[llvm] [AMDGPU][CodeGen] Update support (soffset + offset) s_buffer_load's (PR #68302)

via llvm-commits llvm-commits at lists.llvm.org
Thu Oct 5 07:36:51 PDT 2023 

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

<details>
<summary>Changes</summary>

getBaseWithConstantOffset() is used for scalar and non-scalar buffer loads. Diffrence between s_load and load instruction is that s_load instruction extends 32-bit offset to 64-bits, so a 32-bit (address + offset) should not cause unsigned 32-bit integer wraparound, because it performs addition in 64-bits.

---
Full diff: https://github.com/llvm/llvm-project/pull/68302.diff


4 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.cpp (+6-1) 
- (modified) llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.h (+2-1) 
- (modified) llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp (+2-2) 
- (modified) llvm/test/CodeGen/AMDGPU/amdgcn-load-offset-from-reg.ll (+70) 


``````````diff
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.cpp b/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.cpp
index 09930dc9612cca2..057b263a4e4633a 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.cpp
@@ -18,7 +18,7 @@ using namespace MIPatternMatch;
 
 std::pair<Register, unsigned>
 AMDGPU::getBaseWithConstantOffset(MachineRegisterInfo &MRI, Register Reg,
-                                  GISelKnownBits *KnownBits) {
+                                  GISelKnownBits *KnownBits, bool checkNUW) {
   MachineInstr *Def = getDefIgnoringCopies(Reg, MRI);
   if (Def->getOpcode() == TargetOpcode::G_CONSTANT) {
     unsigned Offset;
@@ -33,6 +33,11 @@ AMDGPU::getBaseWithConstantOffset(MachineRegisterInfo &MRI, Register Reg,
 
   int64_t Offset;
   if (Def->getOpcode() == TargetOpcode::G_ADD) {
+    // A 32-bit (address + offset) should not cause unsigned 32-bit integer
+    // wraparound, because s_load instructions perform the addition in 64 bits.
+    if (!Def->getFlag(MachineInstr::NoUWrap) &&
+        MRI.getType(Reg).getScalarSizeInBits() == 32 && checkNUW)
+      return std::pair(Reg, 0);
     // TODO: Handle G_OR used for add case
     if (mi_match(Def->getOperand(2).getReg(), MRI, m_ICst(Offset)))
       return std::pair(Def->getOperand(1).getReg(), Offset);
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.h b/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.h
index ff4edf02a84d78d..e921c29c6ba432d 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUGlobalISelUtils.h
@@ -25,7 +25,8 @@ namespace AMDGPU {
 /// Returns base register and constant offset.
 std::pair<Register, unsigned>
 getBaseWithConstantOffset(MachineRegisterInfo &MRI, Register Reg,
-                          GISelKnownBits *KnownBits = nullptr);
+                          GISelKnownBits *KnownBits = nullptr,
+                          bool checkNUW = false);
 
