Index: lib/Target/AMDGPU/SIInstrInfo.cpp
===================================================================
--- lib/Target/AMDGPU/SIInstrInfo.cpp
+++ lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -2131,9 +2131,8 @@
   const MachineFunction *MF = MO->getParent()->getParent()->getParent();
   const MachineRegisterInfo &MRI = MF->getRegInfo();
   auto Def = MRI.getUniqueVRegDef(MO->getReg());
-  if (Def && (Def->getOpcode() == AMDGPU::S_MOV_B32 ||
-              Def->getOpcode() == AMDGPU::V_MOV_B32_e32) &&
-     Def->getOperand(1).isImm())
+  if (Def && Def->getOpcode() == AMDGPU::V_MOV_B32_e32 &&
+      Def->getOperand(1).isImm())
     return Def->getOperand(1).getImm();
   return AMDGPU::NoRegister;
 }
@@ -2175,7 +2174,9 @@
   const MachineOperand *Clamp = getNamedOperand(MI, AMDGPU::OpName::clamp);
   const MachineOperand *Omod = getNamedOperand(MI, AMDGPU::OpName::omod);
 
-  if (!Src0Mods && !Src1Mods && !Clamp && !Omod) {
+  if (!Src0Mods && !Src1Mods && !Clamp && !Omod &&
+      // If we have an SGPR input, we will violate the constant bus restriction.
+      !RI.isSGPRReg(MBB->getParent()->getRegInfo(), Src0->getReg())) {
     if (auto Imm = getFoldableImm(Src2)) {
       return BuildMI(*MBB, MI, MI.getDebugLoc(),
                      get(IsF16 ? AMDGPU::V_MADAK_F16 : AMDGPU::V_MADAK_F32))
Index: test/CodeGen/AMDGPU/twoaddr-mad.mir
===================================================================
--- test/CodeGen/AMDGPU/twoaddr-mad.mir
+++ test/CodeGen/AMDGPU/twoaddr-mad.mir
@@ -108,3 +108,25 @@
     %1 = V_MOV_B32_e32 1078523331, implicit %exec
     %2 = V_MAC_F16_e32 killed %0.sub0, %0.sub1, %1, implicit %exec
 ...
+
+# Make sure constant bus restriction isn't violated if src0 is an SGPR.
+
+# GCN-LABEL: name: test_madak_sgpr_src0_f32
+# GCN: %1 = V_MOV_B32_e32 1078523331, implicit %exec
+# GCN: %2 = V_MAD_F32 0, killed %0, 0, %1, 0, %3, 0, 0, implicit %exec
+
+---
+name:            test_madak_sgpr_src0_f32
+registers:
+  - { id: 0, class: sreg_32_xm0 }
+  - { id: 1, class: vgpr_32}
+  - { id: 2, class: vgpr_32 }
+  - { id: 3, class: vgpr_32 }
+body:             |
+  bb.0:
+
+    %0 = IMPLICIT_DEF
+    %1 = V_MOV_B32_e32 1078523331, implicit %exec
+    %2 = V_MAC_F32_e32 killed %0, %1, %3, implicit %exec
+
+...