[AMDGPU] Spill CSR VGPR which is reserved for SGPR spills

Update logic for reserving VGPR for SGPR spills. A CSR VGPR being reserved for SGPR spills could be clobbered if there were no free lower VGPR's available. Create a stack object so that it will be spilled in the prologue. Also adds more tests. Differential Revision: https://reviews.llvm.org/D83730
llvm · Jul 28, 2020 · adeeac9 · adeeac9
1 parent 834133c
commit adeeac9
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diff --git a/llvm/lib/Target/AMDGPU/SILowerSGPRSpills.cpp b/llvm/lib/Target/AMDGPU/SILowerSGPRSpills.cpp
@@ -233,10 +233,18 @@ bool SILowerSGPRSpills::spillCalleeSavedRegs(MachineFunction &MF) {
 // Find lowest available VGPR and use it as VGPR reserved for SGPR spills.
 static bool lowerShiftReservedVGPR(MachineFunction &MF,
                                    const GCNSubtarget &ST) {
+  SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
+  const Register PreReservedVGPR = FuncInfo->VGPRReservedForSGPRSpill;
+  // Early out if pre-reservation of a VGPR for SGPR spilling is disabled.
+  if (!PreReservedVGPR)
+    return false;
+
+  // If there are no free lower VGPRs available, default to using the
+  // pre-reserved register instead.
+  Register LowestAvailableVGPR = PreReservedVGPR;
+
   MachineRegisterInfo &MRI = MF.getRegInfo();
   MachineFrameInfo &FrameInfo = MF.getFrameInfo();
-  SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
-  Register LowestAvailableVGPR, ReservedVGPR;
   ArrayRef<MCPhysReg> AllVGPR32s = ST.getRegisterInfo()->getAllVGPR32(MF);
   for (MCPhysReg Reg : AllVGPR32s) {
     if (MRI.isAllocatable(Reg) && !MRI.isPhysRegUsed(Reg)) {
@@ -245,26 +253,29 @@ static bool lowerShiftReservedVGPR(MachineFunction &MF,
     }
   }
 
-  if (!LowestAvailableVGPR)
-    return false;
-
-  ReservedVGPR = FuncInfo->VGPRReservedForSGPRSpill;
   const MCPhysReg *CSRegs = MF.getRegInfo().getCalleeSavedRegs();
-  int i = 0;
+  Optional<int> FI;
+  // Check if we are reserving a CSR. Create a stack object for a possible spill
+  // in the function prologue.
+  if (FuncInfo->isCalleeSavedReg(CSRegs, LowestAvailableVGPR))
+    FI = FrameInfo.CreateSpillStackObject(4, Align(4));
+
+  // Find saved info about the pre-reserved register.
+  const auto *ReservedVGPRInfoItr =
+      std::find_if(FuncInfo->getSGPRSpillVGPRs().begin(),
+                   FuncInfo->getSGPRSpillVGPRs().end(),
+                   [PreReservedVGPR](const auto &SpillRegInfo) {