 bool hasAtomicFaddRtnForTy(const GCNSubtarget &Subtarget, const LLT &Ty);
 }
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
index 31d72fb8cadd8a6..058413366232ba4 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
@@ -4997,8 +4997,8 @@ AMDGPUInstructionSelector::selectSMRDBufferSgprImm(MachineOperand &Root) const {
   // an immediate offset.
   Register SOffset;
   unsigned Offset;
-  std::tie(SOffset, Offset) =
-      AMDGPU::getBaseWithConstantOffset(*MRI, Root.getReg(), KB);
+  std::tie(SOffset, Offset) = AMDGPU::getBaseWithConstantOffset(
+      *MRI, Root.getReg(), KB, /*checkNUW*/ true);
   if (!SOffset)
     return std::nullopt;
 
diff --git a/llvm/test/CodeGen/AMDGPU/amdgcn-load-offset-from-reg.ll b/llvm/test/CodeGen/AMDGPU/amdgcn-load-offset-from-reg.ll
index 181b5b71bdd485b..6112dac25be7fd2 100644
--- a/llvm/test/CodeGen/AMDGPU/amdgcn-load-offset-from-reg.ll
+++ b/llvm/test/CodeGen/AMDGPU/amdgcn-load-offset-from-reg.ll
@@ -109,6 +109,76 @@ define amdgpu_cs void @test_buffer_load_sgpr_plus_imm_offset(<4 x i32> inreg %ba
   ret void
 }
 
+; GCN-LABEL: name: test_buffer_load_sgpr_plus_imm_offset_nuw
+; SDAG-DAG: %[[BASE0:.*]]:sgpr_32 = COPY $sgpr0
+; SDAG-DAG: %[[BASE1:.*]]:sgpr_32 = COPY $sgpr1
+; SDAG-DAG: %[[BASE2:.*]]:sgpr_32 = COPY $sgpr2
+; SDAG-DAG: %[[BASE3:.*]]:sgpr_32 = COPY $sgpr3
+; SDAG-DAG: %[[OFFSET:.*]]:sgpr_32 = COPY $sgpr4
+; SDAG-DAG: %[[BASE:.*]]:sgpr_128 = REG_SEQUENCE %[[BASE0]], %subreg.sub0, %[[BASE1]], %subreg.sub1, %[[BASE2]], %subreg.sub2, %[[BASE3]], %subreg.sub3
+; SDAG: S_BUFFER_LOAD_DWORD_SGPR_IMM killed %[[BASE]], %[[OFFSET]], 77,
+; GISEL-DAG: %[[BASE0:.*]]:sreg_32 = COPY $sgpr0
+; GISEL-DAG: %[[BASE1:.*]]:sreg_32 = COPY $sgpr1
+; GISEL-DAG: %[[BASE2:.*]]:sreg_32 = COPY $sgpr2
+; GISEL-DAG: %[[BASE3:.*]]:sreg_32 = COPY $sgpr3
+; GISEL-DAG: %[[OFFSET:.*]]:sreg_32 = COPY $sgpr4
+; GISEL-DAG: %[[BASE:.*]]:sgpr_128 = REG_SEQUENCE %[[BASE0]], %subreg.sub0, %[[BASE1]], %subreg.sub1, %[[BASE2]], %subreg.sub2, %[[BASE3]], %subreg.sub3
+; GISEL: S_BUFFER_LOAD_DWORD_SGPR_IMM %[[BASE]], %[[OFFSET]], 77,
+define amdgpu_cs void @test_buffer_load_sgpr_plus_imm_offset_nuw(<4 x i32> inreg %base, i32 inreg %i, ptr addrspace(1) inreg %out) #0 {
+  %off = add nuw i32 %i, 77
+  %v = call i32 @llvm.amdgcn.s.buffer.load.i32(<4 x i32> %base, i32 %off, i32 0)
+  store i32 %v, ptr addrspace(1) %out, align 4
+  ret void
+}
+
+; GCN-LABEL: name: test_buffer_load_sgpr_plus_imm_offset_nsw
+; SDAG-DAG: %[[BASE0:.*]]:sgpr_32 = COPY $sgpr0
+; SDAG-DAG: %[[BASE1:.*]]:sgpr_32 = COPY $sgpr1
+; SDAG-DAG: %[[BASE2:.*]]:sgpr_32 = COPY $sgpr2
+; SDAG-DAG: %[[BASE3:.*]]:sgpr_32 = COPY $sgpr3
+; SDAG-DAG: %[[OFFSET:.*]]:sgpr_32 = COPY $sgpr4
+; SDAG-DAG: %[[BASE:.*]]:sgpr_128 = REG_SEQUENCE %[[BASE0]], %subreg.sub0, %[[BASE1]], %subreg.sub1, %[[BASE2]], %subreg.sub2, %[[BASE3]], %subreg.sub3
