[llvm] r373293 - AMDGPU/GlobalISel: Avoid creating shift of 0 in arg lowering

[Matt Arsenault via llvm-commits]

Author: arsenm
Date: Mon Sep 30 18:44:46 2019
New Revision: 373293

URL: http://llvm.org/viewvc/llvm-project?rev=373293&view=rev
Log:
AMDGPU/GlobalISel: Avoid creating shift of 0 in arg lowering

This is sort of papering over the fact that we don't run a combiner
anywhere, but avoiding creating 2 instructions in the first place is
easy.

Modified:
    llvm/trunk/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
    llvm/trunk/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.workitem.id.ll

Modified: llvm/trunk/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp?rev=373293&r1=373292&r2=373293&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp (original)
+++ llvm/trunk/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp Mon Sep 30 18:44:46 2019
@@ -1717,9 +1717,14 @@ bool AMDGPULegalizerInfo::loadInputValue
     const unsigned Mask = Arg->getMask();
     const unsigned Shift = countTrailingZeros<unsigned>(Mask);
 
-    auto ShiftAmt = B.buildConstant(S32, Shift);
-    auto LShr = B.buildLShr(S32, LiveIn, ShiftAmt);
-    B.buildAnd(DstReg, LShr, B.buildConstant(S32, Mask >> Shift));
+    Register AndMaskSrc = LiveIn;
+
+    if (Shift != 0) {
+      auto ShiftAmt = B.buildConstant(S32, Shift);
+      AndMaskSrc = B.buildLShr(S32, LiveIn, ShiftAmt).getReg(0);
+    }
+
+    B.buildAnd(DstReg, AndMaskSrc, B.buildConstant(S32, Mask >> Shift));
   } else
     B.buildCopy(DstReg, LiveIn);
 

Modified: llvm/trunk/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.workitem.id.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.workitem.id.ll?rev=373293&r1=373292&r2=373293&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.workitem.id.ll (original)
+++ llvm/trunk/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.workitem.id.ll Mon Sep 30 18:44:46 2019
@@ -89,7 +89,7 @@ bb2:
 }
 
 ; ALL-LABEL: {{^}}test_workitem_id_x_func:
-; ALL: v_lshrrev_b32_e32 v2, 0, v2
+; ALL: s_waitcnt
 ; ALL-NEXT: v_and_b32_e32 v2, 0x3ff, v2
 define void @test_workitem_id_x_func(i32 addrspace(1)* %out) #1 {
   %id = call i32 @llvm.amdgcn.workitem.id.x()