+                     return SpillRegInfo.VGPR == PreReservedVGPR;
+                   });
+
+  assert(ReservedVGPRInfoItr != FuncInfo->getSGPRSpillVGPRs().end());
+  auto Index =
+      std::distance(FuncInfo->getSGPRSpillVGPRs().begin(), ReservedVGPRInfoItr);
+
+  FuncInfo->setSGPRSpillVGPRs(LowestAvailableVGPR, FI, Index);
 
   for (MachineBasicBlock &MBB : MF) {
-    for (auto Reg : FuncInfo->getSGPRSpillVGPRs()) {
-      if (Reg.VGPR == ReservedVGPR) {
-        MBB.removeLiveIn(ReservedVGPR);
-        MBB.addLiveIn(LowestAvailableVGPR);
-        Optional<int> FI;
-        if (FuncInfo->isCalleeSavedReg(CSRegs, LowestAvailableVGPR))
-          FI = FrameInfo.CreateSpillStackObject(4, Align(4));
-
-        FuncInfo->setSGPRSpillVGPRs(LowestAvailableVGPR, FI, i);
-      }
-      ++i;
-    }
+    MBB.addLiveIn(LowestAvailableVGPR);
     MBB.sortUniqueLiveIns();
   }
 

diff --git a/llvm/test/CodeGen/AMDGPU/reserve-vgpr-for-sgpr-spill.ll b/llvm/test/CodeGen/AMDGPU/reserve-vgpr-for-sgpr-spill.ll
@@ -5,17 +5,21 @@ define void @child_function() #0 {
   ret void
 }
 
-; GCN-LABEL: {{^}}parent_func:
-; CHECK: 	v_writelane_b32 v255, s33, 2
-; CHECK: 	v_writelane_b32 v255, s30, 0
-; CHECK: 	v_writelane_b32 v255, s31, 1
-; CHECK:  s_swappc_b64 s[30:31], s[4:5]
-; CHECK: 	v_readlane_b32 s4, v255, 0
-; CHECK:  v_readlane_b32 s5, v255, 1
-; CHECK: 	v_readlane_b32 s33, v255, 2
+; GCN-LABEL: {{^}}reserve_vgpr_with_no_lower_vgpr_available:
+; GCN:  buffer_store_dword v255, off, s[0:3], s32
+; GCN:  v_writelane_b32 v255, s33, 2
+; GCN:  v_writelane_b32 v255, s30, 0
+; GCN:  v_writelane_b32 v255, s31, 1
+; GCN:  s_swappc_b64 s[30:31], s[4:5]
+; GCN:  v_readlane_b32 s4, v255, 0
+; GCN:  v_readlane_b32 s5, v255, 1
+; GCN:  v_readlane_b32 s33, v255, 2
 ; GCN: ; NumVgprs: 256
 
-define void @parent_func() #0 {
+define void @reserve_vgpr_with_no_lower_vgpr_available() #0 {
+  %alloca = alloca i32, align 4, addrspace(5)
+  store volatile i32 0, i32 addrspace(5)* %alloca
+
   call void asm sideeffect "",
   "~{v0},~{v1},~{v2},~{v3},~{v4},~{v5},~{v6},~{v7},~{v8},~{v9}
   ,~{v10},~{v11},~{v12},~{v13},~{v14},~{v15},~{v16},~{v17},~{v18},~{v19}
@@ -47,4 +51,140 @@ define void @parent_func() #0 {
   ret void
 }
 
+; GCN-LABEL: {{^}}reserve_lowest_available_vgpr:
+; GCN:  buffer_store_dword v254, off, s[0:3], s32
+; GCN:  v_writelane_b32 v254, s33, 2
+; GCN:  v_writelane_b32 v254, s30, 0
+; GCN:  v_writelane_b32 v254, s31, 1
+; GCN:  s_swappc_b64 s[30:31], s[4:5]
+; GCN:  v_readlane_b32 s4, v254, 0