+; SDAG-DAG: %[[ADD:.*]]:sreg_32 = nsw S_ADD_I32 %4, killed %11, implicit-def dead $scc
+; SDAG: S_BUFFER_LOAD_DWORD_SGPR_IMM killed %[[BASE]], killed %[[ADD]], 0,
+; GISEL-DAG: %[[BASE0:.*]]:sreg_32 = COPY $sgpr0
+; GISEL-DAG: %[[BASE1:.*]]:sreg_32 = COPY $sgpr1
+; GISEL-DAG: %[[BASE2:.*]]:sreg_32 = COPY $sgpr2
+; GISEL-DAG: %[[BASE3:.*]]:sreg_32 = COPY $sgpr3
+; GISEL-DAG: %[[OFFSET:.*]]:sreg_32 = COPY $sgpr4
+; GISEL-DAG: %[[BASE:.*]]:sgpr_128 = REG_SEQUENCE %[[BASE0]], %subreg.sub0, %[[BASE1]], %subreg.sub1, %[[BASE2]], %subreg.sub2, %[[BASE3]], %subreg.sub3
+; GISEL-DAG: %[[ADD:.*]]:sreg_32 = nsw S_ADD_I32 %1, %10, implicit-def dead $scc
+; GISEL: S_BUFFER_LOAD_DWORD_SGPR_IMM %[[BASE]], %[[ADD]], 0,
+define amdgpu_cs void @test_buffer_load_sgpr_plus_imm_offset_nsw(<4 x i32> inreg %base, i32 inreg %i, ptr addrspace(1) inreg %out) #0 {
+    %off = add nsw i32 %i, 77
+    %v = call i32 @llvm.amdgcn.s.buffer.load.i32(<4 x i32> %base, i32 %off, i32 0)
+    store i32 %v, ptr addrspace(1) %out, align 4
+    ret void
+  }
+
+; GCN-LABEL: name: test_buffer_load_sgpr_plus_imm_offset_noflags
+; SDAG-DAG: %[[BASE0:.*]]:sgpr_32 = COPY $sgpr0
+; SDAG-DAG: %[[BASE1:.*]]:sgpr_32 = COPY $sgpr1
+; SDAG-DAG: %[[BASE2:.*]]:sgpr_32 = COPY $sgpr2
+; SDAG-DAG: %[[BASE3:.*]]:sgpr_32 = COPY $sgpr3
+; SDAG-DAG: %[[OFFSET:.*]]:sgpr_32 = COPY $sgpr4
+; SDAG-DAG: %[[BASE:.*]]:sgpr_128 = REG_SEQUENCE %[[BASE0]], %subreg.sub0, %[[BASE1]], %subreg.sub1, %[[BASE2]], %subreg.sub2, %[[BASE3]], %subreg.sub3
+; SDAG-DAG: %[[ADD:.*]]:sreg_32 = S_ADD_I32 %4, killed %11, implicit-def dead $scc
+; SDAG: S_BUFFER_LOAD_DWORD_SGPR_IMM killed %[[BASE]], killed %[[ADD]], 0,
+; GISEL-DAG: %[[BASE0:.*]]:sreg_32 = COPY $sgpr0
+; GISEL-DAG: %[[BASE1:.*]]:sreg_32 = COPY $sgpr1
+; GISEL-DAG: %[[BASE2:.*]]:sreg_32 = COPY $sgpr2
+; GISEL-DAG: %[[BASE3:.*]]:sreg_32 = COPY $sgpr3
+; GISEL-DAG: %[[OFFSET:.*]]:sreg_32 = COPY $sgpr4
+; GISEL-DAG: %[[BASE:.*]]:sgpr_128 = REG_SEQUENCE %[[BASE0]], %subreg.sub0, %[[BASE1]], %subreg.sub1, %[[BASE2]], %subreg.sub2, %[[BASE3]], %subreg.sub3
+; GISEL-DAG: %[[ADD:.*]]:sreg_32 = S_ADD_I32 %1, %10, implicit-def dead $scc
+; GISEL: S_BUFFER_LOAD_DWORD_SGPR_IMM %[[BASE]], %[[ADD]], 0,
+define amdgpu_cs void @test_buffer_load_sgpr_plus_imm_offset_noflags(<4 x i32> inreg %base, i32 inreg %i, ptr addrspace(1) inreg %out) #0 {
+    %off = add i32 %i, 77
+    %v = call i32 @llvm.amdgcn.s.buffer.load.i32(<4 x i32> %base, i32 %off, i32 0)
+    store i32 %v, ptr addrspace(1) %out, align 4
+    ret void
+  }
+
 ; GCN-LABEL: name: test_buffer_load_sgpr_or_imm_offset
 ; SDAG-DAG: %[[BASE0:.*]]:sgpr_32 = COPY $sgpr0
 ; SDAG-DAG: %[[BASE1:.*]]:sgpr_32 = COPY $sgpr1

``````````

</details>


https://github.com/llvm/llvm-project/pull/68302

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