VCC] in {
+let Uses = [EXEC] in {
 
 multiclass PseudoInstKill <dag ins> {
+  // Even though this pseudo can usually be expanded without an SCC def, we
+  // conservatively assume that it has an SCC def, both because it is sometimes
+  // required in degenerate cases (when V_CMPX cannot be used due to constant
+  // bus limitations) and because it allows us to avoid having to track SCC
+  // liveness across basic blocks.
+  let Defs = [EXEC,VCC,SCC] in
   def _PSEUDO : PseudoInstSI <(outs), ins> {
     let isConvergent = 1;
     let usesCustomInserter = 1;
   }
 
+  let Defs = [EXEC,VCC,SCC] in
   def _TERMINATOR : SPseudoInstSI <(outs), ins> {
     let isTerminator = 1;
   }
@@ -308,6 +315,7 @@ multiclass PseudoInstKill <dag ins> {
 defm SI_KILL_I1 : PseudoInstKill <(ins SSrc_b64:$src, i1imm:$killvalue)>;
 defm SI_KILL_F32_COND_IMM : PseudoInstKill <(ins VSrc_b32:$src0, i32imm:$src1, i32imm:$cond)>;
 
+let Defs = [EXEC,VCC] in
 def SI_ILLEGAL_COPY : SPseudoInstSI <
   (outs unknown:$dst), (ins unknown:$src),
   [], " ; illegal copy $src to $dst">;
@@ -445,7 +453,7 @@ def ADJCALLSTACKDOWN : SPseudoInstSI<
   let usesCustomInserter = 1;
 }
 
-let Defs = [M0, EXEC],
+let Defs = [M0, EXEC, SCC],
   UseNamedOperandTable = 1 in {
 
 class SI_INDIRECT_SRC<RegisterClass rc> : VPseudoInstSI <