+; GCN:  v_readlane_b32 s5, v254, 1
+; GCN:  v_readlane_b32 s33, v254, 2
+
+define void @reserve_lowest_available_vgpr() #0 {
+  %alloca = alloca i32, align 4, addrspace(5)
+  store volatile i32 0, i32 addrspace(5)* %alloca
+
+  call void asm sideeffect "",
+  "~{v0},~{v1},~{v2},~{v3},~{v4},~{v5},~{v6},~{v7},~{v8},~{v9}
+  ,~{v10},~{v11},~{v12},~{v13},~{v14},~{v15},~{v16},~{v17},~{v18},~{v19}
+  ,~{v20},~{v21},~{v22},~{v23},~{v24},~{v25},~{v26},~{v27},~{v28},~{v29}
+  ,~{v30},~{v31},~{v32},~{v33},~{v34},~{v35},~{v36},~{v37},~{v38},~{v39}
+  ,~{v40},~{v41},~{v42},~{v43},~{v44},~{v45},~{v46},~{v47},~{v48},~{v49}
+  ,~{v50},~{v51},~{v52},~{v53},~{v54},~{v55},~{v56},~{v57},~{v58},~{v59}
+  ,~{v60},~{v61},~{v62},~{v63},~{v64},~{v65},~{v66},~{v67},~{v68},~{v69}
+  ,~{v70},~{v71},~{v72},~{v73},~{v74},~{v75},~{v76},~{v77},~{v78},~{v79}
+  ,~{v80},~{v81},~{v82},~{v83},~{v84},~{v85},~{v86},~{v87},~{v88},~{v89}
+  ,~{v90},~{v91},~{v92},~{v93},~{v94},~{v95},~{v96},~{v97},~{v98},~{v99}
+  ,~{v100},~{v101},~{v102},~{v103},~{v104},~{v105},~{v106},~{v107},~{v108},~{v109}
+  ,~{v110},~{v111},~{v112},~{v113},~{v114},~{v115},~{v116},~{v117},~{v118},~{v119}
+  ,~{v120},~{v121},~{v122},~{v123},~{v124},~{v125},~{v126},~{v127},~{v128},~{v129}
+  ,~{v130},~{v131},~{v132},~{v133},~{v134},~{v135},~{v136},~{v137},~{v138},~{v139}
+  ,~{v140},~{v141},~{v142},~{v143},~{v144},~{v145},~{v146},~{v147},~{v148},~{v149}
+  ,~{v150},~{v151},~{v152},~{v153},~{v154},~{v155},~{v156},~{v157},~{v158},~{v159}
+  ,~{v160},~{v161},~{v162},~{v163},~{v164},~{v165},~{v166},~{v167},~{v168},~{v169}
+  ,~{v170},~{v171},~{v172},~{v173},~{v174},~{v175},~{v176},~{v177},~{v178},~{v179}
+  ,~{v180},~{v181},~{v182},~{v183},~{v184},~{v185},~{v186},~{v187},~{v188},~{v189}
+  ,~{v190},~{v191},~{v192},~{v193},~{v194},~{v195},~{v196},~{v197},~{v198},~{v199}
+  ,~{v200},~{v201},~{v202},~{v203},~{v204},~{v205},~{v206},~{v207},~{v208},~{v209}
+  ,~{v210},~{v211},~{v212},~{v213},~{v214},~{v215},~{v216},~{v217},~{v218},~{v219}
+  ,~{v220},~{v221},~{v222},~{v223},~{v224},~{v225},~{v226},~{v227},~{v228},~{v229}
+  ,~{v230},~{v231},~{v232},~{v233},~{v234},~{v235},~{v236},~{v237},~{v238},~{v239}
+  ,~{v240},~{v241},~{v242},~{v243},~{v244},~{v245},~{v246},~{v247},~{v248},~{v249}
+  ,~{v250},~{v251},~{v252},~{v253}" () #0
+  call void @child_function()
+  ret void
+}
+
+; GCN-LABEL: {{^}}reserve_vgpr_with_sgpr_spills:
+; GCN-NOT:  buffer_store_dword v255, off, s[0:3], s32
+; GCN: ; def s4
+; GCN: v_writelane_b32 v254, s4, 2
+; GCN: v_readlane_b32 s4, v254, 2
