[AMDGPU] Fixed incorrect uniform branch condition
Summary:
I had a case where multiple nested uniform ifs resulted in code that did
v_cmp comparisons, combining the results with s_and_b64, s_or_b64 and
s_xor_b64 and using the resulting mask in s_cbranch_vccnz, without first
ensuring that bits for inactive lanes were clear.
There was already code for inserting an "s_and_b64 vcc, exec, vcc" to
clear bits for inactive lanes in the case that the branch is instruction
selected as s_cbranch_scc1 and is then changed to s_cbranch_vccnz in
SIFixSGPRCopies. I have added the same code into SILowerControlFlow for
the case that the branch is instruction selected as s_cbranch_vccnz.
This de-optimizes the code in some cases where the s_and is not needed,
because vcc is the result of a v_cmp, or multiple v_cmp instructions
combined by s_and/s_or. We should add a pass to re-optimize those cases.
Reviewers: arsenm, kzhuravl
Subscribers: wdng, yaxunl, t-tye, llvm-commits, dstuttard, timcorringham, nhaehnle
Differential Revision: https://reviews.llvm.org/D41292
llvm-svn: 322119
diff --git a/llvm/test/CodeGen/AMDGPU/skip-if-dead.ll b/llvm/test/CodeGen/AMDGPU/skip-if-dead.ll
index 9ae36b0..54fa93a 100644
--- a/llvm/test/CodeGen/AMDGPU/skip-if-dead.ll
+++ b/llvm/test/CodeGen/AMDGPU/skip-if-dead.ll
@@ -267,7 +267,7 @@
; CHECK: [[PHIBB]]:
; CHECK: v_cmp_eq_f32_e32 vcc, 0, [[PHIREG]]
-; CHECK-NEXT: s_cbranch_vccz [[ENDBB:BB[0-9]+_[0-9]+]]
+; CHECK: s_cbranch_vccz [[ENDBB:BB[0-9]+_[0-9]+]]
; CHECK: ; %bb10
; CHECK: v_mov_b32_e32 v{{[0-9]+}}, 9
@@ -302,14 +302,14 @@
; CHECK-LABEL: {{^}}no_skip_no_successors:
; CHECK: v_cmp_nge_f32
-; CHECK-NEXT: s_cbranch_vccz [[SKIPKILL:BB[0-9]+_[0-9]+]]
+; CHECK: s_cbranch_vccz [[SKIPKILL:BB[0-9]+_[0-9]+]]
; CHECK: ; %bb6
; CHECK: s_mov_b64 exec, 0
; CHECK: [[SKIPKILL]]:
; CHECK: v_cmp_nge_f32_e32 vcc
-; CHECK-NEXT: %bb.3: ; %bb5
+; CHECK: %bb.3: ; %bb5
; CHECK-NEXT: .Lfunc_end{{[0-9]+}}
define amdgpu_ps void @no_skip_no_successors(float inreg %arg, float inreg %arg1) #0 {
bb: