[llvm] [AMDGPU] - Add constant folding for s_bitreplicate (PR #72366)

[Jessica Del via llvm-commits]

https://github.com/OutOfCache updated https://github.com/llvm/llvm-project/pull/72366

>From 44b4463d42b206f69114859fb04a5caeadcd3312 Mon Sep 17 00:00:00 2001
From: Jessica Del <Jessica.Del at amd.com>
Date: Tue, 14 Nov 2023 21:44:56 +0100
Subject: [PATCH 1/2] [AMDGPU] - Add constant folding for s_bitreplicate

If the input is a constant, we can constant fold the s_bitreplicate
operation.
---
 llvm/lib/Analysis/ConstantFolding.cpp          | 18 ++++++++++++++++++
 .../CodeGen/AMDGPU/llvm.amdgcn.bitreplicate.ll |  4 ++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 966a65ac26b8017..e401efa6c67c2da 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1533,6 +1533,7 @@ bool llvm::canConstantFoldCallTo(const CallBase *Call, const Function *F) {
   case Intrinsic::amdgcn_perm:
   case Intrinsic::amdgcn_wave_reduce_umin:
   case Intrinsic::amdgcn_wave_reduce_umax:
+  case Intrinsic::amdgcn_s_bitreplicate:
   case Intrinsic::arm_mve_vctp8:
   case Intrinsic::arm_mve_vctp16:
   case Intrinsic::arm_mve_vctp32:
@@ -2422,6 +2423,23 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
 
       return ConstantFP::get(Ty->getContext(), Val);
     }
+
+    case Intrinsic::amdgcn_s_bitreplicate: {
+      uint64_t Val = Op->getZExtValue();
+      uint64_t ReplicatedVal = 0;
+      uint64_t ReplicatedOnes = 0b11;
+      // Input operand is always b32
+      for (unsigned i = 0; i < 32; ++i, ReplicatedOnes <<= 2, Val >>= 1) {
+        uint64_t Bit = Val & 1;
+
+        if (!Bit)
+          continue;
+
+        ReplicatedVal |= ReplicatedOnes;
+      }
+      return ConstantInt::get(Ty, ReplicatedVal);
+    }
+
     default:
       return nullptr;
     }
diff --git a/llvm/test/CodeGen/AMDGPU/llvm.amdgcn.bitreplicate.ll b/llvm/test/CodeGen/AMDGPU/llvm.amdgcn.bitreplicate.ll
index 027c9ef5e7cc349..0937280e6352c80 100644
--- a/llvm/test/CodeGen/AMDGPU/llvm.amdgcn.bitreplicate.ll
+++ b/llvm/test/CodeGen/AMDGPU/llvm.amdgcn.bitreplicate.ll
@@ -8,8 +8,8 @@ define i64 @test_s_bitreplicate_constant() {
 ; GFX11-LABEL: test_s_bitreplicate_constant:
 ; GFX11:       ; %bb.0: ; %entry
 ; GFX11-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GFX11-NEXT:    s_bitreplicate_b64_b32 s[0:1], 0x85fe3a92
-; GFX11-NEXT:    v_dual_mov_b32 v0, s0 :: v_dual_mov_b32 v1, s1
+; GFX11-NEXT:    v_mov_b32_e32 v0, 0xfccc30c
+; GFX11-NEXT:    v_mov_b32_e32 v1, 0xc033fffc
 ; GFX11-NEXT:    s_setpc_b64 s[30:31]
 entry:
   %br = call i64 @llvm.amdgcn.s.bitreplicate(i32 u0x85FE3A92)

>From 22a11897a9e28de46ac7f25acde940bb1759b4c4 Mon Sep 17 00:00:00 2001
From: Jessica Del <Jessica.Del at amd.com>
Date: Wed, 15 Nov 2023 11:25:11 +0100
Subject: [PATCH 2/2] fixup! [AMDGPU] - Add constant folding for s_bitreplicate

---
 llvm/lib/Analysis/ConstantFolding.cpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index e401efa6c67c2da..7521e45fe27bd30 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -2430,9 +2430,7 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
       uint64_t ReplicatedOnes = 0b11;
       // Input operand is always b32
       for (unsigned i = 0; i < 32; ++i, ReplicatedOnes <<= 2, Val >>= 1) {
-        uint64_t Bit = Val & 1;
-
-        if (!Bit)
+        if (!(Val & 1))
           continue;
 
         ReplicatedVal |= ReplicatedOnes;