+; GCN: ; use s4
+
+define void @reserve_vgpr_with_sgpr_spills() #0 {
+  %alloca = alloca i32, align 4, addrspace(5)
+  store volatile i32 0, i32 addrspace(5)* %alloca
+
+  call void asm sideeffect "",
+  "~{v0},~{v1},~{v2},~{v3},~{v4},~{v5},~{v6},~{v7},~{v8},~{v9}
+  ,~{v10},~{v11},~{v12},~{v13},~{v14},~{v15},~{v16},~{v17},~{v18},~{v19}
+  ,~{v20},~{v21},~{v22},~{v23},~{v24},~{v25},~{v26},~{v27},~{v28},~{v29}
+  ,~{v30},~{v31},~{v32},~{v33},~{v34},~{v35},~{v36},~{v37},~{v38},~{v39}
+  ,~{v40},~{v41},~{v42},~{v43},~{v44},~{v45},~{v46},~{v47},~{v48},~{v49}
+  ,~{v50},~{v51},~{v52},~{v53},~{v54},~{v55},~{v56},~{v57},~{v58},~{v59}
+  ,~{v60},~{v61},~{v62},~{v63},~{v64},~{v65},~{v66},~{v67},~{v68},~{v69}
+  ,~{v70},~{v71},~{v72},~{v73},~{v74},~{v75},~{v76},~{v77},~{v78},~{v79}
+  ,~{v80},~{v81},~{v82},~{v83},~{v84},~{v85},~{v86},~{v87},~{v88},~{v89}
+  ,~{v90},~{v91},~{v92},~{v93},~{v94},~{v95},~{v96},~{v97},~{v98},~{v99}
+  ,~{v100},~{v101},~{v102},~{v103},~{v104},~{v105},~{v106},~{v107},~{v108},~{v109}
+  ,~{v110},~{v111},~{v112},~{v113},~{v114},~{v115},~{v116},~{v117},~{v118},~{v119}
+  ,~{v120},~{v121},~{v122},~{v123},~{v124},~{v125},~{v126},~{v127},~{v128},~{v129}
+  ,~{v130},~{v131},~{v132},~{v133},~{v134},~{v135},~{v136},~{v137},~{v138},~{v139}
+  ,~{v140},~{v141},~{v142},~{v143},~{v144},~{v145},~{v146},~{v147},~{v148},~{v149}
+  ,~{v150},~{v151},~{v152},~{v153},~{v154},~{v155},~{v156},~{v157},~{v158},~{v159}
+  ,~{v160},~{v161},~{v162},~{v163},~{v164},~{v165},~{v166},~{v167},~{v168},~{v169}
+  ,~{v170},~{v171},~{v172},~{v173},~{v174},~{v175},~{v176},~{v177},~{v178},~{v179}
+  ,~{v180},~{v181},~{v182},~{v183},~{v184},~{v185},~{v186},~{v187},~{v188},~{v189}
+  ,~{v190},~{v191},~{v192},~{v193},~{v194},~{v195},~{v196},~{v197},~{v198},~{v199}
+  ,~{v200},~{v201},~{v202},~{v203},~{v204},~{v205},~{v206},~{v207},~{v208},~{v209}
+  ,~{v210},~{v211},~{v212},~{v213},~{v214},~{v215},~{v216},~{v217},~{v218},~{v219}
+  ,~{v220},~{v221},~{v222},~{v223},~{v224},~{v225},~{v226},~{v227},~{v228},~{v229}
+  ,~{v230},~{v231},~{v232},~{v233},~{v234},~{v235},~{v236},~{v237},~{v238},~{v239}
+  ,~{v240},~{v241},~{v242},~{v243},~{v244},~{v245},~{v246},~{v247},~{v248},~{v249}
+  ,~{v250},~{v251},~{v252},~{v253}" () #0
+
+  %sgpr = call i32 asm sideeffect "; def $0", "=s" () #0
+  %cmp = icmp eq i32 undef, 0
+  br i1 %cmp, label %bb0, label %ret
+
+bb0:
+  call void asm sideeffect "; use $0", "s"(i32 %sgpr) #0
+  br label %ret
+
+ret:
+  ret void
+}
+
+; GCN-LABEL: {{^}}reserve_vgpr_with_tail_call
+; GCN-NOT:  buffer_store_dword v255, off, s[0:3], s32
+; GCN-NOT:  v_writelane
+; GCN:  s_setpc_b64 s[4:5]
+
+define void @reserve_vgpr_with_tail_call() #0 {
+  %alloca = alloca i32, align 4, addrspace(5)
+  store volatile i32 0, i32 addrspace(5)* %alloca
+
+  call void asm sideeffect "",
+  "~{v0},~{v1},~{v2},~{v3},~{v4},~{v5},~{v6},~{v7},~{v8},~{v9}
+  ,~{v10},~{v11},~{v12},~{v13},~{v14},~{v15},~{v16},~{v17},~{v18},~{v19}
+  ,~{v20},~{v21},~{v22},~{v23},~{v24},~{v25},~{v26},~{v27},~{v28},~{v29}
+  ,~{v30},~{v31},~{v32},~{v33},~{v34},~{v35},~{v36},~{v37},~{v38},~{v39}
+  ,~{v40},~{v41},~{v42},~{v43},~{v44},~{v45},~{v46},~{v47},~{v48},~{v49}
+  ,~{v50},~{v51},~{v52},~{v53},~{v54},~{v55},~{v56},~{v57},~{v58},~{v59}
+  ,~{v60},~{v61},~{v62},~{v63},~{v64},~{v65},~{v66},~{v67},~{v68},~{v69}
+  ,~{v70},~{v71},~{v72},~{v73},~{v74},~{v75},~{v76},~{v77},~{v78},~{v79}
+  ,~{v80},~{v81},~{v82},~{v83},~{v84},~{v85},~{v86},~{v87},~{v88},~{v89}
+  ,~{v90},~{v91},~{v92},~{v93},~{v94},~{v95},~{v96},~{v97},~{v98},~{v99}
+  ,~{v100},~{v101},~{v102},~{v103},~{v104},~{v105},~{v106},~{v107},~{v108},~{v109}
+  ,~{v110},~{v111},~{v112},~{v113},~{v114},~{v115},~{v116},~{v117},~{v118},~{v119}
+  ,~{v120},~{v121},~{v122},~{v123},~{v124},~{v125},~{v126},~{v127},~{v128},~{v129}
+  ,~{v130},~{v131},~{v132},~{v133},~{v134},~{v135},~{v136},~{v137},~{v138},~{v139}
+  ,~{v140},~{v141},~{v142},~{v143},~{v144},~{v145},~{v146},~{v147},~{v148},~{v149}
+  ,~{v150},~{v151},~{v152},~{v153},~{v154},~{v155},~{v156},~{v157},~{v158},~{v159}
+  ,~{v160},~{v161},~{v162},~{v163},~{v164},~{v165},~{v166},~{v167},~{v168},~{v169}
+  ,~{v170},~{v171},~{v172},~{v173},~{v174},~{v175},~{v176},~{v177},~{v178},~{v179}
+  ,~{v180},~{v181},~{v182},~{v183},~{v184},~{v185},~{v186},~{v187},~{v188},~{v189}
+  ,~{v190},~{v191},~{v192},~{v193},~{v194},~{v195},~{v196},~{v197},~{v198},~{v199}
+  ,~{v200},~{v201},~{v202},~{v203},~{v204},~{v205},~{v206},~{v207},~{v208},~{v209}
+  ,~{v210},~{v211},~{v212},~{v213},~{v214},~{v215},~{v216},~{v217},~{v218},~{v219}
+  ,~{v220},~{v221},~{v222},~{v223},~{v224},~{v225},~{v226},~{v227},~{v228},~{v229}
+  ,~{v230},~{v231},~{v232},~{v233},~{v234},~{v235},~{v236},~{v237},~{v238},~{v239}
+  ,~{v240},~{v241},~{v242},~{v243},~{v244},~{v245},~{v246},~{v247},~{v248},~{v249}
+  ,~{v250},~{v251},~{v252},~{v253},~{v254}" () #0
+  musttail call void @child_function()
+  ret void
+}
+
 attributes #0 = { nounwind noinline norecurse "amdgpu-flat-work-group-size"="1,256" }